Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0 is loaded

From	Paolo Bonzini <pbonzini@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0 is loaded
Date	2016-03-16 13:10 +0100
Message-ID	<rdir0-kr-15@gated-at.bofh.it> (permalink)
References	(3 earlier) <rbCWR-3YT-1@gated-at.bofh.it> <rcAzD-4e2-9@gated-at.bofh.it> <rd1Tb-5O3-3@gated-at.bofh.it> <rd2YV-6xB-3@gated-at.bofh.it> <rdaMP-3gF-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 16/03/2016 04:55, Xiao Guangrong wrote:
>>>>>
>>>>> Probably not. AFAICT KVM does not rely on it being loaded outside that
>>>>> region. xsetbv isn't insanely expensive, is it? Maybe to minimize the
>>>>> time spent with interrupts disabled it was put outside.
>>>>>
>>>>> I do like that your solution would be contained to KVM.
>>>>
>>>> I agree with Andy.  We do want a fix for recent kernels because of the
>>>> !eager_fpu case that Guangrong mentioned.
> 
> Relying on interrupt is not easy as XCR0 can not be automatically
> saved/loaded by VMCS... Once interrupt happens, it will use guest's XCR0 anyway.

Right, that's why an xsetbv while interrupts are disabled is appealing.

Paolo

Thread

[PATCH 0/1] KVM: x86: using the fpu in interrupt context with a guest's xcr0 David Matlack <dmatlack@google.com> - 2016-03-11 21:50 +0100
  [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0 is loaded David Matlack <dmatlack@google.com> - 2016-03-11 21:50 +0100
    Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0  is loaded Andy Lutomirski <luto@amacapital.net> - 2016-03-11 22:20 +0100
      Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0  is loaded David Matlack <dmatlack@google.com> - 2016-03-11 22:40 +0100
        Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0  is loaded Paolo Bonzini <pbonzini@redhat.com> - 2016-03-14 14:20 +0100
          Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0  is loaded Andy Lutomirski <luto@amacapital.net> - 2016-03-15 19:30 +0100
            Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0  is loaded Paolo Bonzini <pbonzini@redhat.com> - 2016-03-15 20:40 +0100
              Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0  is loaded Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2016-03-16 05:00 +0100
                Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0  is loaded Paolo Bonzini <pbonzini@redhat.com> - 2016-03-16 13:10 +0100
  Re: [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a  guest's xcr0 Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2016-03-14 08:50 +0100
    Re: [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a  guest's xcr0 David Matlack <dmatlack@google.com> - 2016-03-15 20:10 +0100
      Re: [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a  guest's xcr0 Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2016-03-16 04:50 +0100
        Re: [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a  guest's xcr0 Andy Lutomirski <luto@amacapital.net> - 2016-03-16 04:50 +0100
          Re: [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a  guest's xcr0 David Matlack <dmatlack@google.com> - 2016-03-16 18:20 +0100
        Re: [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a  guest's xcr0 David Matlack <dmatlack@google.com> - 2016-03-16 18:10 +0100

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