kvm: nVMX: fix entry with pending interrupt if APICv is enabled

Commit b5861e5cf2fcf83031ea3e26b0a69d887adf7d21 introduced a check on
the interrupt-window and NMI-window CPU execution controls in order to
inject an external interrupt vmexit before the first guest instruction
executes. However, when APIC virtualization is enabled the host does not
need a vmexit in order to inject an interrupt at the next interrupt window;
instead, it just places the interrupt vector in RVI and the processor will
inject it as soon as possible. Therefore, on machines with APICv it is
not enough to check the CPU execution controls: the same scenario can also
happen if RVI>vPPR.

Fixes: b5861e5cf2fcf83031ea3e26b0a69d887adf7d21
Reviewed-by: Nikita Leshchenko <[e-mail]>
Cc: Sean Christopherson <[e-mail]>
Cc: Liran Alon <[e-mail]>
Cc: Radim Krčmář <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/kvm/vmx.c

···
 	nested_mark_vmcs12_pages_dirty(vcpu);
 }
 
+static u8 vmx_get_rvi(void)
+{
+	return vmcs_read16(GUEST_INTR_STATUS) & 0xff;
+}
+
 static bool vmx_guest_apic_has_interrupt(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
···
 		WARN_ON_ONCE(!vmx->nested.virtual_apic_page))
 		return false;
 
-	rvi = vmcs_read16(GUEST_INTR_STATUS) & 0xff;
+	rvi = vmx_get_rvi();
 
 	vapic_page = kmap(vmx->nested.virtual_apic_page);
 	vppr = *((u32 *)(vapic_page + APIC_PROCPRI));
···
 	return max_irr;
 }
 
+static u8 vmx_has_apicv_interrupt(struct kvm_vcpu *vcpu)
+{
+	u8 rvi = vmx_get_rvi();
+	u8 vppr = kvm_lapic_get_reg(vcpu->arch.apic, APIC_PROCPRI);
+
+	return ((rvi & 0xf0) > (vppr & 0xf0));
+}
+
 static void vmx_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
 {
 	if (!kvm_vcpu_apicv_active(vcpu))
···
 	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
 	bool from_vmentry = !!exit_qual;
 	u32 dummy_exit_qual;
-	u32 vmcs01_cpu_exec_ctrl;
+	bool evaluate_pending_interrupts;
 	int r = 0;
 
-	vmcs01_cpu_exec_ctrl = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL);
+	evaluate_pending_interrupts = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL) &
+		(CPU_BASED_VIRTUAL_INTR_PENDING | CPU_BASED_VIRTUAL_NMI_PENDING);
+	if (likely(!evaluate_pending_interrupts) && kvm_vcpu_apicv_active(vcpu))
+		evaluate_pending_interrupts |= vmx_has_apicv_interrupt(vcpu);
 
 	enter_guest_mode(vcpu);
 
···
 	 * to L1 or delivered directly to L2 (e.g. In case L1 don't
 	 * intercept EXTERNAL_INTERRUPT).
 	 *
-	 * Usually this would be handled by L0 requesting a
-	 * IRQ/NMI window by setting VMCS accordingly. However,
-	 * this setting was done on VMCS01 and now VMCS02 is active
-	 * instead. Thus, we force L0 to perform pending event
-	 * evaluation by requesting a KVM_REQ_EVENT.
+	 * Usually this would be handled by the processor noticing an
+	 * IRQ/NMI window request, or checking RVI during evaluation of
+	 * pending virtual interrupts.  However, this setting was done
+	 * on VMCS01 and now VMCS02 is active instead. Thus, we force L0
+	 * to perform pending event evaluation by requesting a KVM_REQ_EVENT.
 	 */
-	if (vmcs01_cpu_exec_ctrl &
-		(CPU_BASED_VIRTUAL_INTR_PENDING | CPU_BASED_VIRTUAL_NMI_PENDING)) {
+	if (unlikely(evaluate_pending_interrupts))
 		kvm_make_request(KVM_REQ_EVENT, vcpu);
-	}
 
 	/*
 	 * Note no nested_vmx_succeed or nested_vmx_fail here. At this point