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  1. 09 9月, 2017 1 次提交
    • Z
      mm: thp: check pmd migration entry in common path · 84c3fc4e
      由 Zi Yan 提交于 
      When THP migration is being used, memory management code needs to handle
pmd migration entries properly.  This patch uses !pmd_present() or
is_swap_pmd() (depending on whether pmd_none() needs separate code or
not) to check pmd migration entries at the places where a pmd entry is
present.

Since pmd-related code uses split_huge_page(), split_huge_pmd(),
pmd_trans_huge(), pmd_trans_unstable(), or
pmd_none_or_trans_huge_or_clear_bad(), this patch:

1. adds pmd migration entry split code in split_huge_pmd(),

2. takes care of pmd migration entries whenever pmd_trans_huge() is present,

3. makes pmd_none_or_trans_huge_or_clear_bad() pmd migration entry aware.

Since split_huge_page() uses split_huge_pmd() and pmd_trans_unstable()
is equivalent to pmd_none_or_trans_huge_or_clear_bad(), we do not change
them.

Until this commit, a pmd entry should be:
1. pointing to a pte page,
2. is_swap_pmd(),
3. pmd_trans_huge(),
4. pmd_devmap(), or
5. pmd_none().
Signed-off-by: NZi Yan <zi.yan@cs.rutgers.edu>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Nellans <dnellans@nvidia.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      84c3fc4e
  3. 07 9月, 2017 5 次提交
    • H
      mm: hugetlb: clear target sub-page last when clearing huge page · c79b57e4
      由 Huang Ying 提交于 
      Huge page helps to reduce TLB miss rate, but it has higher cache
footprint, sometimes this may cause some issue.  For example, when
clearing huge page on x86_64 platform, the cache footprint is 2M.  But
on a Xeon E5 v3 2699 CPU, there are 18 cores, 36 threads, and only 45M
LLC (last level cache).  That is, in average, there are 2.5M LLC for
each core and 1.25M LLC for each thread.

If the cache pressure is heavy when clearing the huge page, and we clear
the huge page from the begin to the end, it is possible that the begin
of huge page is evicted from the cache after we finishing clearing the
end of the huge page.  And it is possible for the application to access
the begin of the huge page after clearing the huge page.

To help the above situation, in this patch, when we clear a huge page,
the order to clear sub-pages is changed.  In quite some situation, we
can get the address that the application will access after we clear the
huge page, for example, in a page fault handler.  Instead of clearing
the huge page from begin to end, we will clear the sub-pages farthest
from the the sub-page to access firstly, and clear the sub-page to
access last.  This will make the sub-page to access most cache-hot and
sub-pages around it more cache-hot too.  If we cannot know the address
the application will access, the begin of the huge page is assumed to be
the the address the application will access.

With this patch, the throughput increases ~28.3% in vm-scalability
anon-w-seq test case with 72 processes on a 2 socket Xeon E5 v3 2699
system (36 cores, 72 threads).  The test case creates 72 processes, each
process mmap a big anonymous memory area and writes to it from the begin
to the end.  For each process, other processes could be seen as other
workload which generates heavy cache pressure.  At the same time, the
cache miss rate reduced from ~33.4% to ~31.7%, the IPC (instruction per
cycle) increased from 0.56 to 0.74, and the time spent in user space is
reduced ~7.9%

Christopher Lameter suggests to clear bytes inside a sub-page from end
to begin too.  But tests show no visible performance difference in the
tests.  May because the size of page is small compared with the cache
size.

Thanks Andi Kleen to propose to use address to access to determine the
order of sub-pages to clear.

The hugetlbfs access address could be improved, will do that in another
patch.

[ying.huang@intel.com: improve readability of clear_huge_page()]
  Link: http://lkml.kernel.org/r/20170830051842.1397-1-ying.huang@intel.com
Link: http://lkml.kernel.org/r/20170815014618.15842-1-ying.huang@intel.comSuggested-by: NAndi Kleen <andi.kleen@intel.com>
Signed-off-by: N"Huang, Ying" <ying.huang@intel.com>
Acked-by: NJan Kara <jack@suse.cz>
Reviewed-by: NMichal Hocko <mhocko@suse.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Nadia Yvette Chambers <nyc@holomorphy.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shaohua Li <shli@fb.com>
Cc: Christopher Lameter <cl@linux.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      c79b57e4
    • H
      mm, swap: VMA based swap readahead · ec560175
      由 Huang Ying 提交于 
      The swap readahead is an important mechanism to reduce the swap in
latency.  Although pure sequential memory access pattern isn't very
popular for anonymous memory, the space locality is still considered
valid.

