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SubjectRe: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0 is loaded
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On 03/16/2016 03:32 AM, Paolo Bonzini wrote:
>
>
> On 15/03/2016 19:27, Andy Lutomirski wrote:
>> On Mon, Mar 14, 2016 at 6:17 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>
>>>
>>> On 11/03/2016 22:33, David Matlack wrote:
>>>>> Is this better than just always keeping the host's XCR0 loaded outside
>>>>> if the KVM interrupts-disabled region?
>>>>
>>>> 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.

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