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SubjectRe: [PATCH v2 11/15] svm: Temporary deactivate AVIC during ExtINT handling
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On 15.08.19 18:25, Suthikulpanit, Suravee wrote:
> AMD AVIC does not support ExtINT. Therefore, AVIC must be temporary
> deactivated and fall back to using legacy interrupt injection via vINTR
> and interrupt window.
>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
> arch/x86/kvm/svm.c | 49 +++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 45 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index cfa4b13..4690351 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -384,6 +384,7 @@ struct amd_svm_iommu_ir {
> static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
> static void svm_flush_tlb(struct kvm_vcpu *vcpu, bool invalidate_gpa);
> static void svm_complete_interrupts(struct vcpu_svm *svm);
> +static void svm_request_activate_avic(struct kvm_vcpu *vcpu);
> static bool svm_get_enable_apicv(struct kvm *kvm);
> static inline void avic_post_state_restore(struct kvm_vcpu *vcpu);
>
> @@ -4494,6 +4495,15 @@ static int interrupt_window_interception(struct vcpu_svm *svm)
> {
> kvm_make_request(KVM_REQ_EVENT, &svm->vcpu);
> svm_clear_vintr(svm);
> +
> + /*
> + * For AVIC, the only reason to end up here is ExtINTs.
> + * In this case AVIC was temporarily disabled for
> + * requesting the IRQ window and we have to re-enable it.
> + */
> + if (svm_get_enable_apicv(svm->vcpu.kvm))
> + svm_request_activate_avic(&svm->vcpu);

Would it make sense to add a trace point here and to the other call
sites, so that it becomes obvious in a trace when and why exactly avic
was active/inactive?

The trace point could add additional information on the why.

> +
> svm->vmcb->control.int_ctl &= ~V_IRQ_MASK;
> mark_dirty(svm->vmcb, VMCB_INTR);
> ++svm->vcpu.stat.irq_window_exits;
> @@ -5181,7 +5191,33 @@ static void svm_hwapic_isr_update(struct kvm_vcpu *vcpu, int max_isr)
> {
> }
>
> -/* Note: Currently only used by Hyper-V. */
> +static bool is_avic_active(struct vcpu_svm *svm)
> +{
> + return (svm_get_enable_apicv(svm->vcpu.kvm) &&
> + svm->vmcb->control.int_ctl & AVIC_ENABLE_MASK);
> +}
> +
> +static void svm_request_activate_avic(struct kvm_vcpu *vcpu)
> +{
> + struct vcpu_svm *svm = to_svm(vcpu);
> +
> + if (!lapic_in_kernel(vcpu) || is_avic_active(svm))
> + return;
> +
> + kvm_make_apicv_activate_request(vcpu);
> +}
> +
> +static void svm_request_deactivate_avic(struct kvm_vcpu *vcpu)
> +{
> + struct vcpu_svm *svm = to_svm(vcpu);
> +
> + if (!lapic_in_kernel(vcpu) || !is_avic_active(svm))
> + return;
> +
> + /* Request temporary deactivate apicv */
> + kvm_make_apicv_deactivate_request(vcpu, false);
> +}
> +
> static void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
> @@ -5522,9 +5558,6 @@ static void enable_irq_window(struct kvm_vcpu *vcpu)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
>
> - if (kvm_vcpu_apicv_active(vcpu))
> - return;
> -
> /*
> * In case GIF=0 we can't rely on the CPU to tell us when GIF becomes
> * 1, because that's a separate STGI/VMRUN intercept. The next time we
> @@ -5534,6 +5567,14 @@ static void enable_irq_window(struct kvm_vcpu *vcpu)
> * window under the assumption that the hardware will set the GIF.
> */
> if ((vgif_enabled(svm) || gif_set(svm)) && nested_svm_intr(svm)) {
> + /*
> + * IRQ window is not needed when AVIC is enabled,
> + * unless we have pending ExtINT since it cannot be injected
> + * via AVIC. In such case, we need to temporarily disable AVIC,
> + * and fallback to injecting IRQ via V_IRQ.
> + */
> + if (kvm_vcpu_apicv_active(vcpu))
> + svm_request_deactivate_avic(&svm->vcpu);

Did you test AVIC with nesting? Did you actually run across this issue
there?


Alex

> svm_set_vintr(svm);
> svm_inject_irq(svm, 0x0);
> }
>

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