Xen devel - Aug 2010 - [PATCH] xen svm: fix PAUSE instruction intercept

Hi!

Attached patch moves PAUSE instruction intercept handling
into svm_vmexit_do_pause() analogous to the other instruction
intercepts.

In svm_vmexit_do_pause() update the instruction pointer.
This fixes strange PAUSE intercepts on UP guests.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>

P.S.: This bug has been found with nested virtualization.

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---to satisfy European Law for business letters:
Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach b. Muenchen
Geschaeftsfuehrer: Alberto Bozzo, Andrew Bowd
Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen
Registergericht Muenchen, HRB Nr. 43632


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>>> On 12.08.10 at 11:22, Christoph Egger
<Christoph.Egger@amd.com> wrote:
> In svm_vmexit_do_pause() update the instruction pointer.
> This fixes strange PAUSE intercepts on UP guests.
This won''t work when the instruction needs to actually be decoded:
__get_instruction_length_from_list() strips all prefix bytes from
the byte stream being decoded, and since ''pause'' uses a prefix
the
actual opcode comparison will never produce a match.

Even in the case that CPUs supporting the pause filter would always
support nextrip I think that the special case minimally deserves a
code comment to that effect, but perhaps even warrants an
ASSERT() or BUG_ON().

Jan


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On Thursday 12 August 2010 12:07:54 Jan Beulich wrote:
> >>> On 12.08.10 at 11:22, Christoph Egger
<Christoph.Egger@amd.com> wrote:
> >
> > In svm_vmexit_do_pause() update the instruction pointer.
> > This fixes strange PAUSE intercepts on UP guests.
>
> This won''t work when the instruction needs to actually be decoded:
> __get_instruction_length_from_list() strips all prefix bytes from
> the byte stream being decoded, and since ''pause'' uses a
prefix the
> actual opcode comparison will never produce a match.
Thank you for pointing this out. New attached version fixes this.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>
> Even in the case that CPUs supporting the pause filter would always
> support nextrip I think that the special case minimally deserves a
> code comment to that effect, but perhaps even warrants an
> ASSERT() or BUG_ON().
This is true for real hardware but not necessarily when it comes
to nested virtualization, because you emulate SVM features
in software.

Christoph


-- 
---to satisfy European Law for business letters:
Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach b. Muenchen
Geschaeftsfuehrer: Alberto Bozzo, Andrew Bowd
Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen
Registergericht Muenchen, HRB Nr. 43632


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