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Date: Thu, 18 Feb 2010 17:29:35 +0100 From: Joerg Roedel <joerg.roedel@....com> To: Avi Kivity <avi@...hat.com> CC: Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 09/10] KVM: SVM: Make lazy FPU switching work with nested svm On Thu, Feb 18, 2010 at 04:32:02PM +0200, Avi Kivity wrote: > On 02/18/2010 01:38 PM, Joerg Roedel wrote: > >TDB. > > > > ... > > >@@ -973,6 +973,7 @@ static void svm_decache_cr4_guest_bits(struct kvm_vcpu *vcpu) > > > > static void update_cr0_intercept(struct vcpu_svm *svm) > > { > >+ struct vmcb *vmcb = svm->vmcb; > > ulong gcr0 = svm->vcpu.arch.cr0; > > u64 *hcr0 =&svm->vmcb->save.cr0; > > > >@@ -984,11 +985,25 @@ static void update_cr0_intercept(struct vcpu_svm *svm) > > > > > > if (gcr0 == *hcr0&& svm->vcpu.fpu_active) { > >- svm->vmcb->control.intercept_cr_read&= ~INTERCEPT_CR0_MASK; > >- svm->vmcb->control.intercept_cr_write&= ~INTERCEPT_CR0_MASK; > >+ vmcb->control.intercept_cr_read&= ~INTERCEPT_CR0_MASK; > >+ vmcb->control.intercept_cr_write&= ~INTERCEPT_CR0_MASK; > >+ if (is_nested(svm)) { > >+ struct vmcb *hsave = svm->nested.hsave; > >+ > >+ hsave->control.intercept_cr_read&= ~INTERCEPT_CR0_MASK; > >+ hsave->control.intercept_cr_write&= ~INTERCEPT_CR0_MASK; > >+ vmcb->control.intercept_cr_read |= svm->nested.intercept_cr_read; > >+ vmcb->control.intercept_cr_write |= svm->nested.intercept_cr_write; > > Why are the last two lines needed? Because we don't know if the l1 hypervisor wants to intercept cr0. In this case we need this intercept to stay enabled. > >+ } > > } else { > > svm->vmcb->control.intercept_cr_read |= INTERCEPT_CR0_MASK; > > svm->vmcb->control.intercept_cr_write |= INTERCEPT_CR0_MASK; > >+ if (is_nested(svm)) { > >+ struct vmcb *hsave = svm->nested.hsave; > >+ > >+ hsave->control.intercept_cr_read |= INTERCEPT_CR0_MASK; > >+ hsave->control.intercept_cr_write |= INTERCEPT_CR0_MASK; > >+ } > > } > > } > > Maybe it's better to call update_cr0_intercept() after a vmexit > instead, to avoid this repetition, and since the if () may take a > different branch for the nested guest and guest cr0. Thinking again about it I am not sure if this is needed at all. At vmexit emulation we call svm_set_cr0 which itself calls update_cr0_intercept. I'll try this. Joerg -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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