On Wed, 2017-11-15 at 14:53 +0800, [email protected] wrote:
>
> On 2017/11/15 05:54, [email protected] wrote:
> > From: Rik van Riel <[email protected]>
> >
> > Currently, every time a VCPU is scheduled out, the host kernel will
> > first save the guest FPU/xstate context, then load the qemu
> > userspace
> > FPU context, only to then immediately save the qemu userspace FPU
> > context back to memory. When scheduling in a VCPU, the same
> > extraneous
> > FPU loads and saves are done.
>
> Rik, be careful with VM migration. with you patch, I don't think you
> could load fpu/xstate
> context accurately after VM migration.
Can you explain why you believe that?
Getting the guest FPU or XSTATE is done under the vcpu->mutex.
This patch switches out guest and userspace FPU/XSTATE under the
vcpu->mutex, and switches it back before releasing the vcpu->mutex.
By the time a KVM_GET_FPU has obtained the vcpu->mutex, the guest
FPU state will be in vcpu->arch.guest_fpu.state, where you expect
it to be.
What am I missing?
From 1584143475626487432@xxx Wed Nov 15 14:42:26 +0000 2017
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