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  1. 28 5月, 2022 2 次提交
  3. 10 5月, 2022 2 次提交
  5. 29 4月, 2022 1 次提交
  7. 02 4月, 2022 1 次提交
  9. 25 3月, 2022 2 次提交
    • J
      mm: madvise: MADV_DONTNEED_LOCKED · 9457056a
      由 Johannes Weiner 提交于 
      MADV_DONTNEED historically rejects mlocked ranges, but with MLOCK_ONFAULT
and MCL_ONFAULT allowing to mlock without populating, there are valid use
cases for depopulating locked ranges as well.

Users mlock memory to protect secrets.  There are allocators for secure
buffers that want in-use memory generally mlocked, but cleared and
invalidated memory to give up the physical pages.  This could be done with
explicit munlock -> mlock calls on free -> alloc of course, but that adds
two unnecessary syscalls, heavy mmap_sem write locks, vma splits and
re-merges - only to get rid of the backing pages.

Users also mlockall(MCL_ONFAULT) to suppress sustained paging, but are
okay with on-demand initial population.  It seems valid to selectively
free some memory during the lifetime of such a process, without having to
mess with its overall policy.

Why add a separate flag? Isn't this a pretty niche usecase?

- MADV_DONTNEED has been bailing on locked vmas forever. It's at least
  conceivable that someone, somewhere is relying on mlock to protect
  data from perhaps broader invalidation calls. Changing this behavior
  now could lead to quiet data corruption.

- It also clarifies expectations around MADV_FREE and maybe
  MADV_REMOVE. It avoids the situation where one quietly behaves
  different than the others. MADV_FREE_LOCKED can be added later.

- The combination of mlock() and madvise() in the first place is
  probably niche. But where it happens, I'd say that dropping pages
  from a locked region once they don't contain secrets or won't page
  anymore is much saner than relying on mlock to protect memory from
  speculative or errant invalidation calls. It's just that we can't
  change the default behavior because of the two previous points.

Given that, an explicit new flag seems to make the most sense.

[hannes@cmpxchg.org: fix mips build]

Link: https://lkml.kernel.org/r/20220304171912.305060-1-hannes@cmpxchg.orgSigned-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.com>
Reviewed-by: NMike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: NShakeel Butt <shakeelb@google.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      9457056a
    • M
      mm: enable MADV_DONTNEED for hugetlb mappings · 90e7e7f5
      由 Mike Kravetz 提交于 
      Patch series "Add hugetlb MADV_DONTNEED support", v3.

Userfaultfd selftests for hugetlb does not perform UFFD_EVENT_REMAP
testing.  However, mremap support was recently added in commit
550a7d60 ("mm, hugepages: add mremap() support for hugepage backed
vma").  While attempting to enable mremap support in the test, it was
discovered that the mremap test indirectly depends on MADV_DONTNEED.

madvise does not allow MADV_DONTNEED for hugetlb mappings.  However, that
is primarily due to the check in can_madv_lru_vma().  By simply removing
the check and adding huge page alignment, MADV_DONTNEED can be made to
work for hugetlb mappings.

Do note that there is no compelling use case for adding this support.
This was discussed in the RFC [1].  However, adding support makes sense as
it is fairly trivial and brings hugetlb functionality more in line with
'normal' memory.

After enabling support, add selftest for MADV_DONTNEED as well as
MADV_REMOVE.  Then update userfaultfd selftest.

If new functionality is accepted, then madvise man page will be updated to
indicate hugetlb is supported.  It will also be updated to clarify what
happens to the passed length argument.

This patch (of 3):

MADV_DONTNEED is currently disabled for hugetlb mappings.  This certainly
makes sense in shared file mappings as the pagecache maintains a reference
to the page and it will never be freed.  However, it could be useful to
unmap and free pages in private mappings.  In addition, userfaultfd minor
fault users may be able to simplify code by using MADV_DONTNEED.

The primary thing preventing MADV_DONTNEED from working on hugetlb
mappings is a check in can_madv_lru_vma().  To allow support for hugetlb
mappings create and use a new routine madvise_dontneed_free_valid_vma()
that allows hugetlb mappings in this specific case.

For normal mappings, madvise requires the start address be PAGE aligned
and rounds up length to the next multiple of PAGE_SIZE.  Do similarly for
hugetlb mappings: require start address be huge page size aligned and
round up length to the next multiple of huge page size.  Use the new
madvise_dontneed_free_valid_vma routine to check alignment and round up
length/end.  zap_page_range requires this alignment for hugetlb vmas
otherwise we will hit BUGs.

Link: https://lkml.kernel.org/r/20220215002348.128823-1-mike.kravetz@oracle.com
Link: https://lkml.kernel.org/r/20220215002348.128823-2-mike.kravetz@oracle.comSigned-off-by: NMike Kravetz <mike.kravetz@oracle.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: David Hildenbrand <david@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      90e7e7f5
  11. 23 3月, 2022 4 次提交
  13. 06 3月, 2022 3 次提交
    • S
      mm: fix use-after-free when anon vma name is used after vma is freed · 942341dc
      由 Suren Baghdasaryan 提交于 
      When adjacent vmas are being merged it can result in the vma that was
originally passed to madvise_update_vma being destroyed.  In the current
implementation, the name parameter passed to madvise_update_vma points
directly to vma->anon_name and it is used after the call to vma_merge.
In the cases when vma_merge merges the original vma and destroys it,
this might result in UAF.  For that the original vma would have to hold
the anon_vma_name with the last reference.  The following vma would need
to contain a different anon_vma_name object with the same string.  Such
scenario is shown below:

madvise_vma_behavior(vma)
  madvise_update_vma(vma, ..., anon_name == vma->anon_name)
    vma_merge(vma)
      __vma_adjust(vma) <-- merges vma with adjacent one
        vm_area_free(vma) <-- frees the original vma
    replace_vma_anon_name(anon_name) <-- UAF of vma->anon_name

Fix this by raising the name refcount and stabilizing it.

Link: https://lkml.kernel.org/r/20220224231834.1481408-3-surenb@google.com
Link: https://lkml.kernel.org/r/20220223153613.835563-3-surenb@google.com
Fixes: 9a10064f ("mm: add a field to store names for private anonymous memory")
Signed-off-by: NSuren Baghdasaryan <surenb@google.com>
Reported-by: syzbot+aa7b3d4b35f9dc46a366@syzkaller.appspotmail.com
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Alexey Gladkov <legion@kernel.org>
Cc: Chris Hyser <chris.hyser@oracle.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Colin Cross <ccross@google.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xiaofeng Cao <caoxiaofeng@yulong.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      942341dc
    • S
      mm: prevent vm_area_struct::anon_name refcount saturation · 96403e11
      由 Suren Baghdasaryan 提交于 
      A deep process chain with many vmas could grow really high.  With
default sysctl_max_map_count (64k) and default pid_max (32k) the max
number of vmas in the system is 2147450880 and the refcounter has
headroom of 1073774592 before it reaches REFCOUNT_SATURATED
(3221225472).

Therefore it's unlikely that an anonymous name refcounter will overflow
with these defaults.  Currently the max for pid_max is PID_MAX_LIMIT
(4194304) and for sysctl_max_map_count it's INT_MAX (2147483647).  In
this configuration anon_vma_name refcount overflow becomes theoretically
possible (that still require heavy sharing of that anon_vma_name between
processes).

kref refcounting interface used in anon_vma_name structure will detect a
counter overflow when it reaches REFCOUNT_SATURATED value but will only
generate a warning and freeze the ref counter.  This would lead to the
refcounted object never being freed.  A determined attacker could leak
memory like that but it would be rather expensive and inefficient way to
do so.