In the original swap readahead implementation, the consecutive blocks in
swap device are readahead based on the global space locality estimation.
But the consecutive blocks in swap device just reflect the order of page
reclaiming, don't necessarily reflect the access pattern in virtual
memory.  And the different tasks in the system may have different access
patterns, which makes the global space locality estimation incorrect.

In this patch, when page fault occurs, the virtual pages near the fault
address will be readahead instead of the swap slots near the fault swap
slot in swap device.  This avoid to readahead the unrelated swap slots.
At the same time, the swap readahead is changed to work on per-VMA from
globally.  So that the different access patterns of the different VMAs
could be distinguished, and the different readahead policy could be
applied accordingly.  The original core readahead detection and scaling
algorithm is reused, because it is an effect algorithm to detect the
space locality.

The test and result is as follow,

Common test condition
=====================

Test Machine: Xeon E5 v3 (2 sockets, 72 threads, 32G RAM) Swap device:
NVMe disk

Micro-benchmark with combined access pattern
============================================

vm-scalability, sequential swap test case, 4 processes to eat 50G
virtual memory space, repeat the sequential memory writing until 300
seconds.  The first round writing will trigger swap out, the following
rounds will trigger sequential swap in and out.

At the same time, run vm-scalability random swap test case in
background, 8 processes to eat 30G virtual memory space, repeat the
random memory write until 300 seconds.  This will trigger random swap-in
in the background.

This is a combined workload with sequential and random memory accessing
at the same time.  The result (for sequential workload) is as follow,

			Base		Optimized
			----		---------
throughput		345413 KB/s	414029 KB/s (+19.9%)
latency.average		97.14 us	61.06 us (-37.1%)
latency.50th		2 us		1 us
latency.60th		2 us		1 us
latency.70th		98 us		2 us
latency.80th		160 us		2 us
latency.90th		260 us		217 us
latency.95th		346 us		369 us
latency.99th		1.34 ms		1.09 ms
ra_hit%			52.69%		99.98%

The original swap readahead algorithm is confused by the background
random access workload, so readahead hit rate is lower.  The VMA-base
readahead algorithm works much better.

Linpack
=======

The test memory size is bigger than RAM to trigger swapping.

			Base		Optimized
			----		---------
elapsed_time		393.49 s	329.88 s (-16.2%)
ra_hit%			86.21%		98.82%

The score of base and optimized kernel hasn't visible changes.  But the
elapsed time reduced and readahead hit rate improved, so the optimized
kernel runs better for startup and tear down stages.  And the absolute
value of readahead hit rate is high, shows that the space locality is
still valid in some practical workloads.

Link: http://lkml.kernel.org/r/20170807054038.1843-4-ying.huang@intel.comSigned-off-by: N"Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Tim Chen <tim.c.chen@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      ec560175
    • H
      mm, THP, swap: make reuse_swap_page() works for THP swapped out · ba3c4ce6
      由 Huang Ying 提交于 
      After supporting to delay THP (Transparent Huge Page) splitting after
swapped out, it is possible that some page table mappings of the THP are
turned into swap entries.  So reuse_swap_page() need to check the swap
count in addition to the map count as before.  This patch done that.

In the huge PMD write protect fault handler, in addition to the page map
count, the swap count need to be checked too, so the page lock need to
be acquired too when calling reuse_swap_page() in addition to the page
table lock.

