As the branches event overcount issue on Atom platforms, once there are
VM-Exits triggered (external interrupts) in the guest loop, the measured
branch event count could be larger than NUM_BRANCHES, this would lead to
the pmu_event_filter_test print warning to info the measured branches
event count is mismatched with expected number (NUM_BRANCHES).

To eliminate this warning, relax the branches event count check on the
Atom platform which have the branches event overcount issue.

Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Yi Lai <yi1.lai@intel.com>
---
 tools/testing/selftests/kvm/x86/pmu_event_filter_test.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c b/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
index c15513cd74d1..9c1a92f05786 100644
--- a/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
+++ b/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
@@ -60,6 +60,8 @@ struct {
 	uint64_t instructions_retired;
 } pmc_results;
 
+static uint8_t inst_overcount_flags;
+
 /*
  * If we encounter a #GP during the guest PMU sanity check, then the guest
  * PMU is not functional. Inform the hypervisor via GUEST_SYNC(0).
@@ -214,8 +216,10 @@ static void remove_event(struct __kvm_pmu_event_filter *f, uint64_t event)
 do {											\
 	uint64_t br = pmc_results.branches_retired;					\
 	uint64_t ir = pmc_results.instructions_retired;					\
+	bool br_matched = inst_overcount_flags & BR_RETIRED_OVERCOUNT ?			\
+			  br >= NUM_BRANCHES : br == NUM_BRANCHES;			\
 											\
-	if (br && br != NUM_BRANCHES)							\
+	if (br && !br_matched)								\
 		pr_info("%s: Branch instructions retired = %lu (expected %u)\n",	\
 			__func__, br, NUM_BRANCHES);					\
 	TEST_ASSERT(br, "%s: Branch instructions retired = %lu (expected > 0)",		\
@@ -850,6 +854,9 @@ int main(int argc, char *argv[])
 	if (use_amd_pmu())
 		test_amd_deny_list(vcpu);
 
+	if (use_intel_pmu())
+		inst_overcount_flags = detect_inst_overcount_flags();
+
 	test_without_filter(vcpu);
 	test_member_deny_list(vcpu);
 	test_member_allow_list(vcpu);
-- 
2.34.1

On Fri, Jul 18, 2025, Dapeng Mi wrote:
> As the branches event overcount issue on Atom platforms, once there are
> VM-Exits triggered (external interrupts) in the guest loop, the measured
> branch event count could be larger than NUM_BRANCHES, this would lead to
> the pmu_event_filter_test print warning to info the measured branches
> event count is mismatched with expected number (NUM_BRANCHES).
> 
> To eliminate this warning, relax the branches event count check on the
> Atom platform which have the branches event overcount issue.
> 
> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> Tested-by: Yi Lai <yi1.lai@intel.com>
> ---

This can be squashed with the previous patch, "workaround errata" is a single
logical change as far as I'm concerned.

>  tools/testing/selftests/kvm/x86/pmu_event_filter_test.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c b/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
> index c15513cd74d1..9c1a92f05786 100644
> --- a/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
> +++ b/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
> @@ -60,6 +60,8 @@ struct {
>  	uint64_t instructions_retired;
>  } pmc_results;
>  
> +static uint8_t inst_overcount_flags;
> +
>  /*
>   * If we encounter a #GP during the guest PMU sanity check, then the guest
>   * PMU is not functional. Inform the hypervisor via GUEST_SYNC(0).
> @@ -214,8 +216,10 @@ static void remove_event(struct __kvm_pmu_event_filter *f, uint64_t event)
>  do {											\
>  	uint64_t br = pmc_results.branches_retired;					\
>  	uint64_t ir = pmc_results.instructions_retired;					\
> +	bool br_matched = inst_overcount_flags & BR_RETIRED_OVERCOUNT ?			\
> +			  br >= NUM_BRANCHES : br == NUM_BRANCHES;			\
>  											\
> -	if (br && br != NUM_BRANCHES)							\
> +	if (br && !br_matched)								\
>  		pr_info("%s: Branch instructions retired = %lu (expected %u)\n",	\
>  			__func__, br, NUM_BRANCHES);					\
>  	TEST_ASSERT(br, "%s: Branch instructions retired = %lu (expected > 0)",		\
> @@ -850,6 +854,9 @@ int main(int argc, char *argv[])
>  	if (use_amd_pmu())
>  		test_amd_deny_list(vcpu);
>  
> +	if (use_intel_pmu())

Checking for an Intel CPU should be done by the library.