[lkml]   [2017]   [Nov]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 1/2] x86,kvm: move qemu/guest FPU switching out to vcpu_run
On Wed, 2017-11-15 at 14:53 +0800, wrote:
> On 2017/11/15 05:54, wrote:
> > From: Rik van Riel <>
> >
> > 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?

 \ /
  Last update: 2017-11-15 15:43    [W:0.127 / U:1.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site