Re: [PATCH v2][uq/master] kvm: x86: Save/restore FPU OP, IP and DP

Avi Kivity
2011-06-19T12:59:01Z

On 06/15/2011 04:17 PM, Jan Kiszka wrote:
> These FPU states are properly maintained by KVM but not yet by TCG. So
> far we unconditionally set them to 0 in the guest which may cause
> state corruptions, though not with modern guests.
>
> To avoid breaking backward migration, use a conditional subsection that
> is only written if any of the three fields is non-zero. The guest's
> FNINIT clears them frequently, and cleared IA32_MISC_ENABLE MSR[2]
> reduces the probability of non-zero values further so that this
> subsection is not expected to restrict migration in any common scenario.

Thanks, applied to uq/master. A test migration showed that the
subsection in fact did not show up.

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