Re: [PATCH 1/2] x86,kvm: move qemu/guest FPU switching out to vcpu_run

[Paolo Bonzini]

On 15/11/2017 15:43, Rik van Riel wrote:
>> Rik, be careful with VM migration. with you patch, I don't think youÂ
>> could load fpu/xstate
>> ÂÂ 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?

Nothing as far as I can see. :)

Paolo