Re: [PATCH] KVM: APIC: avoid instruction emulation for EOI writes

[Avi Kivity <avi@redhat.com>]

On 08/29/2011 02:03 PM, Jan Kiszka wrote:
> >
> >  Just reading the first byte requires a guest page table walk.  This is
> >  probably the highest cost in emulation (which also requires a walk for
> >  the data access).
>
> And what about caching the result of the first walk? Usually, a "sane
> guest" won't have many code pages that issue the EIO.
>

There's no way to know when to invalidate the cache.

We could go a bit further, and cache the the whole thing.  On the first 
exit, do the entire emulation, and remember %rip.  On the second exit, 
if %rip matches, skip directly to kvm_lapic_eoi().

But I don't think it's worth it.  This also has failure modes, and 
really, no guest will ever write to EOI with stosl.

-- 
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