vmm: fix HLT loop while vcpu has requested virtual interrupts

This fixes the detection of pending interrupts when pirval is 0 and the
pending bit is set

More information how this situation occurs, can be found here:
https://github.com/freebsd/freebsd-src/blob/c5b5f2d8086f540fefe4826da013dd31d4e45fe8/sys/amd64/vmm/intel/vmx.c#L4016-L4031

Reviewed by:		corvink, markj
Fixes:			02cc877968bbcd57695035c67114a67427f54549 ("Recognize a pending virtual interrupt while emulating the halt instruction.")
MFC after:		1 week
Sponsored by:		vStack
Differential Revision:	https://reviews.freebsd.org/D39620

sys/amd64/vmm/intel/vmx.c

@@ -3763,7 +3763,8 @@ vmx_pending_intr(struct vlapic *vlapic, int *vecptr)
 	struct pir_desc *pir_desc;
 	struct LAPIC *lapic;
 	uint64_t pending, pirval;
-	uint32_t ppr, vpr;
+	uint8_t ppr, vpr, rvi;
+	struct vm_exit *vmexit;
 	int i;
 
 	/*
@@ -3774,31 +3775,26 @@ vmx_pending_intr(struct vlapic *vlapic, int *vecptr)
 
 	vlapic_vtx = (struct vlapic_vtx *)vlapic;
 	pir_desc = vlapic_vtx->pir_desc;
+	lapic = vlapic->apic_page;
 
-	pending = atomic_load_acq_long(&pir_desc->pending);
-	if (!pending) {
 	/*
 	 * While a virtual interrupt may have already been
 	 * processed the actual delivery maybe pending the
 	 * interruptibility of the guest.  Recognize a pending
 	 * interrupt by reevaluating virtual interrupts
-		 * following Section 29.2.1 in the Intel SDM Volume 3.
+	 * following Section 30.2.1 in the Intel SDM Volume 3.
 	 */
-		struct vm_exit *vmexit;
-		uint8_t rvi, ppr;
-
 	vmexit = vm_exitinfo(vlapic->vcpu);
 	KASSERT(vmexit->exitcode == VM_EXITCODE_HLT,
 	    ("vmx_pending_intr: exitcode not 'HLT'"));
 	rvi = vmexit->u.hlt.intr_status & APIC_TPR_INT;
-		lapic = vlapic->apic_page;
 	ppr = lapic->ppr & APIC_TPR_INT;
-		if (rvi > ppr) {
+	if (rvi > ppr)
 		return (1);
-		}
 
+	pending = atomic_load_acq_long(&pir_desc->pending);
+	if (!pending)
 		return (0);
-	}
 
 	/*
 	 * If there is an interrupt pending then it will be recognized only
@@ -3807,8 +3803,6 @@ vmx_pending_intr(struct vlapic *vlapic, int *vecptr)
 	 * Special case: if the processor priority is zero then any pending
 	 * interrupt will be recognized.
 	 */
-	lapic = vlapic->apic_page;
-	ppr = lapic->ppr & APIC_TPR_INT;
 	if (ppr == 0)
 		return (1);