linux-kernel - Re: [PATCH] x86,kvm: move qemu/guest FPU switching out to vcpu

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Message-ID: <d1aa3e79-7538-6671-dbff-04a3b000bfe5@redhat.com>
Date:   Wed, 15 Nov 2017 09:34:20 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Hildenbrand <david@...hat.com>,
        Rik van Riel <riel@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, rkrcmar@...hat.com, borntraeger@...ibm.com
Subject: Re: [PATCH] x86,kvm: move qemu/guest FPU switching out to vcpu_run

On 14/11/2017 20:40, David Hildenbrand wrote:
> I think we should check all get/put_fpu callers if they need
> preempt_disable().
> 
> E.g. em_fxrstor() needs disabled preemption as we temporarily
> save + restore some host register (via fxsave + fxrstor) under some
> circumstances that are not saved/restored when switching to/back from
> another process. We should double check.

Rik may correct me, but I believe that you don't need
preempt_disable/enable because preempt notifiers do this for you.

Paolo