[ying.huang@intel.com: silence a compiler warning]
  Link: http://lkml.kernel.org/r/87bmnzizjy.fsf@yhuang-dev.intel.com
Link: http://lkml.kernel.org/r/20170724051840.2309-4-ying.huang@intel.comSigned-off-by: N"Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Ross Zwisler <ross.zwisler@intel.com> [for brd.c, zram_drv.c, pmem.c]
Cc: Vishal L Verma <vishal.l.verma@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      ba3c4ce6
    • M
      mm: always flush VMA ranges affected by zap_page_range · 4647706e
      由 Mel Gorman 提交于 
      Nadav Amit report zap_page_range only specifies that the caller protect
the VMA list but does not specify whether it is held for read or write
with callers using either.  madvise holds mmap_sem for read meaning that
a parallel zap operation can unmap PTEs which are then potentially
skipped by madvise which potentially returns with stale TLB entries
present.  While the API could be extended, it would be a difficult API
to use.  This patch causes zap_page_range() to always consider flushing
the full affected range.  For small ranges or sparsely populated
mappings, this may result in one additional spurious TLB flush.  For
larger ranges, it is possible that the TLB has already been flushed and
the overhead is negligible.  Either way, this approach is safer overall
and avoids stale entries being present when madvise returns.

This can be illustrated with the following program provided by Nadav
Amit and slightly modified.  With the patch applied, it has an exit code
of 0 indicating a stale TLB entry did not leak to userspace.

---8<---

volatile int sync_step = 0;
volatile char *p;

static inline unsigned long rdtsc()
{
	unsigned long hi, lo;
	__asm__ __volatile__ ("rdtsc" : "=a"(lo), "=d"(hi));
	 return lo | (hi << 32);
}

static inline void wait_rdtsc(unsigned long cycles)
{
	unsigned long tsc = rdtsc();

	while (rdtsc() - tsc < cycles);
}

void *big_madvise_thread(void *ign)
{
	sync_step = 1;
	while (sync_step != 2);
	madvise((void*)p, PAGE_SIZE * N_PAGES, MADV_DONTNEED);
}

int main(void)
{
	pthread_t aux_thread;

	p = mmap(0, PAGE_SIZE * N_PAGES, PROT_READ|PROT_WRITE,
		 MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);

	memset((void*)p, 8, PAGE_SIZE * N_PAGES);

	pthread_create(&aux_thread, NULL, big_madvise_thread, NULL);
	while (sync_step != 1);

	*p = 8;		// Cache in TLB
	sync_step = 2;
	wait_rdtsc(100000);
	madvise((void*)p, PAGE_SIZE, MADV_DONTNEED);
	printf("data: %d (%s)\n", *p, (*p == 8 ? "stale, broken" : "cleared, fine"));
	return *p == 8 ? -1 : 0;
}
---8<---

Link: http://lkml.kernel.org/r/20170725101230.5v7gvnjmcnkzzql3@techsingularity.netSigned-off-by: NMel Gorman <mgorman@suse.de>
Reported-by: NNadav Amit <nadav.amit@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      4647706e
    • R
      mm: add vm_insert_mixed_mkwrite() · b2770da6
      由 Ross Zwisler 提交于 
      When servicing mmap() reads from file holes the current DAX code
allocates a page cache page of all zeroes and places the struct page
pointer in the mapping->page_tree radix tree.  This has three major
drawbacks:

1) It consumes memory unnecessarily. For every 4k page that is read via
   a DAX mmap() over a hole, we allocate a new page cache page. This
   means that if you read 1GiB worth of pages, you end up using 1GiB of
   zeroed memory.

2) It is slower than using a common zero page because each page fault
   has more work to do. Instead of just inserting a common zero page we
   have to allocate a page cache page, zero it, and then insert it.

3) The fact that we had to check for both DAX exceptional entries and
   for page cache pages in the radix tree made the DAX code more
   complex.

This series solves these issues by following the lead of the DAX PMD
code and using a common 4k zero page instead.  This reduces memory usage
and decreases latencies for some workloads, and it simplifies the DAX
code, removing over 100 lines in total.

This patch (of 5):

To be able to use the common 4k zero page in DAX we need to have our PTE
fault path look more like our PMD fault path where a PTE entry can be
marked as dirty and writeable as it is first inserted rather than
waiting for a follow-up dax_pfn_mkwrite() => finish_mkwrite_fault()
call.

