[PATCH v3 08/18] KVM: x86/pmu: Switch to bitmask-based KVM PMU capabilities
From: Zide Chen
Date: Thu Nov 05 2026 - 20:52:18 EST
From: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Intel platforms support non-contiguous fixed counters via CPUID.0AH:ECX
starting with PerfMon v5, and support non-contiguous GP counters
through the Architectural PerfMon Extension (CPUID leaf 23H).
struct x86_pmu_capability now exposes {,fixed_}cntr_mask64 bitmaps,
which may contain sparse bits representing non-contiguous counters.
Switch KVM's kvm_host_pmu and kvm_pmu_cap consumers over to the new
bitmask fields, including iterating kvm_host_pmu bitmasks directly in
VMX and SVM PMU MSR intercept setup.
CPUID.0AH:EAX[15:8] and CPUID.0AH:EDX[4:0] enumerate only contiguous
counters. Derive these values from kvm_pmu_cap.{,fixed_}cntr_mask64 as
the number of consecutive counters starting at index 0.
Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Co-developed-by: Zide Chen <zide.chen@xxxxxxxxx>
Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
Reviewed-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
---
v3:
- Iterate kvm_host_pmu bitmasks directly in VMX and SVM intercept loops.
- Clamp nr_{gp,fixed}_counters to the number of contiguous counters
supported by KVM in intel_pmu_refresh(). (Jim, Sashiko)
- Drop redundant !enable_mediated_pmu clamp on fixed_cntr_mask64. (Sashiko)
---
arch/x86/kvm/cpuid.c | 14 +++++++++++---
arch/x86/kvm/msrs.c | 12 ++++++------
arch/x86/kvm/pmu.c | 17 ++++++++---------
arch/x86/kvm/svm/pmu.c | 2 +-
arch/x86/kvm/svm/svm.c | 7 +++----
arch/x86/kvm/vmx/pmu_intel.c | 28 +++++++++++++++++++---------
arch/x86/kvm/vmx/vmx.c | 4 ++--
7 files changed, 50 insertions(+), 34 deletions(-)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index adafd6fa2c54..3310c370c5fa 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1535,10 +1535,18 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
}
eax.split.version_id = kvm_pmu_cap.version;
- eax.split.num_counters = kvm_pmu_cap.num_counters_gp;
+
+ /* Contiguous GP counters only. */
+ eax.split.num_counters =
+ find_first_zero_bit(kvm_pmu_cap.cntr_mask,
+ KVM_MAX_NR_GP_COUNTERS);
eax.split.bit_width = kvm_pmu_cap.bit_width_gp;
eax.split.mask_length = kvm_pmu_cap.events_mask_len;
- edx.split.num_counters_fixed = kvm_pmu_cap.num_counters_fixed;
+
+ /* Contiguous fixed counters only. */
+ edx.split.num_counters_fixed =
+ find_first_zero_bit(kvm_pmu_cap.fixed_cntr_mask,
+ KVM_MAX_NR_FIXED_COUNTERS);
edx.split.bit_width_fixed = kvm_pmu_cap.bit_width_fixed;
if (kvm_pmu_cap.version)
@@ -1903,7 +1911,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
cpuid_entry_override(entry, CPUID_8000_0022_EAX);
- ebx.split.num_core_pmc = kvm_pmu_cap.num_counters_gp;
+ ebx.split.num_core_pmc = hweight64(kvm_pmu_cap.cntr_mask64);
entry->ebx = ebx.full;
break;
}
diff --git a/arch/x86/kvm/msrs.c b/arch/x86/kvm/msrs.c
index e91650af44c2..01fb130a7d24 100644
--- a/arch/x86/kvm/msrs.c
+++ b/arch/x86/kvm/msrs.c
@@ -2621,20 +2621,20 @@ static void kvm_probe_msr_to_save(u32 msr_index)
break;
case MSR_ARCH_PERFMON_PERFCTR0 ...
MSR_ARCH_PERFMON_PERFCTR0 + KVM_MAX_NR_GP_COUNTERS - 1:
- if (msr_index - MSR_ARCH_PERFMON_PERFCTR0 >=
- kvm_pmu_cap.num_counters_gp)
+ if (!(BIT_ULL(msr_index - MSR_ARCH_PERFMON_PERFCTR0) &
+ kvm_pmu_cap.cntr_mask64))
return;
break;
case MSR_ARCH_PERFMON_EVENTSEL0 ...
MSR_ARCH_PERFMON_EVENTSEL0 + KVM_MAX_NR_GP_COUNTERS - 1:
- if (msr_index - MSR_ARCH_PERFMON_EVENTSEL0 >=
- kvm_pmu_cap.num_counters_gp)
+ if (!(BIT_ULL(msr_index - MSR_ARCH_PERFMON_EVENTSEL0) &
+ kvm_pmu_cap.cntr_mask64))
return;
break;
case MSR_ARCH_PERFMON_FIXED_CTR0 ...