To ensure anon_vma_name refcount does not overflow, stop anon_vma_name
sharing when the refcount reaches REFCOUNT_MAX (2147483647), which still
leaves INT_MAX/2 (1073741823) values before the counter reaches
REFCOUNT_SATURATED.  This should provide enough headroom for raising the
refcounts temporarily.

Link: https://lkml.kernel.org/r/20220223153613.835563-2-surenb@google.comSigned-off-by: NSuren Baghdasaryan <surenb@google.com>
Suggested-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Alexey Gladkov <legion@kernel.org>
Cc: Chris Hyser <chris.hyser@oracle.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Colin Cross <ccross@google.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xiaofeng Cao <caoxiaofeng@yulong.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      96403e11
    • S
      mm: refactor vm_area_struct::anon_vma_name usage code · 5c26f6ac
      由 Suren Baghdasaryan 提交于 
      Avoid mixing strings and their anon_vma_name referenced pointers by
using struct anon_vma_name whenever possible.  This simplifies the code
and allows easier sharing of anon_vma_name structures when they
represent the same name.

[surenb@google.com: fix comment]

Link: https://lkml.kernel.org/r/20220223153613.835563-1-surenb@google.com
Link: https://lkml.kernel.org/r/20220224231834.1481408-1-surenb@google.comSigned-off-by: NSuren Baghdasaryan <surenb@google.com>
Suggested-by: NMatthew Wilcox <willy@infradead.org>
Suggested-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Colin Cross <ccross@google.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Alexey Gladkov <legion@kernel.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Chris Hyser <chris.hyser@oracle.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Xiaofeng Cao <caoxiaofeng@yulong.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      5c26f6ac
  15. 18 2月, 2022 1 次提交
    • H
      mm/munlock: delete munlock_vma_pages_all(), allow oomreap · a213e5cf
      由 Hugh Dickins 提交于 
      munlock_vma_pages_range() will still be required, when munlocking but
not munmapping a set of pages; but when unmapping a pte, the mlock count
will be maintained in much the same way as it will be maintained when
mapping in the pte.  Which removes the need for munlock_vma_pages_all()
on mlocked vmas when munmapping or exiting: eliminating the catastrophic
contention on i_mmap_rwsem, and the need for page lock on the pages.

There is still a need to update locked_vm accounting according to the
munmapped vmas when munmapping: do that in detach_vmas_to_be_unmapped().
exit_mmap() does not need locked_vm updates, so delete unlock_range().

And wasn't I the one who forbade the OOM reaper to attack mlocked vmas,
because of the uncertainty in blocking on all those page locks?
No fear of that now, so permit the OOM reaper on mlocked vmas.
Signed-off-by: NHugh Dickins <hughd@google.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
      a213e5cf
  17. 15 1月, 2022 4 次提交
    • A
      mm: move anon_vma declarations to linux/mm_inline.h · 17fca131
      由 Arnd Bergmann 提交于 
      The patch to add anonymous vma names causes a build failure in some
configurations:

  include/linux/mm_types.h: In function 'is_same_vma_anon_name':
  include/linux/mm_types.h:924:37: error: implicit declaration of function 'strcmp' [-Werror=implicit-function-declaration]
    924 |         return name && vma_name && !strcmp(name, vma_name);
        |                                     ^~~~~~
  include/linux/mm_types.h:22:1: note: 'strcmp' is defined in header '<string.h>'; did you forget to '#include <string.h>'?

This should not really be part of linux/mm_types.h in the first place,
as that header is meant to only contain structure defintions and need a
minimum set of indirect includes itself.

While the header clearly includes more than it should at this point,
let's not make it worse by including string.h as well, which would pull
in the expensive (compile-speed wise) fortify-string logic.

Move the new functions into a separate header that only needs to be
included in a couple of locations.

Link: https://lkml.kernel.org/r/20211207125710.2503446-1-arnd@kernel.org
Fixes: "mm: add a field to store names for private anonymous memory"
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Colin Cross <ccross@google.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      17fca131
    • S
      mm: add anonymous vma name refcounting · 78db3412
      由 Suren Baghdasaryan 提交于 
      While forking a process with high number (64K) of named anonymous vmas
the overhead caused by strdup() is noticeable.  Experiments with ARM64
Android device show up to 40% performance regression when forking a
process with 64k unpopulated anonymous vmas using the max name lengths
vs the same process with the same number of anonymous vmas having no
name.

Introduce anon_vma_name refcounted structure to avoid the overhead of
copying vma names during fork() and when splitting named anonymous vmas.

When a vma is duplicated, instead of copying the name we increment the
refcount of this structure.  Multiple vmas can point to the same
anon_vma_name as long as they increment the refcount.  The name member
of anon_vma_name structure is assigned at structure allocation time and
is never changed.  If vma name changes then the refcount of the original
structure is dropped, a new anon_vma_name structure is allocated to hold
the new name and the vma pointer is updated to point to the new
structure.

With this approach the fork() performance regressions is reduced 3-4x
times and with usecases using more reasonable number of VMAs (a few
thousand) the regressions is not measurable.

Link: https://lkml.kernel.org/r/20211019215511.3771969-3-surenb@google.comSigned-off-by: NSuren Baghdasaryan <surenb@google.com>
Reviewed-by: NKees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Colin Cross <ccross@google.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jan Glauber <jan.glauber@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rob Landley <rob@landley.net>
Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>
Cc: Shaohua Li <shli@fusionio.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      78db3412
    • C
      mm: add a field to store names for private anonymous memory · 9a10064f
      由 Colin Cross 提交于 
      In many userspace applications, and especially in VM based applications
like Android uses heavily, there are multiple different allocators in
use.  At a minimum there is libc malloc and the stack, and in many cases
there are libc malloc, the stack, direct syscalls to mmap anonymous
memory, and multiple VM heaps (one for small objects, one for big
objects, etc.).  Each of these layers usually has its own tools to
inspect its usage; malloc by compiling a debug version, the VM through
heap inspection tools, and for direct syscalls there is usually no way
to track them.

On Android we heavily use a set of tools that use an extended version of
the logic covered in Documentation/vm/pagemap.txt to walk all pages
mapped in userspace and slice their usage by process, shared (COW) vs.
unique mappings, backing, etc.  This can account for real physical
memory usage even in cases like fork without exec (which Android uses
heavily to share as many private COW pages as possible between
processes), Kernel SamePage Merging, and clean zero pages.  It produces
a measurement of the pages that only exist in that process (USS, for
unique), and a measurement of the physical memory usage of that process
with the cost of shared pages being evenly split between processes that
share them (PSS).

If all anonymous memory is indistinguishable then figuring out the real
physical memory usage (PSS) of each heap requires either a pagemap
walking tool that can understand the heap debugging of every layer, or
for every layer's heap debugging tools to implement the pagemap walking
logic, in which case it is hard to get a consistent view of memory
across the whole system.

