[PATCH v4 21/21] KVM: selftests: Support fixed counters bitmap in pmu_counters_test

[Zide Chen <zide.chen@intel.com>]

From: Dapeng Mi <dapeng1.mi@linux.intel.com>

On PerfMon v5, CPUID.0AH:ECX represents the fixed counter bitmask,
while EDX[4:0] indicates the number of contiguous fixed counters
starting from 0:

FxCtr[i]_is_supported := ECX[i] || (EDX[4:0] > i).

Fix test_fixed_counters() to derive supported fixed counters using the
above formula instead of relying solely on EDX[4:0]. This allows the
test to cover non-contiguous fixed counter configurations.

Update this_pmu_has() to take the PMU version into consideration.
Without this fix, it could return incorrect results in test cases such
as test_arch_events(), which configure a PMU version different from
the one originally advertised by KVM without explicitly updating
CPUID.0AH:{ECX,EDX} to match the new PMU version.

For example, after downgrading a guest from PMU v5 to PMU v2,
this_pmu_has() would still consult CPUID.0AH:ECX while KVM ignores it,
resulting in a mismatch in the reported fixed counter capabilities.

Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Co-developed-by: Zide Chen <zide.chen@intel.com>
Signed-off-by: Zide Chen <zide.chen@intel.com>
---
v3:
- use the BIT() macro instead of an open-coded left shift. (Sashiko)
- Simplified ternary condition in this_pmu_has(). (Sashiko)
- Also test legacy EDX contiguous counts with ECX=0 in
  test_fixed_counters(). (Sashiko)

v2:
- Fix this_pmu_has() to honor the guest's configured PMU version.
- Update the pmu_vm_create_with_vcpus() calls after rebasing.
---
 .../selftests/kvm/include/x86/processor.h     |  6 +++-
 .../selftests/kvm/x86/pmu_counters_test.c     | 29 +++++++++++++++----
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index ffec2291b1e1..21381db1c4ca 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -836,6 +836,7 @@ static __always_inline bool this_cpu_has_p(struct kvm_x86_cpu_property property)
 
 static inline bool this_pmu_has(struct kvm_x86_pmu_feature feature)
 {
+	u8 pmu_version;
 	u32 nr_bits;
 
 	if (feature.f.reg == KVM_CPUID_EBX) {
@@ -845,7 +846,10 @@ static inline bool this_pmu_has(struct kvm_x86_pmu_feature feature)
 
 	GUEST_ASSERT(feature.f.reg == KVM_CPUID_ECX);
 	nr_bits = this_cpu_property(X86_PROPERTY_PMU_NR_FIXED_COUNTERS);
-	return nr_bits > feature.f.bit || this_cpu_has(feature.f);
+	pmu_version = this_cpu_property(X86_PROPERTY_PMU_VERSION);
+
+	return nr_bits > feature.f.bit ||
+	       (pmu_version >= 5 && this_cpu_has(feature.f));
 }
 
 static __always_inline u64 this_cpu_supported_xcr0(void)
diff --git a/tools/testing/selftests/kvm/x86/pmu_counters_test.c b/tools/testing/selftests/kvm/x86/pmu_counters_test.c
index c3e784e16348..61e6fe5b6ef4 100644
--- a/tools/testing/selftests/kvm/x86/pmu_counters_test.c
+++ b/tools/testing/selftests/kvm/x86/pmu_counters_test.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2023, Tencent, Inc.
  */
 #include <x86intrin.h>
+#include <linux/bitmap.h>
 
 #include "pmu.h"
 #include "processor.h"
@@ -631,25 +632,43 @@ static void __test_fixed_counters(struct kvm_vcpu *vcpu, u8 nr_fixed_counters,
 static void test_fixed_counters(u8 pmu_version, u64 perf_capabilities)
 {
 	u8 nr_fixed_counters = kvm_cpu_property(X86_PROPERTY_PMU_NR_FIXED_COUNTERS);
+	unsigned long fixed_subset;
 	struct kvm_vcpu **vcpus;
 	struct kvm_vm *vm;
+	u32 fixed_bitmap;
 	int i = 0;
-	u32 k;
 	u8 j;
 
 	pr_info("Testing %u fixed counters, PMU version %u, perf_caps = %lx\n",
 		nr_fixed_counters, pmu_version, perf_capabilities);
 
+	fixed_bitmap = BIT(nr_fixed_counters) - 1;
+	if (pmu_version >= 5)
+		fixed_bitmap |= kvm_cpu_property(X86_PROPERTY_PMU_FIXED_COUNTERS_BITMASK);
 
-	vm = pmu_vm_create_with_vcpus((nr_fixed_counters + 1) * BIT(nr_fixed_counters),
+	/* One vCPU per subset of fixed_bitmap, plus one per legacy EDX test. */
+	vm = pmu_vm_create_with_vcpus(BIT(__builtin_popcount(fixed_bitmap)) + nr_fixed_counters,
 				      guest_test_fixed_counters,
 				      pmu_version, perf_capabilities, &vcpus);
 
-	for (j = 0; j <= nr_fixed_counters; j++) {
-		for (k = 0; k <= (BIT(nr_fixed_counters) - 1); k++)
-			__test_fixed_counters(vcpus[i++], j, k);
+	for (fixed_subset = 0; fixed_subset <= fixed_bitmap; fixed_subset++) {
+		u32 nr_contiguous;
+
+		/*
+		 * The loop walks all values from 0 to fixed_bitmap, so skip any
+		 * value that is not a subset of fixed_bitmap.
+		 */
+		if (fixed_subset & ~fixed_bitmap)
+			continue;
+
+		nr_contiguous = find_first_zero_bit(&fixed_subset,
+						    MAX_NR_FIXED_COUNTERS);
+		__test_fixed_counters(vcpus[i++], nr_contiguous, fixed_subset);
 	}
 
+	for (j = 1; j <= nr_fixed_counters; j++)
+		__test_fixed_counters(vcpus[i++], j, 0);
+
 	pmu_vm_free(vm, vcpus);
 }
 
-- 
2.56.1