Right now we can rely on having a dax_pfn_mkwrite() call because we can
distinguish between these two cases in do_wp_page():

	case 1: 4k zero page => writable DAX storage
	case 2: read-only DAX storage => writeable DAX storage

This distinction is made by via vm_normal_page().  vm_normal_page()
returns false for the common 4k zero page, though, just as it does for
DAX ptes.  Instead of special casing the DAX + 4k zero page case we will
simplify our DAX PTE page fault sequence so that it matches our DAX PMD
sequence, and get rid of the dax_pfn_mkwrite() helper.  We will instead
use dax_iomap_fault() to handle write-protection faults.

This means that insert_pfn() needs to follow the lead of
insert_pfn_pmd() and allow us to pass in a 'mkwrite' flag.  If 'mkwrite'
is set insert_pfn() will do the work that was previously done by
wp_page_reuse() as part of the dax_pfn_mkwrite() call path.

Link: http://lkml.kernel.org/r/20170724170616.25810-2-ross.zwisler@linux.intel.comSigned-off-by: NRoss Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      b2770da6
  5. 01 9月, 2017 1 次提交
    • J
      dax: update to new mmu_notifier semantic · a4d1a885
      由 Jérôme Glisse 提交于 
      Replace all mmu_notifier_invalidate_page() calls by *_invalidate_range()
and make sure it is bracketed by calls to *_invalidate_range_start()/end().

Note that because we can not presume the pmd value or pte value we have
to assume the worst and unconditionaly report an invalidation as
happening.
Signed-off-by: NJérôme Glisse <jglisse@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Bernhard Held <berny156@gmx.de>
Cc: Adam Borowski <kilobyte@angband.pl>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: axie <axie@amd.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a4d1a885
  7. 19 8月, 2017 2 次提交
    • M
      mm, oom: fix potential data corruption when oom_reaper races with writer · 6b31d595
      由 Michal Hocko 提交于 
      Wenwei Tao has noticed that our current assumption that the oom victim
is dying and never doing any visible changes after it dies, and so the
oom_reaper can tear it down, is not entirely true.

__task_will_free_mem consider a task dying when SIGNAL_GROUP_EXIT is set
but do_group_exit sends SIGKILL to all threads _after_ the flag is set.
So there is a race window when some threads won't have
fatal_signal_pending while the oom_reaper could start unmapping the
address space.  Moreover some paths might not check for fatal signals
before each PF/g-u-p/copy_from_user.

We already have a protection for oom_reaper vs.  PF races by checking
MMF_UNSTABLE.  This has been, however, checked only for kernel threads
(use_mm users) which can outlive the oom victim.  A simple fix would be
to extend the current check in handle_mm_fault for all tasks but that
wouldn't be sufficient because the current check assumes that a kernel
thread would bail out after EFAULT from get_user*/copy_from_user and
never re-read the same address which would succeed because the PF path
has established page tables already.  This seems to be the case for the
only existing use_mm user currently (virtio driver) but it is rather
fragile in general.

This is even more fragile in general for more complex paths such as
generic_perform_write which can re-read the same address more times
(e.g.  iov_iter_copy_from_user_atomic to fail and then
iov_iter_fault_in_readable on retry).

Therefore we have to implement MMF_UNSTABLE protection in a robust way
and never make a potentially corrupted content visible.  That requires
to hook deeper into the PF path and check for the flag _every time_
before a pte for anonymous memory is established (that means all
!VM_SHARED mappings).

The corruption can be triggered artificially
(http://lkml.kernel.org/r/201708040646.v746kkhC024636@www262.sakura.ne.jp)
but there doesn't seem to be any real life bug report.  The race window
should be quite tight to trigger most of the time.

Link: http://lkml.kernel.org/r/20170807113839.16695-3-mhocko@kernel.org
Fixes: aac45363 ("mm, oom: introduce oom reaper")
Signed-off-by: NMichal Hocko <mhocko@suse.com>
Reported-by: NWenwei Tao <wenwei.tww@alibaba-inc.com>
Tested-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andrea Argangeli <andrea@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      6b31d595
    • M
      mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS · 5b53a6ea
      由 Michal Hocko 提交于 
      Tetsuo Handa has noticed that MMF_UNSTABLE SIGBUS path in
handle_mm_fault causes a lockdep splat