Tracking the information in userspace leads to all sorts of problems.
It either needs to be stored inside the process, which means every
process has to have an API to export its current heap information upon
request, or it has to be stored externally in a filesystem that somebody
needs to clean up on crashes.  It needs to be readable while the process
is still running, so it has to have some sort of synchronization with
every layer of userspace.  Efficiently tracking the ranges requires
reimplementing something like the kernel vma trees, and linking to it
from every layer of userspace.  It requires more memory, more syscalls,
more runtime cost, and more complexity to separately track regions that
the kernel is already tracking.

This patch adds a field to /proc/pid/maps and /proc/pid/smaps to show a
userspace-provided name for anonymous vmas.  The names of named
anonymous vmas are shown in /proc/pid/maps and /proc/pid/smaps as
[anon:<name>].

Userspace can set the name for a region of memory by calling

   prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name)

Setting the name to NULL clears it.  The name length limit is 80 bytes
including NUL-terminator and is checked to contain only printable ascii
characters (including space), except '[',']','\','$' and '`'.

Ascii strings are being used to have a descriptive identifiers for vmas,
which can be understood by the users reading /proc/pid/maps or
/proc/pid/smaps.  Names can be standardized for a given system and they
can include some variable parts such as the name of the allocator or a
library, tid of the thread using it, etc.

The name is stored in a pointer in the shared union in vm_area_struct
that points to a null terminated string.  Anonymous vmas with the same
name (equivalent strings) and are otherwise mergeable will be merged.
The name pointers are not shared between vmas even if they contain the
same name.  The name pointer is stored in a union with fields that are
only used on file-backed mappings, so it does not increase memory usage.

CONFIG_ANON_VMA_NAME kernel configuration is introduced to enable this
feature.  It keeps the feature disabled by default to prevent any
additional memory overhead and to avoid confusing procfs parsers on
systems which are not ready to support named anonymous vmas.

The patch is based on the original patch developed by Colin Cross, more
specifically on its latest version [1] posted upstream by Sumit Semwal.
It used a userspace pointer to store vma names.  In that design, name
pointers could be shared between vmas.  However during the last
upstreaming attempt, Kees Cook raised concerns [2] about this approach
and suggested to copy the name into kernel memory space, perform
validity checks [3] and store as a string referenced from
vm_area_struct.

One big concern is about fork() performance which would need to strdup
anonymous vma names.  Dave Hansen suggested experimenting with
worst-case scenario of forking a process with 64k vmas having longest
possible names [4].  I ran this experiment on an ARM64 Android device
and recorded a worst-case regression of almost 40% when forking such a
process.

This regression is addressed in the followup patch which replaces the
pointer to a name with a refcounted structure that allows sharing the
name pointer between vmas of the same name.  Instead of duplicating the
string during fork() or when splitting a vma it increments the refcount.

[1] https://lore.kernel.org/linux-mm/20200901161459.11772-4-sumit.semwal@linaro.org/
[2] https://lore.kernel.org/linux-mm/202009031031.D32EF57ED@keescook/
[3] https://lore.kernel.org/linux-mm/202009031022.3834F692@keescook/
[4] https://lore.kernel.org/linux-mm/5d0358ab-8c47-2f5f-8e43-23b89d6a8e95@intel.com/

Changes for prctl(2) manual page (in the options section):

PR_SET_VMA
	Sets an attribute specified in arg2 for virtual memory areas
	starting from the address specified in arg3 and spanning the
	size specified	in arg4. arg5 specifies the value of the attribute
	to be set. Note that assigning an attribute to a virtual memory
	area might prevent it from being merged with adjacent virtual
	memory areas due to the difference in that attribute's value.

	Currently, arg2 must be one of:

	PR_SET_VMA_ANON_NAME
		Set a name for anonymous virtual memory areas. arg5 should
		be a pointer to a null-terminated string containing the
		name. The name length including null byte cannot exceed
		80 bytes. If arg5 is NULL, the name of the appropriate
		anonymous virtual memory areas will be reset. The name
		can contain only printable ascii characters (including
                space), except '[',']','\','$' and '`'.

                This feature is available only if the kernel is built with
                the CONFIG_ANON_VMA_NAME option enabled.

[surenb@google.com: docs: proc.rst: /proc/PID/maps: fix malformed table]
  Link: https://lkml.kernel.org/r/20211123185928.2513763-1-surenb@google.com
[surenb: rebased over v5.15-rc6, replaced userpointer with a kernel copy,
 added input sanitization and CONFIG_ANON_VMA_NAME config. The bulk of the
 work here was done by Colin Cross, therefore, with his permission, keeping
 him as the author]

Link: https://lkml.kernel.org/r/20211019215511.3771969-2-surenb@google.comSigned-off-by: NColin Cross <ccross@google.com>
Signed-off-by: NSuren Baghdasaryan <surenb@google.com>
Reviewed-by: NKees Cook <keescook@chromium.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jan Glauber <jan.glauber@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rob Landley <rob@landley.net>
Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>
Cc: Shaohua Li <shli@fusionio.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      9a10064f
    • C
      mm: rearrange madvise code to allow for reuse · ac1e9acc
      由 Colin Cross 提交于 
      Patch series "mm: rearrange madvise code to allow for reuse", v11.

Avoid performance regression of the new anon vma name field refcounting it.

I checked the image sizes with allnoconfig builds:

  unpatched Linus' ToT
     text    data     bss     dec     hex filename
  1324759      32   73928 1398719 1557bf vmlinux

  After the first patch is applied (madvise refactoring)
     text    data     bss     dec     hex filename
  1322346      32   73928 1396306 154e52 vmlinux
  >>> 2413 bytes decrease vs ToT <<<

  After all patches applied with CONFIG_ANON_VMA_NAME=n
     text    data     bss     dec     hex filename
  1322337      32   73928 1396297 154e49 vmlinux
  >>> 2422 bytes decrease vs ToT <<<

  After all patches applied with CONFIG_ANON_VMA_NAME=y
     text    data     bss     dec     hex filename
  1325228      32   73928 1399188 155994 vmlinux
  >>> 469 bytes increase vs ToT <<<

This patch (of 3):

Refactor the madvise syscall to allow for parts of it to be reused by a
prctl syscall that affects vmas.

Move the code that walks vmas in a virtual address range into a function
that takes a function pointer as a parameter.  The only caller for now
is sys_madvise, which uses it to call madvise_vma_behavior on each vma,
but the next patch will add an additional caller.

Move handling all vma behaviors inside madvise_behavior, and rename it
to madvise_vma_behavior.

Move the code that updates the flags on a vma, including splitting or
merging the vma as necessary, into a new function called
madvise_update_vma.  The next patch will add support for updating a new
anon_name field as well.

Link: https://lkml.kernel.org/r/20211019215511.3771969-1-surenb@google.comSigned-off-by: NColin Cross <ccross@google.com>
Signed-off-by: NSuren Baghdasaryan <surenb@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Jan Glauber <jan.glauber@gmail.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Rob Landley <rob@landley.net>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Shaohua Li <shli@fusionio.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      ac1e9acc
  19. 14 10月, 2021 1 次提交
  21. 04 9月, 2021 1 次提交
  23. 14 8月, 2021 1 次提交
    • D
      mm/madvise: report SIGBUS as -EFAULT for MADV_POPULATE_(READ|WRITE) · eb2faa51
      由 David Hildenbrand 提交于 
      Doing some extended tests and polishing the man page update for
MADV_POPULATE_(READ|WRITE), I realized that we end up converting also
SIGBUS (via -EFAULT) to -EINVAL, making it look like yet another
madvise() user error.

