The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y git checkout FETCH_HEAD git cherry-pick -x 49ff3b4aec51e3abfc9369997cc603319b02af9a # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024042325-rockstar-civic-9c1a@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

49ff3b4aec51 ("KVM: x86/pmu: Do not mask LVTPC when handling a PMI on AMD platforms") a16eb25b09c0 ("KVM: x86: Mask LVTPC when handling a PMI")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 49ff3b4aec51e3abfc9369997cc603319b02af9a Mon Sep 17 00:00:00 2001 From: Sandipan Das sandipan.das@amd.com Date: Fri, 5 Apr 2024 16:55:55 -0700 Subject: [PATCH] KVM: x86/pmu: Do not mask LVTPC when handling a PMI on AMD platforms

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

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; }