Re: [Xen-devel] Re: issues with movnti emulation

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 20/11/08 17:16, "Tim Deegan" <Tim.Deegan@xxxxxxxxxx> wrote:

> At 17:13 +0000 on 20 Nov (1227201181), Keir Fraser wrote:
>> I think the issue is that I did a bad backport to 3.3. The 'case 0xc3'
>> should be under twobyte_special_insn rather than twobyte_insn, right? The
>> two separate paths got merged into one in xen-unstable.
>> 
>> Of course this data corruption ought only to happen in cases where we'd
>> previously have failed an mmio emulation (and hence probably killed the
>> guest kernel?).
> 
> A more likely culprit is that some OSes use movnti to zero pages that
> used to be pagetables; when we couldn't emulate it we just (correctly)
> unshadowed those pages.

Yes, you're probably right. I wonder if we are relying on emulation failures
to inform unshadowing at all often? We might have to revisit constraining
x86_emulate() when called by shadow code, do you think?

 -- Keir



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