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KVM: VMX: Don't do full kick when triggering posted interrupt "fails"

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Replace the full "kick" with just the "wake" in the fallback path when
triggering a virtual interrupt via a posted interrupt fails because the
guest is not IN_GUEST_MODE.  If the guest transitions into guest mode
between the check and the kick, then it's guaranteed to see the pending
interrupt as KVM syncs the PIR to IRR (and onto GUEST_RVI) after setting
IN_GUEST_MODE.  Kicking the guest in this case is nothing more than an
unnecessary VM-Exit (and host IRQ).

Opportunistically update comments to explain the various ordering rules
and barriers at play.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211208015236.1616697-17-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-12-08 01:52:26 +00:00 committed by Paolo Bonzini
parent 782f64558d
commit 0f65a9d337
2 changed files with 7 additions and 6 deletions
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4
arch/x86/kvm/vmx/vmx.c
View File

@ -3998,7 +3998,7 @@ static int vmx_deliver_nested_posted_interrupt(struct kvm_vcpu *vcpu,
/* the PIR and ON have been set by L1. */
if (!kvm_vcpu_trigger_posted_interrupt(vcpu, true))
kvm_vcpu_kick(vcpu);
kvm_vcpu_wake_up(vcpu);
return 0;
}
return -1;
@ -4036,7 +4036,7 @@ static int vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector)
* posted interrupt "fails" because vcpu->mode != IN_GUEST_MODE.
*/
if (!kvm_vcpu_trigger_posted_interrupt(vcpu, false))
kvm_vcpu_kick(vcpu);
kvm_vcpu_wake_up(vcpu);
return 0;
}

9
arch/x86/kvm/x86.c
View File

@ -9978,10 +9978,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
smp_mb__after_srcu_read_unlock();
/*
* This handles the case where a posted interrupt was
* notified with kvm_vcpu_kick. Assigned devices can
* use the POSTED_INTR_VECTOR even if APICv is disabled,
* so do it even if APICv is disabled on this vCPU.
* Process pending posted interrupts to handle the case where the
* notification IRQ arrived in the host, or was never sent (because the
* target vCPU wasn't running). Do this regardless of the vCPU's APICv
* status, KVM doesn't update assigned devices when APICv is inhibited,
* i.e. they can post interrupts even if APICv is temporarily disabled.
*/
if (kvm_lapic_enabled(vcpu))
static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);