KVM: x86: Mask LVTPC when handling a PMI

Per the SDM, "When the local APIC handles a performance-monitoring
counters interrupt, it automatically sets the mask flag in the LVT
performance counter register."  Add this behavior to KVM's local APIC
emulation.

Failure to mask the LVTPC entry results in spurious PMIs, e.g. when
running Linux as a guest, PMI handlers that do a "late_ack" spew a large
number of "dazed and confused" spurious NMI warnings.

Fixes: f5132b0 ("KVM: Expose a version 2 architectural PMU to a guests")
Cc: [email protected]
Signed-off-by: Jim Mattson <[email protected]>
Tested-by: Mingwei Zhang <[email protected]>
Signed-off-by: Mingwei Zhang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[sean: massage changelog, correct Fixes]
Signed-off-by: Sean Christopherson <[email protected]>

Author: jsmattsonjr

arch/x86/kvm/lapic.c

@@ -2759,13 +2759,17 @@ int kvm_apic_local_deliver(struct kvm_lapic *apic, int lvt_type)
 {
 	u32 reg = kvm_lapic_get_reg(apic, lvt_type);
 	int vector, mode, trig_mode;
+	int r;
 
 	if (kvm_apic_hw_enabled(apic) && !(reg & APIC_LVT_MASKED)) {
 		vector = reg & APIC_VECTOR_MASK;
 		mode = reg & APIC_MODE_MASK;
 		trig_mode = reg & APIC_LVT_LEVEL_TRIGGER;
-		return __apic_accept_irq(apic, mode, vector, 1, trig_mode,
-					NULL);
+
+		r = __apic_accept_irq(apic, mode, vector, 1, trig_mode, NULL);
+		if (r && lvt_type == APIC_LVTPC)
+			kvm_lapic_set_reg(apic, APIC_LVTPC, reg | APIC_LVT_MASKED);
+		return r;
 	}
 	return 0;
 }