  Out of memory: Kill process 1056 (a.out) score 603 or sacrifice child
  Killed process 1056 (a.out) total-vm:4268108kB, anon-rss:2246048kB, file-rss:0kB, shmem-rss:0kB
  a.out (1169) used greatest stack depth: 11664 bytes left
  DEBUG_LOCKS_WARN_ON(depth <= 0)
  ------------[ cut here ]------------
  WARNING: CPU: 6 PID: 1339 at kernel/locking/lockdep.c:3617 lock_release+0x172/0x1e0
  CPU: 6 PID: 1339 Comm: a.out Not tainted 4.13.0-rc3-next-20170803+ #142
  Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
  RIP: 0010:lock_release+0x172/0x1e0
  Call Trace:
     up_read+0x1a/0x40
     __do_page_fault+0x28e/0x4c0
     do_page_fault+0x30/0x80
     page_fault+0x28/0x30

The reason is that the page fault path might have dropped the mmap_sem
and returned with VM_FAULT_RETRY.  MMF_UNSTABLE check however rewrites
the error path to VM_FAULT_SIGBUS and we always expect mmap_sem taken in
that path.  Fix this by taking mmap_sem when VM_FAULT_RETRY is held in
the MMF_UNSTABLE path.

We cannot simply add VM_FAULT_SIGBUS to the existing error code because
all arch specific page fault handlers and g-u-p would have to learn a
new error code combination.

Link: http://lkml.kernel.org/r/20170807113839.16695-2-mhocko@kernel.org
Fixes: 3f70dc38 ("mm: make sure that kthreads will not refault oom reaped memory")
Reported-by: NTetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Andrea Argangeli <andrea@kernel.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Wenwei Tao <wenwei.tww@alibaba-inc.com>
Cc: <stable@vger.kernel.org>	[4.9+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      5b53a6ea
  9. 11 8月, 2017 2 次提交
    • M
      mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem · 99baac21
      由 Minchan Kim 提交于 
      Nadav reported parallel MADV_DONTNEED on same range has a stale TLB
problem and Mel fixed it[1] and found same problem on MADV_FREE[2].

Quote from Mel Gorman:
 "The race in question is CPU 0 running madv_free and updating some PTEs
  while CPU 1 is also running madv_free and looking at the same PTEs.
  CPU 1 may have writable TLB entries for a page but fail the pte_dirty
  check (because CPU 0 has updated it already) and potentially fail to
  flush.

  Hence, when madv_free on CPU 1 returns, there are still potentially
  writable TLB entries and the underlying PTE is still present so that a
  subsequent write does not necessarily propagate the dirty bit to the
  underlying PTE any more. Reclaim at some unknown time at the future
  may then see that the PTE is still clean and discard the page even
  though a write has happened in the meantime. I think this is possible
  but I could have missed some protection in madv_free that prevents it
  happening."

This patch aims for solving both problems all at once and is ready for
other problem with KSM, MADV_FREE and soft-dirty story[3].

TLB batch API(tlb_[gather|finish]_mmu] uses [inc|dec]_tlb_flush_pending
and mmu_tlb_flush_pending so that when tlb_finish_mmu is called, we can
catch there are parallel threads going on.  In that case, forcefully,
flush TLB to prevent for user to access memory via stale TLB entry
although it fail to gather page table entry.

I confirmed this patch works with [4] test program Nadav gave so this
patch supersedes "mm: Always flush VMA ranges affected by zap_page_range
v2" in current mmotm.

NOTE:

This patch modifies arch-specific TLB gathering interface(x86, ia64,
s390, sh, um).  It seems most of architecture are straightforward but
s390 need to be careful because tlb_flush_mmu works only if
mm->context.flush_mm is set to non-zero which happens only a pte entry
really is cleared by ptep_get_and_clear and friends.  However, this
problem never changes the pte entries but need to flush to prevent
memory access from stale tlb.

