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Subject: Re: [PATCH 1/2] x86,kvm: move qemu/guest FPU switching out to
 vcpu_run
To: Quan Xu <quan.xu0@gmail.com>, Rik van Riel <riel@redhat.com>,
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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <9ba2d4c1-0781-419e-ddeb-77e0494583d2@redhat.com>
Date: Thu, 16 Nov 2017 11:21:39 +0100
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On 16/11/2017 06:06, Quan Xu wrote:
> when vcpu thread is scheduled out, the pkru value in
> current->thread.fpu.state may be the host pkru value, instead of
> guest pkru value (of course, this _assumes_ that the pkru is in
> current->thread.fpu.state as well). in this way, the pkru may be a
> coner case.

Rik may correct me, but I think this is not possible.  Preemption is
disabled all the time while PKRU = guest_pkru (which is only during
vmx_vcpu_run).

Context switching will only happen in vcpu_enter_guest() after
preempt_enable() for a preemptible kernel, or in vcpu_run via
cond_resched() for a non-preemptible kernel.

Thanks,

Paolo

> 
> VM migration again, in case,
>            source_host_pkru_value != guest_pkru_value,
>            target_host_pkru_value == guest_pkru_value..
> 
> the pkru status would be inconsistent..