Messages in this thread | | | Date | Fri, 8 Sep 2017 17:53:25 +0200 | From | Radim Krčmář <> | Subject | Re: [PATCH 3/3] KVM: SVM: Add irqchip_split() checks before enabling AVIC |
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2017-09-05 22:39-0500, Suravee Suthikulpanit: > SVM AVIC hardware accelerates guest write to APIC_EOI register > (for edge-trigger interrupt), which means it does not trap to KVM. > > So, only enable SVM AVIC only in split irqchip mode. > (e.g. launching qemu w/ option '-machine kernel_irqchip=split').
Yeah, hacking TMR to get the VM exit could result in future bugs. We have to push split irqchip as the deafult in userspaces with this change.
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com> > Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> > --- > arch/x86/kvm/svm.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > index d1b3eb4..7ce191b 100644 > --- a/arch/x86/kvm/svm.c > +++ b/arch/x86/kvm/svm.c > @@ -1292,7 +1291,7 @@ static void init_vmcb(struct vcpu_svm *svm) > set_intercept(svm, INTERCEPT_PAUSE); > } > > - if (avic) > + if (kvm_vcpu_apicv_active(&svm->vcpu)) > avic_init_vmcb(svm); > /* > @@ -1594,6 +1593,12 @@ static int avic_init_vcpu(struct vcpu_svm *svm) > if (!avic) > return 0; > > + if (!irqchip_split(svm->vcpu.kvm)) {
The other place used kvm_vcpu_apicv_active() instead of checking irqchip_split() directly, so I think it would be better to be consistent and do it here too. I'd also like if this workaround used !irqchip_split() exactly once.
> + pr_debug("%s: Disable AVIC due to non-split irqchip.\n", > + __func__);
There is going to be too much of those. pr_debug_once() would be a better notification. We can also report it in svm_get_enable_apicv().
> + return 0; > + } > + > ret = avic_init_backing_page(&svm->vcpu); > if (ret) > return ret; > @@ -4388,7 +4393,7 @@ static void svm_set_virtual_x2apic_mode(struct kvm_vcpu *vcpu, bool set) > > static bool svm_get_enable_apicv(struct kvm_vcpu *vcpu) > { > - return avic; > + return avic && irqchip_split(vcpu->kvm); > } > > static void svm_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr) > @@ -4405,7 +4410,7 @@ static void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu) > struct vcpu_svm *svm = to_svm(vcpu); > struct vmcb *vmcb = svm->vmcb; > > - if (!avic) > + if (!avic || !irqchip_split(svm->vcpu.kvm))
Seems like we want !kvm_vcpu_apicv_active() here too.
> return; > > vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
(separate bug: refresh should be able to enable avic as well.)
thanks.
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