MSR_ARCH_PERFMON_FIXED_CTR0 + KVM_MAX_NR_FIXED_COUNTERS - 1:
- if (msr_index - MSR_ARCH_PERFMON_FIXED_CTR0 >=
- kvm_pmu_cap.num_counters_fixed)
+ if (!(BIT_ULL(msr_index - MSR_ARCH_PERFMON_FIXED_CTR0) &
+ kvm_pmu_cap.fixed_cntr_mask64))
return;
break;
case MSR_AMD64_PERF_CNTR_GLOBAL_CTL:
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index b9c493c6db48..27d6a9169821 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -20,7 +20,6 @@
#include <asm/perf_event.h>
#include <asm/cpu_device_id.h>
#include "x86.h"
-#include "cpuid.h"
#include "lapic.h"
#include "pmu.h"
@@ -156,8 +155,8 @@ void kvm_init_pmu_capability(struct kvm_pmu_ops *pmu_ops)
* there are a non-zero number of counters, but fewer than what
* is architecturally required.
*/
- if (!kvm_host_pmu.num_counters_gp ||
- WARN_ON_ONCE(kvm_host_pmu.num_counters_gp < min_nr_gp_ctrs))
+ if (!kvm_host_pmu.cntr_mask64 ||
+ WARN_ON_ONCE(hweight64(kvm_host_pmu.cntr_mask64) < min_nr_gp_ctrs))
enable_pmu = false;
else if (is_intel && !kvm_host_pmu.version)
enable_pmu = false;
@@ -177,10 +176,10 @@ void kvm_init_pmu_capability(struct kvm_pmu_ops *pmu_ops)
memcpy(&kvm_pmu_cap, &kvm_host_pmu, sizeof(kvm_host_pmu));
kvm_pmu_cap.version = min(kvm_pmu_cap.version, 2);
- kvm_pmu_cap.num_counters_gp = min(kvm_pmu_cap.num_counters_gp,
- pmu_ops->MAX_NR_GP_COUNTERS);
- kvm_pmu_cap.num_counters_fixed = min(kvm_pmu_cap.num_counters_fixed,
- KVM_MAX_NR_FIXED_COUNTERS);
+ kvm_pmu_cap.cntr_mask64 &=
+ GENMASK_ULL(pmu_ops->MAX_NR_GP_COUNTERS - 1, 0);
+ kvm_pmu_cap.fixed_cntr_mask64 &=
+ GENMASK_ULL(KVM_MAX_NR_FIXED_COUNTERS - 1, 0);
kvm_pmu_eventsel.INSTRUCTIONS_RETIRED =
perf_get_hw_event_config(PERF_COUNT_HW_INSTRUCTIONS);
@@ -788,8 +787,8 @@ static bool kvm_need_any_pmc_intercept(struct kvm_vcpu *vcpu)
* KVM's capabilities are constrained based on KVM support, i.e. KVM's
* capabilities themselves may be a subset of hardware capabilities.
*/
- return kvm_gp_pmc_mask(pmu) != BIT_ULL(kvm_host_pmu.num_counters_gp) - 1 ||
- kvm_fixed_pmc_mask(pmu) != BIT_ULL(kvm_host_pmu.num_counters_fixed) - 1;
+ return kvm_gp_pmc_mask(pmu) != kvm_host_pmu.cntr_mask64 ||
+ kvm_fixed_pmc_mask(pmu) != kvm_host_pmu.fixed_cntr_mask64;
}
bool kvm_need_perf_global_ctrl_intercept(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index 0943ccc1d6b8..fb5a298244ec 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -203,7 +203,7 @@ static void amd_pmu_refresh(struct kvm_vcpu *vcpu)
}
pmu->pmc_exists64 = (BIT_ULL(nr_gp_counters) - 1) &
- (BIT_ULL(kvm_pmu_cap.num_counters_gp) - 1);
+ kvm_pmu_cap.cntr_mask64;
if (pmu->version > 1) {
pmu->global_ctrl_rsvd = ~pmu->pmc_exists64;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e21abcedea70..c9ed6a6e8325 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -773,7 +773,7 @@ static void svm_recalc_pmu_msr_intercepts(struct kvm_vcpu *vcpu)
MSR_TYPE_RW, intercept || !test_bit(i, &gp_mask));
intercept |= !guest_cpu_cap_has(vcpu, X86_FEATURE_PERFCTR_CORE);
- for (i = 0; i < kvm_pmu_cap.num_counters_gp; i++)
+ for_each_set_bit(i, kvm_host_pmu.cntr_mask, AMD64_NUM_COUNTERS_CORE)
svm_set_intercept_for_msr(vcpu, MSR_F15H_PERF_CTR + 2 * i,
MSR_TYPE_RW, intercept || !test_bit(i, &gp_mask));
@@ -5719,9 +5719,8 @@ static __init void svm_set_cpu_caps(void)
* access to enough counters to virtualize "core" support,
* otherwise limit vPMU support to the legacy number of counters.
