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

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Message-ID: <980be73e-828d-d844-d2ab-ea91ec2844e6@redhat.com>
Date:   Wed, 15 Nov 2017 10:23:46 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Paolo Bonzini <pbonzini@...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 15.11.2017 09:34, Paolo Bonzini wrote:
> 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.
> 

Seems to boil down to what Wanpeng Li asked about preempt notifiers in
response to v2.

-- 

Thanks,

David / dhildenb