This is a note to let you know that I've just added the patch titled
KVM: x86/pmu: Do not mask LVTPC when handling a PMI on AMD platforms
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-x86-pmu-do-not-mask-lvtpc-when-handling-a-pmi-on-amd-platforms.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 49ff3b4aec51e3abfc9369997cc603319b02af9a Mon Sep 17 00:00:00 2001
From: Sandipan Das <sandipan.das@xxxxxxx>
Date: Fri, 5 Apr 2024 16:55:55 -0700
Subject: KVM: x86/pmu: Do not mask LVTPC when handling a PMI on AMD platforms
From: Sandipan Das <sandipan.das@xxxxxxx>
commit 49ff3b4aec51e3abfc9369997cc603319b02af9a upstream.
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@xxxxxxxxxxxxxxx
Signed-off-by: Sandipan Das <sandipan.das@xxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
[sean: use is_intel_compatible instead of !is_amd_or_hygon()]
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-ID: <20240405235603.1173076-3-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/lapic.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2771,7 +2771,8 @@ int kvm_apic_local_deliver(struct kvm_la
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;
}
Patches currently in stable-queue which might be from sandipan.das@xxxxxxx are
queue-6.8/kvm-x86-pmu-do-not-mask-lvtpc-when-handling-a-pmi-on-amd-platforms.patch