We want to report only problematic mappings and permission problems that
the user could have know as -EINVAL.

Let's not convert -EFAULT arising due to SIGBUS (or SIGSEGV) to -EINVAL,
but instead indicate -EFAULT to user space.  While we could also convert
it to -ENOMEM, using -EFAULT looks more helpful when user space might
want to troubleshoot what's going wrong: MADV_POPULATE_(READ|WRITE) is
not part of an final Linux release and we can still adjust the behavior.

Link: https://lkml.kernel.org/r/20210726154932.102880-1-david@redhat.com
Fixes: 4ca9b385 ("mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables")
Signed-off-by: NDavid Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rolf Eike Beer <eike-kernel@sf-tec.de>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      eb2faa51
  25. 13 7月, 2021 1 次提交
  27. 01 7月, 2021 1 次提交
    • D
      mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables · 4ca9b385
      由 David Hildenbrand 提交于 
      I. Background: Sparse Memory Mappings

When we manage sparse memory mappings dynamically in user space - also
sometimes involving MAP_NORESERVE - we want to dynamically populate/
discard memory inside such a sparse memory region.  Example users are
hypervisors (especially implementing memory ballooning or similar
technologies like virtio-mem) and memory allocators.  In addition, we want
to fail in a nice way (instead of generating SIGBUS) if populating does
not succeed because we are out of backend memory (which can happen easily
with file-based mappings, especially tmpfs and hugetlbfs).

While MADV_DONTNEED, MADV_REMOVE and FALLOC_FL_PUNCH_HOLE allow for
reliably discarding memory for most mapping types, there is no generic
approach to populate page tables and preallocate memory.

Although mmap() supports MAP_POPULATE, it is not applicable to the concept
of sparse memory mappings, where we want to populate/discard dynamically
and avoid expensive/problematic remappings.  In addition, we never
actually report errors during the final populate phase - it is best-effort
only.

fallocate() can be used to preallocate file-based memory and fail in a
safe way.  However, it cannot really be used for any private mappings on
anonymous files via memfd due to COW semantics.  In addition, fallocate()
does not actually populate page tables, so we still always get pagefaults
on first access - which is sometimes undesired (i.e., real-time workloads)
and requires real prefaulting of page tables, not just a preallocation of
backend storage.  There might be interesting use cases for sparse memory
regions along with mlockall(MCL_ONFAULT) which fallocate() cannot satisfy
as it does not prefault page tables.

II. On preallcoation/prefaulting from user space

Because we don't have a proper interface, what applications (like QEMU and
databases) end up doing is touching (i.e., reading+writing one byte to not
overwrite existing data) all individual pages.

However, that approach
1) Can result in wear on storage backing, because we end up reading/writing
   each page; this is especially a problem for dax/pmem.
2) Can result in mmap_sem contention when prefaulting via multiple
   threads.
3) Requires expensive signal handling, especially to catch SIGBUS in case
   of hugetlbfs/shmem/file-backed memory. For example, this is
   problematic in hypervisors like QEMU where SIGBUS handlers might already
   be used by other subsystems concurrently to e.g, handle hardware errors.
   "Simply" doing preallocation concurrently from other thread is not that
   easy.

III. On MADV_WILLNEED

Extending MADV_WILLNEED is not an option because
1. It would change the semantics: "Expect access in the near future." and
   "might be a good idea to read some pages" vs. "Definitely populate/
   preallocate all memory and definitely fail on errors.".
2. Existing users (like virtio-balloon in QEMU when deflating the balloon)
   don't want populate/prealloc semantics. They treat this rather as a hint
   to give a little performance boost without too much overhead - and don't
   expect that a lot of memory might get consumed or a lot of time
   might be spent.

IV. MADV_POPULATE_READ and MADV_POPULATE_WRITE

Let's introduce MADV_POPULATE_READ and MADV_POPULATE_WRITE, inspired by
MAP_POPULATE, with the following semantics:
1. MADV_POPULATE_READ can be used to prefault page tables just like
   manually reading each individual page. This will not break any COW
   mappings. The shared zero page might get mapped and no backend storage
   might get preallocated -- allocation might be deferred to
   write-fault time. Especially shared file mappings require an explicit
   fallocate() upfront to actually preallocate backend memory (blocks in
   the file system) in case the file might have holes.
2. If MADV_POPULATE_READ succeeds, all page tables have been populated
   (prefaulted) readable once.
3. MADV_POPULATE_WRITE can be used to preallocate backend memory and
   prefault page tables just like manually writing (or
   reading+writing) each individual page. This will break any COW
   mappings -- e.g., the shared zeropage is never populated.
4. If MADV_POPULATE_WRITE succeeds, all page tables have been populated
   (prefaulted) writable once.
5. MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot be applied to special
   mappings marked with VM_PFNMAP and VM_IO. Also, proper access
   permissions (e.g., PROT_READ, PROT_WRITE) are required. If any such
   mapping is encountered, madvise() fails with -EINVAL.
6. If MADV_POPULATE_READ or MADV_POPULATE_WRITE fails, some page tables
   might have been populated.
7. MADV_POPULATE_READ and MADV_POPULATE_WRITE will return -EHWPOISON
   when encountering a HW poisoned page in the range.
8. Similar to MAP_POPULATE, MADV_POPULATE_READ and MADV_POPULATE_WRITE
   cannot protect from the OOM (Out Of Memory) handler killing the
   process.

While the use case for MADV_POPULATE_WRITE is fairly obvious (i.e.,
preallocate memory and prefault page tables for VMs), one issue is that
whenever we prefault pages writable, the pages have to be marked dirty,
because the CPU could dirty them any time.  while not a real problem for
hugetlbfs or dax/pmem, it can be a problem for shared file mappings: each
page will be marked dirty and has to be written back later when evicting.

MADV_POPULATE_READ allows for optimizing this scenario: Pre-read a whole
mapping from backend storage without marking it dirty, such that eviction
won't have to write it back.  As discussed above, shared file mappings
might require an explciit fallocate() upfront to achieve
preallcoation+prepopulation.

Although sparse memory mappings are the primary use case, this will also
be useful for other preallocate/prefault use cases where MAP_POPULATE is
not desired or the semantics of MAP_POPULATE are not sufficient: as one
example, QEMU users can trigger preallocation/prefaulting of guest RAM
after the mapping was created -- and don't want errors to be silently
suppressed.

Looking at the history, MADV_POPULATE was already proposed in 2013 [1],
however, the main motivation back than was performance improvements --
which should also still be the case.

V. Single-threaded performance comparison

I did a short experiment, prefaulting page tables on completely *empty
mappings/files* and repeated the experiment 10 times.  The results
correspond to the shortest execution time.  In general, the performance
benefit for huge pages is negligible with small mappings.

V.1: Private mappings

POPULATE_READ and POPULATE_WRITE is fastest.  Note that
Reading/POPULATE_READ will populate the shared zeropage where applicable
-- which result in short population times.

The fastest way to allocate backend storage (here: swap or huge pages) and
prefault page tables is POPULATE_WRITE.

V.2: Shared mappings

fallocate() is fastest, however, doesn't prefault page tables.
POPULATE_WRITE is faster than simple writes and read/writes.
POPULATE_READ is faster than simple reads.

