[PATCH 2/3] kvm: x86: do not use KVM_REQ_EVENT for APICv interrupt injection

[Paolo Bonzini]

Since bf9f6ac8d749 ("KVM: Update Posted-Interrupts Descriptor when vCPU
is blocked", 2015-09-18) the posted interrupt descriptor is checked
unconditionally for PIR.ON.  Therefore we don't need KVM_REQ_EVENT to
trigger the scan and, if NMIs or SMIs are not involved, we can avoid
the complicated event injection path.

However, there is a race between vmx_deliver_posted_interrupt and
vcpu_enter_guest.  Fix it by disabling interrupts before vcpu->mode is
set to IN_GUEST_MODE.

Calling kvm_vcpu_kick if PIR.ON=1 is also useless, though it has been
there since APICv was introduced.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/lapic.c | 2 --
 arch/x86/kvm/vmx.c   | 8 +++++---
 arch/x86/kvm/x86.c   | 9 +++++++--
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 63a442aefc12..be8b7ad56dd1 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -356,8 +356,6 @@ void kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir)
 	struct kvm_lapic *apic = vcpu->arch.apic;
 
 	__kvm_apic_update_irr(pir, apic->regs);
-
-	kvm_make_request(KVM_REQ_EVENT, vcpu);
 }
 EXPORT_SYMBOL_GPL(kvm_apic_update_irr);
 
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index b33eee395b00..207b9aa32915 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4844,9 +4844,11 @@ static void vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector)
 	if (pi_test_and_set_pir(vector, &vmx->pi_desc))
 		return;
 
-	r = pi_test_and_set_on(&vmx->pi_desc);
-	kvm_make_request(KVM_REQ_EVENT, vcpu);
-	if (r || !kvm_vcpu_trigger_posted_interrupt(vcpu))
+	/* If a previous notification has sent the IPI, nothing to do.  */
+	if (pi_test_and_set_on(&vmx->pi_desc))
+		return;
+
+	if (!kvm_vcpu_trigger_posted_interrupt(vcpu))
 		kvm_vcpu_kick(vcpu);
 }
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3ee8a91a78c3..604cfbfc5bee 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6658,6 +6658,13 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	kvm_x86_ops->prepare_guest_switch(vcpu);
 	if (vcpu->fpu_active)
 		kvm_load_guest_fpu(vcpu);
+
+	/*
+	 * Disable IRQs before setting IN_GUEST_MODE, so that
+	 * posted interrupts with vcpu->mode == IN_GUEST_MODE
+	 * always result in virtual interrupt delivery.
+	 */
+	local_irq_disable();
 	vcpu->mode = IN_GUEST_MODE;
 
 	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
@@ -6671,8 +6678,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	 */
 	smp_mb__after_srcu_read_unlock();
 
-	local_irq_disable();
-
 	if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests
 	    || need_resched() || signal_pending(current)) {
 		vcpu->mode = OUTSIDE_GUEST_MODE;
-- 
1.8.3.1