[PATCH v3 16/26] KVM: VMX: Don't do full kick when triggering posted interrupt "fails"

Sean Christopherson
2021-12-08T01:55:34Z

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>
---
arch/x86/kvm/vmx/vmx.c | 4 ++--
arch/x86/kvm/x86.c | 9 +++++----
2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1b8804d93776..fa90eacbf7e2 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3956,7 +3956,7 @@ 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;
@@ -3995,7 +3995,7 @@ static int vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector)
*/
if (vcpu != kvm_get_running_vcpu() &&
!kvm_vcpu_trigger_posted_interrupt(vcpu, false))
- kvm_vcpu_kick(vcpu);
+ kvm_vcpu_wake_up(vcpu);

return 0;
}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4a2341e4ff30..abf99b77883e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9887,10 +9887,11 @@ 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 !kvm_vcpu_apicv_active(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);
--
2.34.1.400.ga245620fadb-goog