*/
- if (kvm_pmu_cap.num_counters_gp < AMD64_NUM_COUNTERS_CORE)
- kvm_pmu_cap.num_counters_gp = min(AMD64_NUM_COUNTERS,
- kvm_pmu_cap.num_counters_gp);
+ if (hweight64(kvm_pmu_cap.cntr_mask64) < AMD64_NUM_COUNTERS_CORE)
+ kvm_pmu_cap.cntr_mask64 &= GENMASK_ULL(AMD64_NUM_COUNTERS - 1, 0);
else
kvm_cpu_cap_check_and_set(X86_FEATURE_PERFCTR_CORE);
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 7770200d0e91..ce668ea08da5 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -494,7 +494,8 @@ static __always_inline u64 intel_get_fixed_pmc_eventsel(unsigned int index)
* have a known encoding for the associated general purpose event.
*/
eventsel = perf_get_hw_event_config(fixed_pmc_perf_ids[index]);
- WARN_ON_ONCE(!eventsel && index < kvm_pmu_cap.num_counters_fixed);
+ WARN_ON_ONCE(!eventsel &&
+ (kvm_pmu_cap.fixed_cntr_mask64 & BIT_ULL(index)));
return eventsel;
}
@@ -516,7 +517,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
union cpuid10_edx edx;
u64 perf_capabilities;
u64 fixed_mask;
- int nr_gp_counters;
+ int nr_gp_counters, nr_fixed_counters;
u64 counter_rsvd;
if (!lbr_desc)
@@ -550,16 +551,25 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
kvm_pmu_cap.events_mask_len);
pmu->available_event_types = ~entry->ebx & (BIT_ULL(eax.split.mask_length) - 1);
- fixed_mask = BIT_ULL(edx.split.num_counters_fixed) - 1;
- fixed_mask &= BIT_ULL(kvm_pmu_cap.num_counters_fixed) - 1;
+ /*
+ * CPUID.0AH:EDX[4:0] can only enumerate contiguous counters. Clamp the
+ * value to the number of contiguous fixed counters supported by KVM.
+ */
+ nr_fixed_counters = min_t(int, edx.split.num_counters_fixed,
+ find_first_zero_bit(kvm_pmu_cap.fixed_cntr_mask,
+ KVM_MAX_NR_FIXED_COUNTERS));
+
+ fixed_mask = BIT_ULL(nr_fixed_counters) - 1;
+ fixed_mask &= kvm_pmu_cap.fixed_cntr_mask64;
/*
- * The number of counters comes from guest CPUID data. Clamp the value
- * to avoid a shift-by-64 in BIT_ULL().
+ * CPUID.0AH:EAX[15:8] can only enumerate contiguous counters. Clamp the
+ * value to the number of contiguous GP counters supported by KVM.
*/
- nr_gp_counters = min_t(int, eax.split.num_counters, X86_PMC_IDX_MAX - 1);
- pmu->pmc_exists64 = (BIT_ULL(nr_gp_counters) - 1) &
- (BIT_ULL(kvm_pmu_cap.num_counters_gp) - 1);
+ nr_gp_counters = min_t(int, eax.split.num_counters,
+ find_first_zero_bit(kvm_pmu_cap.cntr_mask,
+ KVM_MAX_NR_GP_COUNTERS));
+ pmu->pmc_exists64 = BIT_ULL(nr_gp_counters) - 1;
entry = kvm_find_cpuid_entry_index(vcpu, 7, 0);
if (entry &&
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 944ecbf351cf..9db6107943ec 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4264,7 +4264,7 @@ static void vmx_recalc_pmu_msr_intercepts(struct kvm_vcpu *vcpu)
vm_exit_controls_changebit(vmx, vm_exit_controls_bits, has_mediated_pmu);
- for (i = 0; i < kvm_pmu_cap.num_counters_gp; i++) {
+ for_each_set_bit(i, kvm_host_pmu.cntr_mask, INTEL_PMC_MAX_GENERIC) {
bool pmc_intercept = intercept || !test_bit(i, &gp_mask);
vmx_set_intercept_for_msr(vcpu, MSR_IA32_PERFCTR0 + i,
@@ -4273,7 +4273,7 @@ static void vmx_recalc_pmu_msr_intercepts(struct kvm_vcpu *vcpu)
pmc_intercept || !fw_writes_is_enabled(vcpu));
}
- for (i = 0; i < kvm_pmu_cap.num_counters_fixed; i++) {
+ for_each_set_bit(i, kvm_host_pmu.fixed_cntr_mask, INTEL_PMC_MAX_FIXED) {
bool pmc_intercept = intercept || !test_bit(i, &fixed_mask);
vmx_set_intercept_for_msr(vcpu, MSR_CORE_PERF_FIXED_CTR0 + i,
--
2.56.0