Without a fd, the fastest way to allocate backend storage and prefault
page tables is POPULATE_WRITE.  With an fd, the fastest way is usually
FALLOCATE+POPULATE_READ or FALLOCATE+POPULATE_WRITE respectively; one
exception are actual files: FALLOCATE+Read is slightly faster than
FALLOCATE+POPULATE_READ.

The fastest way to allocate backend storage prefault page tables is
FALLOCATE+POPULATE_WRITE -- except when dealing with actual files; then,
FALLOCATE+POPULATE_READ is fastest and won't directly mark all pages as
dirty.

v.3: Detailed results

==================================================
2 MiB MAP_PRIVATE:
**************************************************
Anon 4 KiB     : Read                     :     0.119 ms
Anon 4 KiB     : Write                    :     0.222 ms
Anon 4 KiB     : Read/Write               :     0.380 ms
Anon 4 KiB     : POPULATE_READ            :     0.060 ms
Anon 4 KiB     : POPULATE_WRITE           :     0.158 ms
Memfd 4 KiB    : Read                     :     0.034 ms
Memfd 4 KiB    : Write                    :     0.310 ms
Memfd 4 KiB    : Read/Write               :     0.362 ms
Memfd 4 KiB    : POPULATE_READ            :     0.039 ms
Memfd 4 KiB    : POPULATE_WRITE           :     0.229 ms
Memfd 2 MiB    : Read                     :     0.030 ms
Memfd 2 MiB    : Write                    :     0.030 ms
Memfd 2 MiB    : Read/Write               :     0.030 ms
Memfd 2 MiB    : POPULATE_READ            :     0.030 ms
Memfd 2 MiB    : POPULATE_WRITE           :     0.030 ms
tmpfs          : Read                     :     0.033 ms
tmpfs          : Write                    :     0.313 ms
tmpfs          : Read/Write               :     0.406 ms
tmpfs          : POPULATE_READ            :     0.039 ms
tmpfs          : POPULATE_WRITE           :     0.285 ms
file           : Read                     :     0.033 ms
file           : Write                    :     0.351 ms
file           : Read/Write               :     0.408 ms
file           : POPULATE_READ            :     0.039 ms
file           : POPULATE_WRITE           :     0.290 ms
hugetlbfs      : Read                     :     0.030 ms
hugetlbfs      : Write                    :     0.030 ms
hugetlbfs      : Read/Write               :     0.030 ms
hugetlbfs      : POPULATE_READ            :     0.030 ms
hugetlbfs      : POPULATE_WRITE           :     0.030 ms
**************************************************
4096 MiB MAP_PRIVATE:
**************************************************
Anon 4 KiB     : Read                     :   237.940 ms
Anon 4 KiB     : Write                    :   708.409 ms
Anon 4 KiB     : Read/Write               :  1054.041 ms
Anon 4 KiB     : POPULATE_READ            :   124.310 ms
Anon 4 KiB     : POPULATE_WRITE           :   572.582 ms
Memfd 4 KiB    : Read                     :   136.928 ms
Memfd 4 KiB    : Write                    :   963.898 ms
Memfd 4 KiB    : Read/Write               :  1106.561 ms
Memfd 4 KiB    : POPULATE_READ            :    78.450 ms
Memfd 4 KiB    : POPULATE_WRITE           :   805.881 ms
Memfd 2 MiB    : Read                     :   357.116 ms
Memfd 2 MiB    : Write                    :   357.210 ms
Memfd 2 MiB    : Read/Write               :   357.606 ms
Memfd 2 MiB    : POPULATE_READ            :   356.094 ms
Memfd 2 MiB    : POPULATE_WRITE           :   356.937 ms
tmpfs          : Read                     :   137.536 ms
tmpfs          : Write                    :   954.362 ms
tmpfs          : Read/Write               :  1105.954 ms
tmpfs          : POPULATE_READ            :    80.289 ms
tmpfs          : POPULATE_WRITE           :   822.826 ms
file           : Read                     :   137.874 ms
file           : Write                    :   987.025 ms
file           : Read/Write               :  1107.439 ms
file           : POPULATE_READ            :    80.413 ms
file           : POPULATE_WRITE           :   857.622 ms
hugetlbfs      : Read                     :   355.607 ms
hugetlbfs      : Write                    :   355.729 ms
hugetlbfs      : Read/Write               :   356.127 ms
hugetlbfs      : POPULATE_READ            :   354.585 ms
hugetlbfs      : POPULATE_WRITE           :   355.138 ms
**************************************************
2 MiB MAP_SHARED:
**************************************************
Anon 4 KiB     : Read                     :     0.394 ms
Anon 4 KiB     : Write                    :     0.348 ms
Anon 4 KiB     : Read/Write               :     0.400 ms
Anon 4 KiB     : POPULATE_READ            :     0.326 ms
Anon 4 KiB     : POPULATE_WRITE           :     0.273 ms
Anon 2 MiB     : Read                     :     0.030 ms
Anon 2 MiB     : Write                    :     0.030 ms
Anon 2 MiB     : Read/Write               :     0.030 ms
Anon 2 MiB     : POPULATE_READ            :     0.030 ms
Anon 2 MiB     : POPULATE_WRITE           :     0.030 ms
Memfd 4 KiB    : Read                     :     0.412 ms
Memfd 4 KiB    : Write                    :     0.372 ms
Memfd 4 KiB    : Read/Write               :     0.419 ms
Memfd 4 KiB    : POPULATE_READ            :     0.343 ms
Memfd 4 KiB    : POPULATE_WRITE           :     0.288 ms
Memfd 4 KiB    : FALLOCATE                :     0.137 ms
Memfd 4 KiB    : FALLOCATE+Read           :     0.446 ms
Memfd 4 KiB    : FALLOCATE+Write          :     0.330 ms
Memfd 4 KiB    : FALLOCATE+Read/Write     :     0.454 ms
Memfd 4 KiB    : FALLOCATE+POPULATE_READ  :     0.379 ms
Memfd 4 KiB    : FALLOCATE+POPULATE_WRITE :     0.268 ms
Memfd 2 MiB    : Read                     :     0.030 ms
Memfd 2 MiB    : Write                    :     0.030 ms
Memfd 2 MiB    : Read/Write               :     0.030 ms
Memfd 2 MiB    : POPULATE_READ            :     0.030 ms
Memfd 2 MiB    : POPULATE_WRITE           :     0.030 ms
Memfd 2 MiB    : FALLOCATE                :     0.030 ms
Memfd 2 MiB    : FALLOCATE+Read           :     0.031 ms
Memfd 2 MiB    : FALLOCATE+Write          :     0.031 ms
Memfd 2 MiB    : FALLOCATE+Read/Write     :     0.031 ms
Memfd 2 MiB    : FALLOCATE+POPULATE_READ  :     0.030 ms
Memfd 2 MiB    : FALLOCATE+POPULATE_WRITE :     0.030 ms
tmpfs          : Read                     :     0.416 ms
tmpfs          : Write                    :     0.369 ms
tmpfs          : Read/Write               :     0.425 ms
tmpfs          : POPULATE_READ            :     0.346 ms
tmpfs          : POPULATE_WRITE           :     0.295 ms
tmpfs          : FALLOCATE                :     0.139 ms
tmpfs          : FALLOCATE+Read           :     0.447 ms
tmpfs          : FALLOCATE+Write          :     0.333 ms
tmpfs          : FALLOCATE+Read/Write     :     0.454 ms
tmpfs          : FALLOCATE+POPULATE_READ  :     0.380 ms
tmpfs          : FALLOCATE+POPULATE_WRITE :     0.272 ms
file           : Read                     :     0.191 ms
file           : Write                    :     0.511 ms
file           : Read/Write               :     0.524 ms
file           : POPULATE_READ            :     0.196 ms
file           : POPULATE_WRITE           :     0.434 ms
file           : FALLOCATE                :     0.004 ms
file           : FALLOCATE+Read           :     0.197 ms
file           : FALLOCATE+Write          :     0.554 ms
file           : FALLOCATE+Read/Write     :     0.480 ms
file           : FALLOCATE+POPULATE_READ  :     0.201 ms
file           : FALLOCATE+POPULATE_WRITE :     0.381 ms
hugetlbfs      : Read                     :     0.030 ms
hugetlbfs      : Write                    :     0.030 ms
hugetlbfs      : Read/Write               :     0.030 ms
hugetlbfs      : POPULATE_READ            :     0.030 ms
hugetlbfs      : POPULATE_WRITE           :     0.030 ms
hugetlbfs      : FALLOCATE                :     0.030 ms
hugetlbfs      : FALLOCATE+Read           :     0.031 ms
hugetlbfs      : FALLOCATE+Write          :     0.031 ms
hugetlbfs      : FALLOCATE+Read/Write     :     0.030 ms
hugetlbfs      : FALLOCATE+POPULATE_READ  :     0.030 ms
hugetlbfs      : FALLOCATE+POPULATE_WRITE :     0.030 ms
**************************************************
4096 MiB MAP_SHARED:
**************************************************
Anon 4 KiB     : Read                     :  1053.090 ms
Anon 4 KiB     : Write                    :   913.642 ms
Anon 4 KiB     : Read/Write               :  1060.350 ms
Anon 4 KiB     : POPULATE_READ            :   893.691 ms
Anon 4 KiB     : POPULATE_WRITE           :   782.885 ms
Anon 2 MiB     : Read                     :   358.553 ms
Anon 2 MiB     : Write                    :   358.419 ms
Anon 2 MiB     : Read/Write               :   357.992 ms
Anon 2 MiB     : POPULATE_READ            :   357.533 ms
Anon 2 MiB     : POPULATE_WRITE           :   357.808 ms
Memfd 4 KiB    : Read                     :  1078.144 ms
Memfd 4 KiB    : Write                    :   942.036 ms
Memfd 4 KiB    : Read/Write               :  1100.391 ms
Memfd 4 KiB    : POPULATE_READ            :   925.829 ms
Memfd 4 KiB    : POPULATE_WRITE           :   804.394 ms
Memfd 4 KiB    : FALLOCATE                :   304.632 ms
Memfd 4 KiB    : FALLOCATE+Read           :  1163.359 ms
Memfd 4 KiB    : FALLOCATE+Write          :   933.186 ms
Memfd 4 KiB    : FALLOCATE+Read/Write     :  1187.304 ms
Memfd 4 KiB    : FALLOCATE+POPULATE_READ  :  1013.660 ms
Memfd 4 KiB    : FALLOCATE+POPULATE_WRITE :   794.560 ms
Memfd 2 MiB    : Read                     :   358.131 ms
Memfd 2 MiB    : Write                    :   358.099 ms
Memfd 2 MiB    : Read/Write               :   358.250 ms
Memfd 2 MiB    : POPULATE_READ            :   357.563 ms
Memfd 2 MiB    : POPULATE_WRITE           :   357.334 ms
Memfd 2 MiB    : FALLOCATE                :   356.735 ms
Memfd 2 MiB    : FALLOCATE+Read           :   358.152 ms
Memfd 2 MiB    : FALLOCATE+Write          :   358.331 ms
Memfd 2 MiB    : FALLOCATE+Read/Write     :   358.018 ms
Memfd 2 MiB    : FALLOCATE+POPULATE_READ  :   357.286 ms
Memfd 2 MiB    : FALLOCATE+POPULATE_WRITE :   357.523 ms
tmpfs          : Read                     :  1087.265 ms
tmpfs          : Write                    :   950.840 ms
tmpfs          : Read/Write               :  1107.567 ms
tmpfs          : POPULATE_READ            :   922.605 ms
tmpfs          : POPULATE_WRITE           :   810.094 ms
tmpfs          : FALLOCATE                :   306.320 ms
tmpfs          : FALLOCATE+Read           :  1169.796 ms
tmpfs          : FALLOCATE+Write          :   933.730 ms
tmpfs          : FALLOCATE+Read/Write     :  1191.610 ms
tmpfs          : FALLOCATE+POPULATE_READ  :  1020.474 ms
tmpfs          : FALLOCATE+POPULATE_WRITE :   798.945 ms
file           : Read                     :   654.101 ms
file           : Write                    :  1259.142 ms
file           : Read/Write               :  1289.509 ms
file           : POPULATE_READ            :   661.642 ms
file           : POPULATE_WRITE           :  1106.816 ms
file           : FALLOCATE                :     1.864 ms
file           : FALLOCATE+Read           :   656.328 ms
file           : FALLOCATE+Write          :  1153.300 ms
file           : FALLOCATE+Read/Write     :  1180.613 ms
file           : FALLOCATE+POPULATE_READ  :   668.347 ms
file           : FALLOCATE+POPULATE_WRITE :   996.143 ms
hugetlbfs      : Read                     :   357.245 ms
hugetlbfs      : Write                    :   357.413 ms
hugetlbfs      : Read/Write               :   357.120 ms
hugetlbfs      : POPULATE_READ            :   356.321 ms
hugetlbfs      : POPULATE_WRITE           :   356.693 ms
hugetlbfs      : FALLOCATE                :   355.927 ms
hugetlbfs      : FALLOCATE+Read           :   357.074 ms
hugetlbfs      : FALLOCATE+Write          :   357.120 ms
hugetlbfs      : FALLOCATE+Read/Write     :   356.983 ms
hugetlbfs      : FALLOCATE+POPULATE_READ  :   356.413 ms
hugetlbfs      : FALLOCATE+POPULATE_WRITE :   356.266 ms
**************************************************

