Re: [Xen-devel] [PATCH RFC 7/9] xen: Handle resumed instruction based on previous mem_event reply

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.07.14 at 11:34, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 07/03/2014 12:22 PM, Jan Beulich wrote:
>>>>> On 03.07.14 at 11:12, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> An example that kept appearing with Xen 4.3 and Firefox in our test
>>> environment was: divsd xmm0, qword ptr [0x21c290]
>> 
>> And what's so special about it? Just that there's a better chance of it
>> raising #XM? And why would divss (which is SSE, not SSE2) or vdivsd
>> (AVX) not have similar problems?
> 
> Nothing is particularly special about it, apart from the fact that it
> caused our hypervisor to print out:
> 
> Emulation failed @ 001b:21107d: f2 0f 5e 05 90 c2 21 00 8b 4d
> 
> and Firefox crashed. Indeed, I agree with Andrew that this looks like a
> bug in Xen's emulator, however rather than treating each case
> individually and risk random application crashes with instructions we
> missed, we decided to, for our purposes, treat this as a class of cases
> that can be handled in the same way regardless of the specific instruction.

Which is even more of an argument to extend the emulator we
have rather than introducing half a new one. And of course, with
the goal you have, just won't get away with implementing just the
instructions you have seen being used - you (or someone else) just
have to go through and implement _all_ known instructions. Quite
a bit of a job, I know...

Jan


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