Patch-mainline: v6.6-rc7
Git-commit: a16eb25b09c02a54c1c1b449d4b6cfa2cf3f013a
References: jsc#PED-7322
From: Jim Mattson <jmattson@google.com>
Date: Mon, 25 Sep 2023 17:34:47 +0000
Subject: [PATCH] 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: f5132b01386b ("KVM: Expose a version 2 architectural PMU to a guests")
Cc: stable@vger.kernel.org
Signed-off-by: Jim Mattson <jmattson@google.com>
Tested-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20230925173448.3518223-3-mizhang@google.com
[sean: massage changelog, correct Fixes]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/kvm/lapic.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index dcd60b39e794..3e977dbbf993 100644
--- a/arch/x86/kvm/lapic.c
+++ b/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;
 }
-- 
2.35.3