[1] https://lkml.org/lkml/2013/6/27/698

[akpm@linux-foundation.org: coding style fixes]

Link: https://lkml.kernel.org/r/20210419135443.12822-3-david@redhat.comSigned-off-by: NDavid Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rolf Eike Beer <eike-kernel@sf-tec.de>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      4ca9b385
  29. 07 5月, 2021 1 次提交
  31. 14 3月, 2021 1 次提交
    • S
      mm/madvise: replace ptrace attach requirement for process_madvise · 96cfe2c0
      由 Suren Baghdasaryan 提交于 
      process_madvise currently requires ptrace attach capability.
PTRACE_MODE_ATTACH gives one process complete control over another
process.  It effectively removes the security boundary between the two
processes (in one direction).  Granting ptrace attach capability even to a
system process is considered dangerous since it creates an attack surface.
This severely limits the usage of this API.

The operations process_madvise can perform do not affect the correctness
of the operation of the target process; they only affect where the data is
physically located (and therefore, how fast it can be accessed).  What we
want is the ability for one process to influence another process in order
to optimize performance across the entire system while leaving the
security boundary intact.

Replace PTRACE_MODE_ATTACH with a combination of PTRACE_MODE_READ and
CAP_SYS_NICE.  PTRACE_MODE_READ to prevent leaking ASLR metadata and
CAP_SYS_NICE for influencing process performance.

