Re: [PATCH 5.4] KVM: x86/svm: Account for family 17h event renumberings in amd_pmc_perf_hw_id

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On 5/8/22 18:54, Kyle Huey wrote:
From: Kyle Huey <me@xxxxxxxxxxxx>

commit 5eb849322d7f7ae9d5c587c7bc3b4f7c6872cd2f upstream

Zen renumbered some of the performance counters that correspond to the
well known events in perf_hw_id. This code in KVM was never updated for
that, so guest that attempt to use counters on Zen that correspond to the
pre-Zen perf_hw_id values will silently receive the wrong values.

This has been observed in the wild with rr[0] when running in Zen 3
guests. rr uses the retired conditional branch counter 00d1 which is
incorrectly recognized by KVM as PERF_COUNT_HW_STALLED_CYCLES_BACKEND.

[0] https://rr-project.org/

Signed-off-by: Kyle Huey <me@xxxxxxxxxxxx>
Message-Id: <20220503050136.86298-1-khuey@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
[Check guest family, not host. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
[Backport to 5.4: adjusted context]
Signed-off-by: Kyle Huey <me@xxxxxxxxxxxx>
---
  arch/x86/kvm/pmu_amd.c | 28 +++++++++++++++++++++++++---
  1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/pmu_amd.c b/arch/x86/kvm/pmu_amd.c
index 6bc656abbe66..3ccfd1abcbad 100644
--- a/arch/x86/kvm/pmu_amd.c
+++ b/arch/x86/kvm/pmu_amd.c
@@ -44,6 +44,22 @@ static struct kvm_event_hw_type_mapping amd_event_mapping[] = {
  	[7] = { 0xd1, 0x00, PERF_COUNT_HW_STALLED_CYCLES_BACKEND },
  };
+/* duplicated from amd_f17h_perfmon_event_map. */
+static struct kvm_event_hw_type_mapping amd_f17h_event_mapping[] = {
+	[0] = { 0x76, 0x00, PERF_COUNT_HW_CPU_CYCLES },
+	[1] = { 0xc0, 0x00, PERF_COUNT_HW_INSTRUCTIONS },
+	[2] = { 0x60, 0xff, PERF_COUNT_HW_CACHE_REFERENCES },
+	[3] = { 0x64, 0x09, PERF_COUNT_HW_CACHE_MISSES },
+	[4] = { 0xc2, 0x00, PERF_COUNT_HW_BRANCH_INSTRUCTIONS },
+	[5] = { 0xc3, 0x00, PERF_COUNT_HW_BRANCH_MISSES },
+	[6] = { 0x87, 0x02, PERF_COUNT_HW_STALLED_CYCLES_FRONTEND },
+	[7] = { 0x87, 0x01, PERF_COUNT_HW_STALLED_CYCLES_BACKEND },
+};
+
+/* amd_pmc_perf_hw_id depends on these being the same size */
+static_assert(ARRAY_SIZE(amd_event_mapping) ==
+	     ARRAY_SIZE(amd_f17h_event_mapping));
+
  static unsigned int get_msr_base(struct kvm_pmu *pmu, enum pmu_type type)
  {
  	struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
@@ -130,17 +146,23 @@ static unsigned amd_find_arch_event(struct kvm_pmu *pmu,
  				    u8 event_select,
  				    u8 unit_mask)
  {
+	struct kvm_event_hw_type_mapping *event_mapping;
  	int i;
+ if (guest_cpuid_family(pmc->vcpu) >= 0x17)
+		event_mapping = amd_f17h_event_mapping;
+	else
+		event_mapping = amd_event_mapping;
+
  	for (i = 0; i < ARRAY_SIZE(amd_event_mapping); i++)
-		if (amd_event_mapping[i].eventsel == event_select
-		    && amd_event_mapping[i].unit_mask == unit_mask)
+		if (event_mapping[i].eventsel == event_select
+		    && event_mapping[i].unit_mask == unit_mask)
  			break;
if (i == ARRAY_SIZE(amd_event_mapping))
  		return PERF_COUNT_HW_MAX;
- return amd_event_mapping[i].event_type;
+	return event_mapping[i].event_type;
  }
/* return PERF_COUNT_HW_MAX as AMD doesn't have fixed events */

Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

Thanks,

Paolo




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