[PATCH 2/2] KVM: x86: Mask LVTPC when handling a PMI

From: Jim Mattson <jmattson@google.com>
To: kvm@vger.kernel.org, Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: Like Xu <likexu@tencent.com>, Mingwei Zhang <mizhang@google.com>,
	Roman Kagan <rkagan@amazon.de>, Kan Liang <kan.liang@intel.com>,
	Dapeng1 Mi <dapeng1.mi@intel.com>,
	Jim Mattson <jmattson@google.com>
Subject: [PATCH 2/2] KVM: x86: Mask LVTPC when handling a PMI
Date: Fri,  1 Sep 2023 11:56:46 -0700	[thread overview]
Message-ID: <20230901185646.2823254-2-jmattson@google.com> (raw)
In-Reply-To: <20230901185646.2823254-1-jmattson@google.com>

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, to reduce the
incidence of "dazed and confused" spurious NMI warnings in Linux
guests (at least, those that use a PMI handler with "late_ack").

Fixes: 23930f9521c9 ("KVM: x86: Enable NMI Watchdog via in-kernel PIT source")
Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/kvm/lapic.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index a983a16163b1..1a79ec54ae1e 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2743,6 +2743,8 @@ int kvm_apic_local_deliver(struct kvm_lapic *apic, int lvt_type)
 		vector = reg & APIC_VECTOR_MASK;
 		mode = reg & APIC_MODE_MASK;
 		trig_mode = reg & APIC_LVT_LEVEL_TRIGGER;
+		if (lvt_type == APIC_LVTPC)
+			kvm_lapic_set_reg(apic, lvt_type, reg | APIC_LVT_MASKED);
 		return __apic_accept_irq(apic, mode, vector, 1, trig_mode,
 					NULL);
 	}
-- 
2.42.0.283.g2d96d420d3-goog

