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SubjectRe: [PATCH v2 3/3] KVM: SVM: Add irqchip_split() checks before enabling AVIC
2017-09-12 10:42-0500, 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').
>
> 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..a7b96e7 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1176,7 +1176,6 @@ static void avic_init_vmcb(struct vcpu_svm *svm)
> vmcb->control.avic_physical_id = ppa & AVIC_HPA_MASK;
> vmcb->control.avic_physical_id |= AVIC_MAX_PHYSICAL_ID_COUNT;
> vmcb->control.int_ctl |= AVIC_ENABLE_MASK;
> - svm->vcpu.arch.apicv_active = true;
> }
>
> static void init_vmcb(struct vcpu_svm *svm)
> @@ -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 (!kvm_vcpu_apicv_active(&svm->vcpu)) {
> + pr_debug("%s: Disable AVIC due to non-split irqchip.\n",
> + __func__);

We need to have an extra condition just because of this print ...
I removed the print altogether when applying -- I thought more about
that and it was aimed at people who wonder why AVIC was suddenly
disabled and it's unlikely that they will enable a debug message without
already knowing the reason,

thanks.

> @@ -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)
> {

A close contender was pr_info_once() here:

if (avic && !irqchip_split(vcpu->kvm))
pr_info_once(...)

> - 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 (!kvm_vcpu_apicv_active(&svm->vcpu))
> return;
>
> vmcb->control.int_ctl &= ~AVIC_ENABLE_MASK;
> --
> 1.8.3.1
>

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