[PATCH v2 03/54] KVM: x86/pmu: Do not mask LVTPC when handling a PMI on AMD platforms

Mingwei Zhang
2024-05-06T05:30:33Z

From: Sandipan Das <sandipan.das@amd.com>

On AMD and Hygon platforms, the local APIC does not automatically set
the mask bit of the LVTPC register when handling a PMI and there is
no need to clear it in the kernel's PMI handler.

For guests, the mask bit is currently set by kvm_apic_local_deliver()
and unless it is cleared by the guest kernel's PMI handler, PMIs stop
arriving and break use-cases like sampling with perf record.

This does not affect non-PerfMonV2 guests because PMIs are handled in
the guest kernel by x86_pmu_handle_irq() which always clears the LVTPC
mask bit irrespective of the vendor.

Before:

$ perf record -e cycles:u true
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.001 MB perf.data (1 samples) ]

After:

$ perf record -e cycles:u true
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.002 MB perf.data (19 samples) ]

Fixes: a16eb25b09c0 ("KVM: x86: Mask LVTPC when handling a PMI")
Cc: stable@vger.kernel.org
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
[sean: use is_intel_compatible instead of !is_amd_or_hygon()]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240405235603.1173076-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/lapic.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index cf37586f0466..ebf41023be38 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2776,7 +2776,8 @@ int kvm_apic_local_deliver(struct kvm_lapic *apic, int lvt_type)
trig_mode = reg & APIC_LVT_LEVEL_TRIGGER;

r = __apic_accept_irq(apic, mode, vector, 1, trig_mode, NULL);
- if (r && lvt_type == APIC_LVTPC)
+ if (r && lvt_type == APIC_LVTPC &&
+ guest_cpuid_is_intel_compatible(apic->vcpu))
kvm_lapic_set_reg(apic, APIC_LVTPC, reg | APIC_LVT_MASKED);
return r;
}
--
2.45.0.rc1.225.g2a3ae87e7f-goog