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Date: Wed, 16 Mar 2016 13:01:12 +0100 From: Paolo Bonzini <pbonzini@...hat.com> To: Xiao Guangrong <guangrong.xiao@...ux.intel.com>, Andy Lutomirski <luto@...capital.net> Cc: David Matlack <dmatlack@...gle.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>, kvm list <kvm@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>, Andrew Lutomirski <luto@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, Eric Northup <digitaleric@...gle.com> Subject: Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0 is loaded 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
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