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  1. 08 6月, 2010 1 次提交
  3. 09 4月, 2009 1 次提交
  5. 31 3月, 2009 1 次提交
  7. 02 3月, 2009 1 次提交
    • J
      xen: deal with virtually mapped percpu data · 9976b39b
      由 Jeremy Fitzhardinge 提交于 
      The virtually mapped percpu space causes us two problems:

 - for hypercalls which take an mfn, we need to do a full pagetable
   walk to convert the percpu va into an mfn, and

 - when a hypercall requires a page to be mapped RO via all its aliases,
   we need to make sure its RO in both the percpu mapping and in the
   linear mapping

This primarily affects the gdt and the vcpu info structure.
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Xen-devel <xen-devel@lists.xensource.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Tejun Heo <htejun@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      9976b39b
  9. 05 2月, 2009 1 次提交
    • J
      x86: don't apply __supported_pte_mask to non-present ptes · b534816b
      由 Jeremy Fitzhardinge 提交于 
      On an x86 system which doesn't support global mappings,
__supported_pte_mask has _PAGE_GLOBAL clear, to make sure it never
appears in the PTE.  pfn_pte() and so on will enforce it with:

static inline pte_t pfn_pte(unsigned long page_nr, pgprot_t pgprot)
{
	return __pte((((phys_addr_t)page_nr << PAGE_SHIFT) |
		      pgprot_val(pgprot)) & __supported_pte_mask);
}

However, we overload _PAGE_GLOBAL with _PAGE_PROTNONE on non-present
ptes to distinguish them from swap entries.  However, applying
__supported_pte_mask indiscriminately will clear the bit and corrupt the
pte.

I guess the best fix is to only apply __supported_pte_mask to present
ptes.  This seems like the right solution to me, as it means we can
completely ignore the issue of overlaps between the present pte bits and
the non-present pte-as-swap entry use of the bits.

__supported_pte_mask contains the set of flags we support on the
current hardware.  We also use bits in the pte for things like
logically present ptes with no permissions, and swap entries for
swapped out pages.  We should only apply __supported_pte_mask to
present ptes, because otherwise we may destroy other information being
stored in the ptes.
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
      b534816b
  11. 17 12月, 2008 1 次提交
  13. 23 10月, 2008 3 次提交
  15. 14 9月, 2008 1 次提交
  17. 23 7月, 2008 1 次提交
    • V
      x86: consolidate header guards · 77ef50a5
      由 Vegard Nossum 提交于 
      This patch is the result of an automatic script that consolidates the
format of all the headers in include/asm-x86/.

The format:

1. No leading underscore. Names with leading underscores are reserved.
2. Pathname components are separated by two underscores. So we can
   distinguish between mm_types.h and mm/types.h.
3. Everything except letters and numbers are turned into single
   underscores.
Signed-off-by: NVegard Nossum <vegard.nossum@gmail.com>
      77ef50a5
  19. 22 7月, 2008 1 次提交
    • J
      x86: rename PTE_MASK to PTE_PFN_MASK · 59438c9f
      由 Jeremy Fitzhardinge 提交于 
      Rusty, in his peevish way, complained that macros defining constants
should have a name which somewhat accurately reflects the actual
purpose of the constant.

Aside from the fact that PTE_MASK gives no clue as to what's actually
being masked, and is misleadingly similar to the functionally entirely
different PMD_MASK, PUD_MASK and PGD_MASK, I don't really see what the
problem is.

But if this patch silences the incessent noise, then it will have
achieved its goal (TODO: write test-case).
Signed-off-by: NJeremy Fitzhardinge <jeremy@goop.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      59438c9f
  21. 16 7月, 2008 2 次提交
  23. 24 6月, 2008 1 次提交
  25. 27 5月, 2008 2 次提交
  27. 23 5月, 2008 1 次提交
  29. 20 5月, 2008 1 次提交
  31. 25 4月, 2008 3 次提交
  33. 30 1月, 2008 1 次提交
  35. 27 7月, 2007 1 次提交
  37. 18 7月, 2007 1 次提交
    • J
      xen: Core Xen implementation · 5ead97c8
      由 Jeremy Fitzhardinge 提交于 
      This patch is a rollup of all the core pieces of the Xen
implementation, including:
 - booting and setup
 - pagetable setup
 - privileged instructions
 - segmentation
 - interrupt flags
 - upcalls
 - multicall batching

BOOTING AND SETUP

The vmlinux image is decorated with ELF notes which tell the Xen
domain builder what the kernel's requirements are; the domain builder
then constructs the address space accordingly and starts the kernel.

Xen has its own entrypoint for the kernel (contained in an ELF note).
The ELF notes are set up by xen-head.S, which is included into head.S.
In principle it could be linked separately, but it seems to provoke
lots of binutils bugs.