Link: https://lkml.kernel.org/r/20210303185807.2160264-1-surenb@google.comSigned-off-by: NSuren Baghdasaryan <surenb@google.com>
Reviewed-by: NKees Cook <keescook@chromium.org>
Acked-by: NMinchan Kim <minchan@kernel.org>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jeff Vander Stoep <jeffv@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tim Murray <timmurray@google.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: <stable@vger.kernel.org>	[5.10+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      96cfe2c0
  33. 30 1月, 2021 2 次提交
  35. 24 1月, 2021 2 次提交
  37. 16 12月, 2020 2 次提交
  39. 09 12月, 2020 1 次提交
    • M
      mm/madvise: remove racy mm ownership check · a68a0262
      由 Minchan Kim 提交于 
      Jann spotted the security hole due to race of mm ownership check.

If the task is sharing the mm_struct but goes through execve() before
mm_access(), it could skip process_madvise_behavior_valid check.  That
makes *any advice hint* to reach into the remote process.

This patch removes the mm ownership check.  With it, it will lose the
ability that local process could give *any* advice hint with vector
interface for some reason (e.g., performance).  Since there is no
concrete example in upstream yet, it would be better to remove the
abiliity at this moment and need to review when such new advice comes
up.

Fixes: ecb8ac8b ("mm/madvise: introduce process_madvise() syscall: an external memory hinting API")
Reported-by: NJann Horn <jannh@google.com>
Suggested-by: NJann Horn <jannh@google.com>
Signed-off-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a68a0262
  41. 23 11月, 2020 2 次提交
  43. 19 10月, 2020 2 次提交
    • M
      mm/madvise: introduce process_madvise() syscall: an external memory hinting API · ecb8ac8b
      由 Minchan Kim 提交于 
      There is usecase that System Management Software(SMS) want to give a
memory hint like MADV_[COLD|PAGEEOUT] to other processes and in the
case of Android, it is the ActivityManagerService.

The information required to make the reclaim decision is not known to the
app.  Instead, it is known to the centralized userspace
daemon(ActivityManagerService), and that daemon must be able to initiate
reclaim on its own without any app involvement.

To solve the issue, this patch introduces a new syscall
process_madvise(2).  It uses pidfd of an external process to give the
hint.  It also supports vector address range because Android app has
thousands of vmas due to zygote so it's totally waste of CPU and power if
we should call the syscall one by one for each vma.(With testing 2000-vma
syscall vs 1-vector syscall, it showed 15% performance improvement.  I
think it would be bigger in real practice because the testing ran very
cache friendly environment).

Another potential use case for the vector range is to amortize the cost
ofTLB shootdowns for multiple ranges when using MADV_DONTNEED; this could
benefit users like TCP receive zerocopy and malloc implementations.  In
future, we could find more usecases for other advises so let's make it
happens as API since we introduce a new syscall at this moment.  With
that, existing madvise(2) user could replace it with process_madvise(2)
with their own pid if they want to have batch address ranges support
feature.

ince it could affect other process's address range, only privileged
process(PTRACE_MODE_ATTACH_FSCREDS) or something else(e.g., being the same
UID) gives it the right to ptrace the process could use it successfully.
The flag argument is reserved for future use if we need to extend the API.

I think supporting all hints madvise has/will supported/support to
process_madvise is rather risky.  Because we are not sure all hints make
sense from external process and implementation for the hint may rely on
the caller being in the current context so it could be error-prone.  Thus,
I just limited hints as MADV_[COLD|PAGEOUT] in this patch.

If someone want to add other hints, we could hear the usecase and review
it for each hint.  It's safer for maintenance rather than introducing a
buggy syscall but hard to fix it later.

So finally, the API is as follows,

      ssize_t process_madvise(int pidfd, const struct iovec *iovec,
                unsigned long vlen, int advice, unsigned int flags);

    DESCRIPTION
      The process_madvise() system call is used to give advice or directions
      to the kernel about the address ranges from external process as well as
      local process. It provides the advice to address ranges of process
      described by iovec and vlen. The goal of such advice is to improve
      system or application performance.

      The pidfd selects the process referred to by the PID file descriptor
      specified in pidfd. (See pidofd_open(2) for further information)

      The pointer iovec points to an array of iovec structures, defined in
      <sys/uio.h> as:

        struct iovec {
            void *iov_base;         /* starting address */
            size_t iov_len;         /* number of bytes to be advised */
        };

      The iovec describes address ranges beginning at address(iov_base)
      and with size length of bytes(iov_len).

      The vlen represents the number of elements in iovec.

      The advice is indicated in the advice argument, which is one of the
      following at this moment if the target process specified by pidfd is
      external.

        MADV_COLD
        MADV_PAGEOUT

      Permission to provide a hint to external process is governed by a
      ptrace access mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

      The process_madvise supports every advice madvise(2) has if target
      process is in same thread group with calling process so user could
      use process_madvise(2) to extend existing madvise(2) to support
      vector address ranges.

    RETURN VALUE
      On success, process_madvise() returns the number of bytes advised.
      This return value may be less than the total number of requested
      bytes, if an error occurred. The caller should check return value
      to determine whether a partial advice occurred.

FAQ:

Q.1 - Why does any external entity have better knowledge?

Quote from Sandeep

"For Android, every application (including the special SystemServer)
are forked from Zygote.  The reason of course is to share as many
libraries and classes between the two as possible to benefit from the
preloading during boot.

After applications start, (almost) all of the APIs end up calling into
this SystemServer process over IPC (binder) and back to the
application.

In a fully running system, the SystemServer monitors every single
process periodically to calculate their PSS / RSS and also decides
which process is "important" to the user for interactivity.

So, because of how these processes start _and_ the fact that the
SystemServer is looping to monitor each process, it does tend to *know*
which address range of the application is not used / useful.

Besides, we can never rely on applications to clean things up
themselves.  We've had the "hey app1, the system is low on memory,
please trim your memory usage down" notifications for a long time[1].
They rely on applications honoring the broadcasts and very few do.

So, if we want to avoid the inevitable killing of the application and
restarting it, some way to be able to tell the OS about unimportant
memory in these applications will be useful.

- ssp

Q.2 - How to guarantee the race(i.e., object validation) between when
giving a hint from an external process and get the hint from the target
process?

process_madvise operates on the target process's address space as it
exists at the instant that process_madvise is called.  If the space
target process can run between the time the process_madvise process
inspects the target process address space and the time that
process_madvise is actually called, process_madvise may operate on
memory regions that the calling process does not expect.  It's the
responsibility of the process calling process_madvise to close this
race condition.  For example, the calling process can suspend the
target process with ptrace, SIGSTOP, or the freezer cgroup so that it
doesn't have an opportunity to change its own address space before
process_madvise is called.  Another option is to operate on memory
regions that the caller knows a priori will be unchanged in the target
process.  Yet another option is to accept the race for certain
process_madvise calls after reasoning that mistargeting will do no
harm.  The suggested API itself does not provide synchronization.  It
also apply other APIs like move_pages, process_vm_write.

