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KVM: SVM: Signal AVIC doorbell iff vCPU is in guest mode

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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>
Message-Id: <20211208015236.1616697-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-12-08 01:52:20 +00:00 committed by Paolo Bonzini
parent c3e8abf0f3
commit 31f251d4dd
1 changed files with 20 additions and 2 deletions
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22
arch/x86/kvm/svm/avic.c
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@ -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;
}