[1] http://lkml.kernel.org/r/20170725101230.5v7gvnjmcnkzzql3@techsingularity.net
[2] http://lkml.kernel.org/r/20170725100722.2dxnmgypmwnrfawp@suse.de
[3] http://lkml.kernel.org/r/BD3A0EBE-ECF4-41D4-87FA-C755EA9AB6BD@gmail.com
[4] https://patchwork.kernel.org/patch/9861621/

[minchan@kernel.org: decrease tlb flush pending count in tlb_finish_mmu]
  Link: http://lkml.kernel.org/r/20170808080821.GA31730@bbox
Link: http://lkml.kernel.org/r/20170802000818.4760-7-namit@vmware.comSigned-off-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NNadav Amit <namit@vmware.com>
Reported-by: NNadav Amit <namit@vmware.com>
Reported-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      99baac21
    • M
      mm: refactor TLB gathering API · 56236a59
      由 Minchan Kim 提交于 
      This patch is a preparatory patch for solving race problems caused by
TLB batch.  For that, we will increase/decrease TLB flush pending count
of mm_struct whenever tlb_[gather|finish]_mmu is called.

Before making it simple, this patch separates architecture specific part
and rename it to arch_tlb_[gather|finish]_mmu and generic part just
calls it.

It shouldn't change any behavior.

Link: http://lkml.kernel.org/r/20170802000818.4760-5-namit@vmware.comSigned-off-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NNadav Amit <namit@vmware.com>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      56236a59
  11. 03 8月, 2017 1 次提交
    • M
      mm, mprotect: flush TLB if potentially racing with a parallel reclaim leaving stale TLB entries · 3ea27719
      由 Mel Gorman 提交于 
      Nadav Amit identified a theoritical race between page reclaim and
mprotect due to TLB flushes being batched outside of the PTL being held.

He described the race as follows:

        CPU0                            CPU1
        ----                            ----
                                        user accesses memory using RW PTE
                                        [PTE now cached in TLB]
        try_to_unmap_one()
        ==> ptep_get_and_clear()
        ==> set_tlb_ubc_flush_pending()
                                        mprotect(addr, PROT_READ)
                                        ==> change_pte_range()
                                        ==> [ PTE non-present - no flush ]

                                        user writes using cached RW PTE
        ...

        try_to_unmap_flush()

The same type of race exists for reads when protecting for PROT_NONE and
also exists for operations that can leave an old TLB entry behind such
as munmap, mremap and madvise.

For some operations like mprotect, it's not necessarily a data integrity
issue but it is a correctness issue as there is a window where an
mprotect that limits access still allows access.  For munmap, it's
potentially a data integrity issue although the race is massive as an
munmap, mmap and return to userspace must all complete between the
window when reclaim drops the PTL and flushes the TLB.  However, it's
theoritically possible so handle this issue by flushing the mm if
reclaim is potentially currently batching TLB flushes.

Other instances where a flush is required for a present pte should be ok
as either the page lock is held preventing parallel reclaim or a page
reference count is elevated preventing a parallel free leading to
corruption.  In the case of page_mkclean there isn't an obvious path
that userspace could take advantage of without using the operations that
are guarded by this patch.  Other users such as gup as a race with
reclaim looks just at PTEs.  huge page variants should be ok as they
don't race with reclaim.  mincore only looks at PTEs.  userfault also
should be ok as if a parallel reclaim takes place, it will either fault
the page back in or read some of the data before the flush occurs
triggering a fault.

Note that a variant of this patch was acked by Andy Lutomirski but this
was for the x86 parts on top of his PCID work which didn't make the 4.13
merge window as expected.  His ack is dropped from this version and
there will be a follow-on patch on top of PCID that will include his
ack.

[akpm@linux-foundation.org: tweak comments]
[akpm@linux-foundation.org: fix spello]
Link: http://lkml.kernel.org/r/20170717155523.emckq2esjro6hf3z@suse.deReported-by: NNadav Amit <nadav.amit@gmail.com>
Signed-off-by: NMel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: <stable@vger.kernel.org>	[v4.4+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      3ea27719
  13. 13 7月, 2017 1 次提交
  15. 11 7月, 2017 1 次提交
  17. 07 7月, 2017 2 次提交
  19. 19 6月, 2017 1 次提交
    • H
      mm: larger stack guard gap, between vmas · 1be7107f
      由 Hugh Dickins 提交于 
      Stack guard page is a useful feature to reduce a risk of stack smashing
into a different mapping. We have been using a single page gap which
is sufficient to prevent having stack adjacent to a different mapping.
But this seems to be insufficient in the light of the stack usage in
userspace. E.g. glibc uses as large as 64kB alloca() in many commonly
used functions. Others use constructs liks gid_t buffer[NGROUPS_MAX]
which is 256kB or stack strings with MAX_ARG_STRLEN.

