From: Rik van Riel <riel@redhat.com>
To: "quan.xu04@gmail.com" <quan.xu04@gmail.com>, pbonzini@redhat.com
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
david@redhat.com, borntraeger@de.ibm.com, tglx@linutronix.de,
rkrcmar@redhat.com, Quan Xu <quan.xu0@gmail.com>
Subject: Re: [PATCH 1/2] x86,kvm: move qemu/guest FPU switching out to vcpu_run
Date: Wed, 15 Nov 2017 09:43:01 -0500 [thread overview]
Message-ID: <1510756981.21121.291.camel@redhat.com> (raw)
In-Reply-To: <2e83dd3f-8f03-03ac-45e0-f2fae1d17013@gmail.com>
On Wed, 2017-11-15 at 14:53 +0800, quan.xu04@gmail.com wrote:
>
> On 2017/11/15 05:54, riel@redhat.com wrote:
> > From: Rik van Riel <riel@redhat.com>
> >
> > 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?
next prev parent reply other threads:[~2017-11-15 14:43 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-14 21:54 [PATCH v2 0/2] x86,kvm: move qemu/guest FPU switching out to kvm_arch_vcpu_ioctl_run riel
2017-11-14 21:54 ` [PATCH 1/2] x86,kvm: move qemu/guest FPU switching out to vcpu_run riel
2017-11-15 0:47 ` Wanpeng Li
2017-11-15 3:03 ` Rik van Riel
2017-11-15 4:33 ` Wanpeng Li
2017-11-15 14:40 ` Rik van Riel
2017-11-16 5:54 ` Wanpeng Li
2017-11-15 6:53 ` quan.xu04
2017-11-15 14:43 ` Rik van Riel [this message]
2017-11-15 15:09 ` Paolo Bonzini
2017-11-16 2:50 ` Quan Xu
2017-11-16 4:21 ` Rik van Riel
2017-11-16 5:06 ` Quan Xu
2017-11-16 10:21 ` Paolo Bonzini
2017-11-16 12:12 ` Quan Xu
2017-11-16 12:18 ` Paolo Bonzini
2017-11-16 13:35 ` Quan Xu
2017-11-16 13:39 ` Paolo Bonzini
[not found] ` <d67cef62-3165-50cd-36e8-be7c555dc79e@gmail.com>
2017-11-16 17:50 ` Paolo Bonzini
2017-11-17 2:54 ` Quan Xu
2017-11-14 21:54 ` [PATCH 2/2] x86,kvm: remove KVM emulator get_fpu / put_fpu riel
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