KVM: x86/pmu: Do not mask LVTPC when handling a PMI on AMD platforms

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>