[PATCH v3 10/26] KVM: SVM: Signal AVIC doorbell iff vCPU is in guest mode

Sean Christopherson
2021-12-08T01:55:14Z

Signal the AVIC doorbell iff the vCPU is running in the guest. If the vCPU
is not IN_GUEST_MODE, it's guaranteed to pick up any pending IRQs on the
next VMRUN, which unconditionally processes the vIRR.

Add comments to document the logic.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/avic.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index d7132a4551a2..e2e4e9f04458 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -672,9 +672,22 @@ int svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
return -1;

kvm_lapic_set_irr(vec, vcpu->arch.apic);
+
+ /*
+ * Pairs with the smp_mb_*() after setting vcpu->guest_mode in
+ * vcpu_enter_guest() to ensure the write to the vIRR is ordered before
+ * the read of guest_mode, which guarantees that either VMRUN will see
+ * and process the new vIRR entry, or that the below code will signal
+ * the doorbell if the vCPU is already running in the guest.
+ */
smp_mb__after_atomic();

- if (avic_vcpu_is_running(vcpu)) {
+ /*
+ * Signal the doorbell to tell hardware to inject the IRQ if the vCPU
+ * is in the guest. If the vCPU is not in the guest, hardware will
+ * automatically process AVIC interrupts at VMRUN.
+ */
+ if (vcpu->mode == IN_GUEST_MODE) {
int cpu = READ_ONCE(vcpu->cpu);

/*
@@ -688,8 +701,13 @@ int svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
if (cpu != get_cpu())
wrmsrl(SVM_AVIC_DOORBELL, kvm_cpu_get_apicid(cpu));
put_cpu();
- } else
+ } else {
+ /*
+ * Wake the vCPU if it was blocking. KVM will then detect the
+ * pending IRQ when checking if the vCPU has a wake event.
+ */
kvm_vcpu_wake_up(vcpu);
+ }

return 0;
}
--
2.34.1.400.ga245620fadb-goog