This will become especially dangerous for suid binaries and the default
no limit for the stack size limit because those applications can be
tricked to consume a large portion of the stack and a single glibc call
could jump over the guard page. These attacks are not theoretical,
unfortunatelly.

Make those attacks less probable by increasing the stack guard gap
to 1MB (on systems with 4k pages; but make it depend on the page size
because systems with larger base pages might cap stack allocations in
the PAGE_SIZE units) which should cover larger alloca() and VLA stack
allocations. It is obviously not a full fix because the problem is
somehow inherent, but it should reduce attack space a lot.

One could argue that the gap size should be configurable from userspace,
but that can be done later when somebody finds that the new 1MB is wrong
for some special case applications.  For now, add a kernel command line
option (stack_guard_gap) to specify the stack gap size (in page units).

Implementation wise, first delete all the old code for stack guard page:
because although we could get away with accounting one extra page in a
stack vma, accounting a larger gap can break userspace - case in point,
a program run with "ulimit -S -v 20000" failed when the 1MB gap was
counted for RLIMIT_AS; similar problems could come with RLIMIT_MLOCK
and strict non-overcommit mode.

Instead of keeping gap inside the stack vma, maintain the stack guard
gap as a gap between vmas: using vm_start_gap() in place of vm_start
(or vm_end_gap() in place of vm_end if VM_GROWSUP) in just those few
places which need to respect the gap - mainly arch_get_unmapped_area(),
and and the vma tree's subtree_gap support for that.
Original-patch-by: NOleg Nesterov <oleg@redhat.com>
Original-patch-by: NMichal Hocko <mhocko@suse.com>
Signed-off-by: NHugh Dickins <hughd@google.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Tested-by: Helge Deller <deller@gmx.de> # parisc
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      1be7107f
  21. 03 6月, 2017 1 次提交
    • R
      mm: avoid spurious 'bad pmd' warning messages · d0f0931d
      由 Ross Zwisler 提交于 
      When the pmd_devmap() checks were added by 5c7fb56e ("mm, dax:
dax-pmd vs thp-pmd vs hugetlbfs-pmd") to add better support for DAX huge
pages, they were all added to the end of if() statements after existing
pmd_trans_huge() checks.  So, things like:

  -       if (pmd_trans_huge(*pmd))
  +       if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd))

When further checks were added after pmd_trans_unstable() checks by
commit 7267ec00 ("mm: postpone page table allocation until we have
page to map") they were also added at the end of the conditional:

  +       if (pmd_trans_unstable(fe->pmd) || pmd_devmap(*fe->pmd))

This ordering is fine for pmd_trans_huge(), but doesn't work for
pmd_trans_unstable().  This is because DAX huge pages trip the bad_pmd()
check inside of pmd_none_or_trans_huge_or_clear_bad() (called by
pmd_trans_unstable()), which prints out a warning and returns 1.  So, we
do end up doing the right thing, but only after spamming dmesg with
suspicious looking messages:

  mm/pgtable-generic.c:39: bad pmd ffff8808daa49b88(84000001006000a5)

Reorder these checks in a helper so that pmd_devmap() is checked first,
avoiding the error messages, and add a comment explaining why the
ordering is important.

Fixes: commit 7267ec00 ("mm: postpone page table allocation until we have page to map")
Link: http://lkml.kernel.org/r/20170522215749.23516-1-ross.zwisler@linux.intel.comSigned-off-by: NRoss Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Cc: Pawel Lebioda <pawel.lebioda@intel.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Xiong Zhou <xzhou@redhat.com>
Cc: Eryu Guan <eguan@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      d0f0931d
  23. 29 3月, 2017 1 次提交
  25. 10 3月, 2017 2 次提交
  27. 02 3月, 2017 4 次提交
  29. 25 2月, 2017 8 次提交
  31. 23 2月, 2017 7 次提交