KVM: nVMX: Morph notification vector IRQ on nested VM-Enter to pending PI

On successful nested VM-Enter, check for pending interrupts and convert
the highest priority interrupt to a pending posted interrupt if it
matches L2's notification vector.  If the vCPU receives a notification
interrupt before nested VM-Enter (assuming L1 disables IRQs before doing
VM-Enter), the pending interrupt (for L1) should be recognized and
processed as a posted interrupt when interrupts become unblocked after
VM-Enter to L2.

This fixes a bug where L1/L2 will get stuck in an infinite loop if L1 is
trying to inject an interrupt into L2 by setting the appropriate bit in
L2's PIR and sending a self-IPI prior to VM-Enter (as opposed to KVM's
method of manually moving the vector from PIR->vIRR/RVI).  KVM will
observe the IPI while the vCPU is in L1 context and so won't immediately
morph it to a posted interrupt for L2.  The pending interrupt will be
seen by vmx_check_nested_events(), cause KVM to force an immediate exit
after nested VM-Enter, and eventually be reflected to L1 as a VM-Exit.
After handling the VM-Exit, L1 will see that L2 has a pending interrupt
in PIR, send another IPI, and repeat until L2 is killed.

Note, posted interrupts require virtual interrupt deliveriy, and virtual
interrupt delivery requires exit-on-interrupt, ergo interrupts will be
unconditionally unmasked on VM-Enter if posted interrupts are enabled.

Fixes: 705699a139 ("KVM: nVMX: Enable nested posted interrupt processing")
Cc: stable@vger.kernel.org
Cc: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200812175129.12172-1-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -494,6 +494,12 @@ static inline void apic_clear_irr(int vec, struct kvm_lapic *apic)
 	}
 }
 
+void kvm_apic_clear_irr(struct kvm_vcpu *vcpu, int vec)
+{
+	apic_clear_irr(vec, vcpu->arch.apic);
+}
+EXPORT_SYMBOL_GPL(kvm_apic_clear_irr);
+
 static inline void apic_set_isr(int vec, struct kvm_lapic *apic)
 {
 	struct kvm_vcpu *vcpu;
@@ -2465,6 +2471,7 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
 	__apic_update_ppr(apic, &ppr);
 	return apic_has_interrupt_for_ppr(apic, ppr);
 }
+EXPORT_SYMBOL_GPL(kvm_apic_has_interrupt);
 
 int kvm_apic_accept_pic_intr(struct kvm_vcpu *vcpu)
 {

arch/x86/kvm/lapic.h

@@ -89,6 +89,7 @@ int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
 bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
 			   int shorthand, unsigned int dest, int dest_mode);
 int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2);
+void kvm_apic_clear_irr(struct kvm_vcpu *vcpu, int vec);
 bool __kvm_apic_update_irr(u32 *pir, void *regs, int *max_irr);
 bool kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir, int *max_irr);
 void kvm_apic_update_ppr(struct kvm_vcpu *vcpu);

arch/x86/kvm/vmx/nested.c

@@ -3531,6 +3531,14 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 	if (unlikely(status != NVMX_VMENTRY_SUCCESS))
 		goto vmentry_failed;
 
+	/* Emulate processing of posted interrupts on VM-Enter. */
+	if (nested_cpu_has_posted_intr(vmcs12) &&
+	    kvm_apic_has_interrupt(vcpu) == vmx->nested.posted_intr_nv) {
+		vmx->nested.pi_pending = true;
+		kvm_make_request(KVM_REQ_EVENT, vcpu);
+		kvm_apic_clear_irr(vcpu, vmx->nested.posted_intr_nv);
+	}
+
 	/* Hide L1D cache contents from the nested guest.  */
 	vmx->vcpu.arch.l1tf_flush_l1d = true;