KVM: selftests: Handle Intel Atom errata that leads to PMU event overcount

Add a PMU errata framework and use it to relax precise event counts on
Atom platforms that overcount "Instruction Retired" and "Branch Instruction
Retired" events, as the overcount issues on VM-Exit/VM-Entry are impossible
to prevent from userspace, e.g. the test can't prevent host IRQs.

Setup errata during early initialization and automatically sync the mask
to VMs so that tests can check for errata without having to manually
manage host=>guest variables.

For Intel Atom CPUs, the PMU events "Instruction Retired" or
"Branch Instruction Retired" may be overcounted for some certain
instructions, like FAR CALL/JMP, RETF, IRET, VMENTRY/VMEXIT/VMPTRLD
and complex SGX/SMX/CSTATE instructions/flows.

The detailed information can be found in the errata (section SRF7):
https://edc.intel.com/content/www/us/en/design/products-and-solutions/processors-and-chipsets/sierra-forest/xeon-6700-series-processor-with-e-cores-specification-update/errata-details/

For the Atom platforms before Sierra Forest (including Sierra Forest),
Both 2 events "Instruction Retired" and "Branch Instruction Retired" would
be overcounted on these certain instructions, but for Clearwater Forest
only "Instruction Retired" event is overcounted on these instructions.

Signed-off-by: dongsheng <dongsheng.x.zhang@intel.com>
Co-developed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Yi Lai <yi1.lai@intel.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20250919214648.1585683-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

2 files changed, 48 insertions, 0 deletions

diff --git a/tools/testing/selftests/kvm/lib/x86/pmu.c b/tools/testing/selftests/kvm/lib/x86/pmu.c
index 5ab44bf54773..34cb57d1d671 100644
--- a/tools/testing/selftests/kvm/lib/x86/pmu.c
+++ b/tools/testing/selftests/kvm/lib/x86/pmu.c
@@ -8,6 +8,7 @@
 #include <linux/kernel.h>
 
 #include "kvm_util.h"
+#include "processor.h"
 #include "pmu.h"
 
 const uint64_t intel_pmu_arch_events[] = {
@@ -34,3 +35,46 @@ const uint64_t amd_pmu_zen_events[] = {
 	AMD_ZEN_BRANCHES_MISPREDICTED,
 };
 kvm_static_assert(ARRAY_SIZE(amd_pmu_zen_events) == NR_AMD_ZEN_EVENTS);
+
+/*
+ * For Intel Atom CPUs, the PMU events "Instruction Retired" or
+ * "Branch Instruction Retired" may be overcounted for some certain
+ * instructions, like FAR CALL/JMP, RETF, IRET, VMENTRY/VMEXIT/VMPTRLD
+ * and complex SGX/SMX/CSTATE instructions/flows.
+ *
+ * The detailed information can be found in the errata (section SRF7):
+ * https://edc.intel.com/content/www/us/en/design/products-and-solutions/processors-and-chipsets/sierra-forest/xeon-6700-series-processor-with-e-cores-specification-update/errata-details/
+ *
+ * For the Atom platforms before Sierra Forest (including Sierra Forest),
+ * Both 2 events "Instruction Retired" and "Branch Instruction Retired" would
+ * be overcounted on these certain instructions, but for Clearwater Forest
+ * only "Instruction Retired" event is overcounted on these instructions.
+ */
+static uint64_t get_pmu_errata(void)
+{
+	if (!this_cpu_is_intel())
+		return 0;
+
+	if (this_cpu_family() != 0x6)
+		return 0;
+
+	switch (this_cpu_model()) {
+	case 0xDD: /* Clearwater Forest */
+		return BIT_ULL(INSTRUCTIONS_RETIRED_OVERCOUNT);
+	case 0xAF: /* Sierra Forest */
+	case 0x4D: /* Avaton, Rangely */
+	case 0x5F: /* Denverton */
+	case 0x86: /* Jacobsville */
+		return BIT_ULL(INSTRUCTIONS_RETIRED_OVERCOUNT) |
+		       BIT_ULL(BRANCHES_RETIRED_OVERCOUNT);
+	default:
+		return 0;
+	}
+}
+
+uint64_t pmu_errata_mask;
+
+void kvm_init_pmu_errata(void)
+{
+	pmu_errata_mask = get_pmu_errata();
+}
diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
index 3b63c99f7b96..4402d2e1ea69 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -6,6 +6,7 @@
 #include "linux/bitmap.h"
 #include "test_util.h"
 #include "kvm_util.h"
+#include "pmu.h"
 #include "processor.h"
 #include "sev.h"
 
@@ -638,6 +639,7 @@ void kvm_arch_vm_post_create(struct kvm_vm *vm)
 	sync_global_to_guest(vm, host_cpu_is_intel);
 	sync_global_to_guest(vm, host_cpu_is_amd);
 	sync_global_to_guest(vm, is_forced_emulation_enabled);
+	sync_global_to_guest(vm, pmu_errata_mask);
 
 	if (is_sev_vm(vm)) {
 		struct kvm_sev_init init = { 0 };
@@ -1269,6 +1271,8 @@ void kvm_selftest_arch_init(void)
 	host_cpu_is_intel = this_cpu_is_intel();
 	host_cpu_is_amd = this_cpu_is_amd();
 	is_forced_emulation_enabled = kvm_is_forced_emulation_enabled();
+
+	kvm_init_pmu_errata();
 }
 
 bool sys_clocksource_is_based_on_tsc(void)