The race isn't really a problem though.  Why is it so wrong to require
that callers do their own synchronization in some manner?  Nobody
objects to write(2) merely because it's possible for two processes to
open the same file and clobber each other's writes --- instead, we tell
people to use flock or something.  Think about mmap.  It never
guarantees newly allocated address space is still valid when the user
tries to access it because other threads could unmap the memory right
before.  That's where we need synchronization by using other API or
design from userside.  It shouldn't be part of API itself.  If someone
needs more fine-grained synchronization rather than process level,
there were two ideas suggested - cookie[2] and anon-fd[3].  Both are
applicable via using last reserved argument of the API but I don't
think it's necessary right now since we have already ways to prevent
the race so don't want to add additional complexity with more
fine-grained optimization model.

To make the API extend, it reserved an unsigned long as last argument
so we could support it in future if someone really needs it.

Q.3 - Why doesn't ptrace work?

Injecting an madvise in the target process using ptrace would not work
for us because such injected madvise would have to be executed by the
target process, which means that process would have to be runnable and
that creates the risk of the abovementioned race and hinting a wrong
VMA.  Furthermore, we want to act the hint in caller's context, not the
callee's, because the callee is usually limited in cpuset/cgroups or
even freezed state so they can't act by themselves quick enough, which
causes more thrashing/kill.  It doesn't work if the target process are
ptraced(e.g., strace, debugger, minidump) because a process can have at
most one ptracer.

[1] https://developer.android.com/topic/performance/memory"

[2] process_getinfo for getting the cookie which is updated whenever
    vma of process address layout are changed - Daniel Colascione -
    https://lore.kernel.org/lkml/20190520035254.57579-1-minchan@kernel.org/T/#m7694416fd179b2066a2c62b5b139b14e3894e224

[3] anonymous fd which is used for the object(i.e., address range)
    validation - Michal Hocko -
    https://lore.kernel.org/lkml/20200120112722.GY18451@dhcp22.suse.cz/

[minchan@kernel.org: fix process_madvise build break for arm64]
  Link: http://lkml.kernel.org/r/20200303145756.GA219683@google.com
[minchan@kernel.org: fix build error for mips of process_madvise]
  Link: http://lkml.kernel.org/r/20200508052517.GA197378@google.com
[akpm@linux-foundation.org: fix patch ordering issue]
[akpm@linux-foundation.org: fix arm64 whoops]
[minchan@kernel.org: make process_madvise() vlen arg have type size_t, per Florian]
[akpm@linux-foundation.org: fix i386 build]
[sfr@canb.auug.org.au: fix syscall numbering]
  Link: https://lkml.kernel.org/r/20200905142639.49fc3f1a@canb.auug.org.au
[sfr@canb.auug.org.au: madvise.c needs compat.h]
  Link: https://lkml.kernel.org/r/20200908204547.285646b4@canb.auug.org.au
[minchan@kernel.org: fix mips build]
  Link: https://lkml.kernel.org/r/20200909173655.GC2435453@google.com
[yuehaibing@huawei.com: remove duplicate header which is included twice]
  Link: https://lkml.kernel.org/r/20200915121550.30584-1-yuehaibing@huawei.com
[minchan@kernel.org: do not use helper functions for process_madvise]
  Link: https://lkml.kernel.org/r/20200921175539.GB387368@google.com
[akpm@linux-foundation.org: pidfd_get_pid() gained an argument]
[sfr@canb.auug.org.au: fix up for "iov_iter: transparently handle compat iovecs in import_iovec"]
  Link: https://lkml.kernel.org/r/20200928212542.468e1fef@canb.auug.org.auSigned-off-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NSuren Baghdasaryan <surenb@google.com>
Reviewed-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Daniel Colascione <dancol@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Dias <joaodias@google.com>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleksandr Natalenko <oleksandr@redhat.com>
Cc: Sandeep Patil <sspatil@google.com>
Cc: SeongJae Park <sj38.park@gmail.com>
Cc: SeongJae Park <sjpark@amazon.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Sonny Rao <sonnyrao@google.com>
Cc: Tim Murray <timmurray@google.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Florian Weimer <fw@deneb.enyo.de>
Cc: <linux-man@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200302193630.68771-3-minchan@kernel.org
Link: http://lkml.kernel.org/r/20200508183320.GA125527@google.com
Link: http://lkml.kernel.org/r/20200622192900.22757-4-minchan@kernel.org
Link: https://lkml.kernel.org/r/20200901000633.1920247-4-minchan@kernel.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      ecb8ac8b
    • M
      mm/madvise: pass mm to do_madvise · 0726b01e
      由 Minchan Kim 提交于 
      Patch series "introduce memory hinting API for external process", v9.

Now, we have MADV_PAGEOUT and MADV_COLD as madvise hinting API.  With
that, application could give hints to kernel what memory range are
preferred to be reclaimed.  However, in some platform(e.g., Android), the
information required to make the hinting decision is not known to the app.
Instead, it is known to a centralized userspace daemon(e.g.,
ActivityManagerService), and that daemon must be able to initiate reclaim
on its own without any app involvement.

To solve the concern, this patch introduces new syscall -
process_madvise(2).  Bascially, it's same with madvise(2) syscall but it
has some differences.

1. It needs pidfd of target process to provide the hint

2. It supports only MADV_{COLD|PAGEOUT|MERGEABLE|UNMEREABLE} at this
   moment.  Other hints in madvise will be opened when there are explicit
   requests from community to prevent unexpected bugs we couldn't support.

3. Only privileged processes can do something for other process's
   address space.

For more detail of the new API, please see "mm: introduce external memory
hinting API" description in this patchset.

This patch (of 3):

In upcoming patches, do_madvise will be called from external process
context so we shouldn't asssume "current" is always hinted process's
task_struct.

Furthermore, we must not access mm_struct via task->mm, but obtain it via
access_mm() once (in the following patch) and only use that pointer [1],
so pass it to do_madvise() as well.  Note the vma->vm_mm pointers are
safe, so we can use them further down the call stack.

And let's pass current->mm as arguments of do_madvise so it shouldn't
change existing behavior but prepare next patch to make review easy.

[vbabka@suse.cz: changelog tweak]
[minchan@kernel.org: use current->mm for io_uring]
  Link: http://lkml.kernel.org/r/20200423145215.72666-1-minchan@kernel.org
[akpm@linux-foundation.org: fix it for upstream changes]
[akpm@linux-foundation.org: whoops]
[rdunlap@infradead.org: add missing includes]
Signed-off-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NSuren Baghdasaryan <surenb@google.com>
Reviewed-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jann Horn <jannh@google.com>
Cc: Tim Murray <timmurray@google.com>
Cc: Daniel Colascione <dancol@google.com>
Cc: Sandeep Patil <sspatil@google.com>
Cc: Sonny Rao <sonnyrao@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: John Dias <joaodias@google.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: SeongJae Park <sj38.park@gmail.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Oleksandr Natalenko <oleksandr@redhat.com>
Cc: SeongJae Park <sjpark@amazon.de>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Florian Weimer <fw@deneb.enyo.de>
Cc: <linux-man@vger.kernel.org>
Link: https://lkml.kernel.org/r/20200901000633.1920247-1-minchan@kernel.org
Link: http://lkml.kernel.org/r/20200622192900.22757-1-minchan@kernel.org
Link: http://lkml.kernel.org/r/20200302193630.68771-2-minchan@kernel.org
Link: http://lkml.kernel.org/r/20200622192900.22757-2-minchan@kernel.org
Link: https://lkml.kernel.org/r/20200901000633.1920247-2-minchan@kernel.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      0726b01e
  45. 17 10月, 2020 2 次提交