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SubjectRe: [PATCH 6/6] svm: Temporary deactivate AVIC during ExtINT handling
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Hi Suravee.

I wonder, how this interacts with Hyper-V SynIC; see comments below.

On 22/03/2019 12.57, 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.
>
> Introduce svm_request_activate/deactivate_avic() helper functions,
> which handle steps required to activate/deactivate AVIC.
>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
> arch/x86/kvm/svm.c | 57 +++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 54 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index f41f34f70dde..84116e689d5f 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -391,6 +391,8 @@ static u8 rsm_ins_bytes[] = "\x0f\xaa";
> 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_vcpu *vcpu);
>
> static int nested_svm_exit_handled(struct vcpu_svm *svm);
> static int nested_svm_intercept(struct vcpu_svm *svm);
> @@ -2109,6 +2111,9 @@ static void avic_set_running(struct kvm_vcpu *vcpu, bool is_run)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
>
> + if (!kvm_vcpu_apicv_active(vcpu))
> + return;
> +
> svm->avic_is_running = is_run;
> if (is_run)
> avic_vcpu_load(vcpu, vcpu->cpu);
> @@ -2356,6 +2361,10 @@ static void svm_vcpu_blocking(struct kvm_vcpu *vcpu)
>
> static void svm_vcpu_unblocking(struct kvm_vcpu *vcpu)
> {
> + if (kvm_check_request(KVM_REQ_APICV_ACTIVATE, vcpu))
> + kvm_vcpu_activate_apicv(vcpu);
> + if (kvm_check_request(KVM_REQ_APICV_DEACTIVATE, vcpu))
> + kvm_vcpu_deactivate_apicv(vcpu);
> avic_set_running(vcpu, true);
> }
>
> @@ -4505,6 +4514,15 @@ 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))
> + svm_request_activate_avic(&svm->vcpu);
> +

Are we sure, we're not accidentally re-enabling AVIC, if it was disabled via
kvm_hv_activate_synic()?


> svm->vmcb->control.int_ctl &= ~V_IRQ_MASK;
> mark_dirty(svm->vmcb, VMCB_INTR);
> ++svm->vcpu.stat.irq_window_exits;
> @@ -5206,6 +5224,34 @@ static void svm_hwapic_isr_update(struct kvm_vcpu *vcpu, int max_isr)
> {
> }
>
> +static bool is_avic_active(struct vcpu_svm *svm)
> +{
> + return (svm_get_enable_apicv(&svm->vcpu) &&
> + 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;
> +
> + avic_setup_access_page(vcpu, false);
> + kvm_make_apicv_activate_request(vcpu->kvm);
> +}
> +
> +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;
> +
> + avic_destroy_access_page(vcpu);

Something like avic_destroy_access_page() is not called, when AVIC is
disabled via kvm_hv_activate_synic().

Is that an oversight in the other code path, is it not needed here,
or am I missing something?


> + kvm_make_apicv_deactivate_request(vcpu->kvm);
> +}
> +
> /* Note: Currently only used by Hyper-V. */

nit: This comment should probably go away, now.

Regards
Jan


> static void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
> {
> @@ -5493,9 +5539,6 @@ 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
> @@ -5505,6 +5548,14 @@ 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);
> svm_set_vintr(svm);
> svm_inject_irq(svm, 0x0);
> }
>

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