Because the domain builder starts the kernel in a fairly sane state
(32-bit protected mode, paging enabled, flat segments set up), there's
not a lot of setup needed before starting the kernel proper.  The main
steps are:
  1. Install the Xen paravirt_ops, which is simply a matter of a
     structure assignment.
  2. Set init_mm to use the Xen-supplied pagetables (analogous to the
     head.S generated pagetables in a native boot).
  3. Reserve address space for Xen, since it takes a chunk at the top
     of the address space for its own use.
  4. Call start_kernel()

PAGETABLE SETUP

Once we hit the main kernel boot sequence, it will end up calling back
via paravirt_ops to set up various pieces of Xen specific state.  One
of the critical things which requires a bit of extra care is the
construction of the initial init_mm pagetable.  Because Xen places
tight constraints on pagetables (an active pagetable must always be
valid, and must always be mapped read-only to the guest domain), we
need to be careful when constructing the new pagetable to keep these
constraints in mind.  It turns out that the easiest way to do this is
use the initial Xen-provided pagetable as a template, and then just
insert new mappings for memory where a mapping doesn't already exist.

This means that during pagetable setup, it uses a special version of
xen_set_pte which ignores any attempt to remap a read-only page as
read-write (since Xen will map its own initial pagetable as RO), but
lets other changes to the ptes happen, so that things like NX are set
properly.

PRIVILEGED INSTRUCTIONS AND SEGMENTATION

When the kernel runs under Xen, it runs in ring 1 rather than ring 0.
This means that it is more privileged than user-mode in ring 3, but it
still can't run privileged instructions directly.  Non-performance
critical instructions are dealt with by taking a privilege exception
and trapping into the hypervisor and emulating the instruction, but
more performance-critical instructions have their own specific
paravirt_ops.  In many cases we can avoid having to do any hypercalls
for these instructions, or the Xen implementation is quite different
from the normal native version.

The privileged instructions fall into the broad classes of:
  Segmentation: setting up the GDT and the GDT entries, LDT,
     TLS and so on.  Xen doesn't allow the GDT to be directly
     modified; all GDT updates are done via hypercalls where the new
     entries can be validated.  This is important because Xen uses
     segment limits to prevent the guest kernel from damaging the
     hypervisor itself.
  Traps and exceptions: Xen uses a special format for trap entrypoints,
     so when the kernel wants to set an IDT entry, it needs to be
     converted to the form Xen expects.  Xen sets int 0x80 up specially
     so that the trap goes straight from userspace into the guest kernel
     without going via the hypervisor.  sysenter isn't supported.
  Kernel stack: The esp0 entry is extracted from the tss and provided to
     Xen.
  TLB operations: the various TLB calls are mapped into corresponding
     Xen hypercalls.
  Control registers: all the control registers are privileged.  The most
     important is cr3, which points to the base of the current pagetable,
     and we handle it specially.

Another instruction we treat specially is CPUID, even though its not
privileged.  We want to control what CPU features are visible to the
rest of the kernel, and so CPUID ends up going into a paravirt_op.
Xen implements this mainly to disable the ACPI and APIC subsystems.

INTERRUPT FLAGS

Xen maintains its own separate flag for masking events, which is
contained within the per-cpu vcpu_info structure.  Because the guest
kernel runs in ring 1 and not 0, the IF flag in EFLAGS is completely
ignored (and must be, because even if a guest domain disables
interrupts for itself, it can't disable them overall).

(A note on terminology: "events" and interrupts are effectively
synonymous.  However, rather than using an "enable flag", Xen uses a
"mask flag", which blocks event delivery when it is non-zero.)

There are paravirt_ops for each of cli/sti/save_fl/restore_fl, which
are implemented to manage the Xen event mask state.  The only thing
worth noting is that when events are unmasked, we need to explicitly
see if there's a pending event and call into the hypervisor to make
sure it gets delivered.

UPCALLS

Xen needs a couple of upcall (or callback) functions to be implemented
by each guest.  One is the event upcalls, which is how events
(interrupts, effectively) are delivered to the guests.  The other is
the failsafe callback, which is used to report errors in either
reloading a segment register, or caused by iret.  These are
implemented in i386/kernel/entry.S so they can jump into the normal
iret_exc path when necessary.

MULTICALL BATCHING

Xen provides a multicall mechanism, which allows multiple hypercalls
to be issued at once in order to mitigate the cost of trapping into
the hypervisor.  This is particularly useful for context switches,
since the 4-5 hypercalls they would normally need (reload cr3, update
TLS, maybe update LDT) can be reduced to one.  This patch implements a
generic batching mechanism for hypercalls, which gets used in many
places in the Xen code.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>
Cc: Ian Pratt <ian.pratt@xensource.com>
Cc: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Cc: Adrian Bunk <bunk@stusta.de>
      5ead97c8