[PATCH v6 6/8] KVM: x86/pmu: Move RDPMC emulation into per-vendor callbacks
From: Zide Chen
Date: Mon Jun 29 2026 - 19:32:24 EST
The current RDPMC emulation splits responsibility: rdpmc_ecx_to_pmc()
in each vendor returns a kvm_pmc, then common code calls
pmc_read_counter().
This design cannot support RDPMC reads that don't map to a counter,
such as PERF_METRICS on Intel platforms.
Replace rdpmc_ecx_to_pmc() with emulate_rdpmc(), which takes full
ownership of the emulation and writes the result directly into @data.
Also drop the redundant bitmask in intel_emulate_rdpmc() since
pmc_read_counter() already applies the counter's bit-width mask.
No functional change intended.
Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
---
v6: new patch.
---
arch/x86/include/asm/kvm-x86-pmu-ops.h | 2 +-
arch/x86/kvm/pmu.c | 9 +--------
arch/x86/kvm/pmu.h | 4 ++--
arch/x86/kvm/svm/pmu.c | 13 +++++++++----
arch/x86/kvm/vmx/pmu_intel.c | 25 ++++++++++++-------------
5 files changed, 25 insertions(+), 28 deletions(-)
diff --git a/arch/x86/include/asm/kvm-x86-pmu-ops.h b/arch/x86/include/asm/kvm-x86-pmu-ops.h
index 4a223c2793e3..4b50ed058aed 100644
--- a/arch/x86/include/asm/kvm-x86-pmu-ops.h
+++ b/arch/x86/include/asm/kvm-x86-pmu-ops.h
@@ -13,7 +13,7 @@
* KVM_X86_PMU_OP_OPTIONAL() can be used for those functions that can have
* a NULL definition.
*/
-KVM_X86_PMU_OP(rdpmc_ecx_to_pmc)
+KVM_X86_PMU_OP(emulate_rdpmc)
KVM_X86_PMU_OP(msr_idx_to_pmc)
KVM_X86_PMU_OP_OPTIONAL(check_rdpmc_early)
KVM_X86_PMU_OP(is_valid_msr)
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index f82ba63767d0..8ef2d4761790 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -768,8 +768,6 @@ static int kvm_pmu_rdpmc_vmware(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
{
struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
- struct kvm_pmc *pmc;
- u64 mask = ~0ull;
if (!pmu->version)
return 1;
@@ -777,17 +775,12 @@ int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
if (is_vmware_backdoor_pmc(idx))
return kvm_pmu_rdpmc_vmware(vcpu, idx, data);
- pmc = kvm_pmu_call(rdpmc_ecx_to_pmc)(vcpu, idx, &mask);
- if (!pmc)
- return 1;
-
if (!kvm_is_cr4_bit_set(vcpu, X86_CR4_PCE) &&
(kvm_x86_call(get_cpl)(vcpu) != 0) &&
kvm_is_cr0_bit_set(vcpu, X86_CR0_PE))
return 1;
- *data = pmc_read_counter(pmc) & mask;
- return 0;
+ return kvm_pmu_call(emulate_rdpmc)(vcpu, idx, data);
}
static bool kvm_need_any_pmc_intercept(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index 3066cade5790..cdbefda844b9 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -24,8 +24,8 @@
#define KVM_FIXED_PMC_BASE_IDX INTEL_PMC_IDX_FIXED
struct kvm_pmu_ops {
- struct kvm_pmc *(*rdpmc_ecx_to_pmc)(struct kvm_vcpu *vcpu,
- unsigned int idx, u64 *mask);
+ int (*emulate_rdpmc)(struct kvm_vcpu *vcpu, unsigned int idx,
+ u64 *data);
struct kvm_pmc *(*msr_idx_to_pmc)(struct kvm_vcpu *vcpu, u32 msr);
int (*check_rdpmc_early)(struct kvm_vcpu *vcpu, unsigned int idx);
bool (*is_valid_msr)(struct kvm_vcpu *vcpu, u32 msr);
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index c18286545a7a..0517fd4bbcd7 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -84,10 +84,15 @@ static int amd_check_rdpmc_early(struct kvm_vcpu *vcpu, unsigned int idx)
}
/* idx is the ECX register of RDPMC instruction */
-static struct kvm_pmc *amd_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
- unsigned int idx, u64 *mask)
+static int amd_emulate_rdpmc(struct kvm_vcpu *vcpu, unsigned int idx, u64 *data)
{
- return amd_pmu_get_pmc(vcpu_to_pmu(vcpu), idx);
+ struct kvm_pmc *pmc = amd_pmu_get_pmc(vcpu_to_pmu(vcpu), idx);
+
+ if (!pmc)
+ return 1;
+
+ *data = pmc_read_counter(pmc);
+ return 0;
}
static struct kvm_pmc *amd_msr_idx_to_pmc(struct kvm_vcpu *vcpu, u32 msr)
@@ -302,7 +307,7 @@ static bool amd_pmc_is_disabled_in_current_mode(struct kvm_pmc *pmc)
}
struct kvm_pmu_ops amd_pmu_ops __initdata = {
- .rdpmc_ecx_to_pmc = amd_rdpmc_ecx_to_pmc,
+ .emulate_rdpmc = amd_emulate_rdpmc,
.msr_idx_to_pmc = amd_msr_idx_to_pmc,
.check_rdpmc_early = amd_check_rdpmc_early,
.is_valid_msr = amd_is_valid_msr,
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 225afd3937c3..080677372c9b 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -84,14 +84,13 @@ static void reprogram_fixed_counters(struct kvm_pmu *pmu, u64 data)
}
}
-static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
- unsigned int idx, u64 *mask)
+static int intel_emulate_rdpmc(struct kvm_vcpu *vcpu, unsigned int idx,
+ u64 *data)
{
unsigned int type = idx & INTEL_RDPMC_TYPE_MASK;
struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
- struct kvm_pmc *counters;
+ struct kvm_pmc *counters, *pmc;
unsigned int num_counters;
- u64 bitmask;
/*
* The encoding of ECX for RDPMC is different for architectural versus
@@ -104,7 +103,9 @@ static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
* as KVM doesn't support such PMUs.
*/
if (WARN_ON_ONCE(!pmu->version))
- return NULL;
+ return 1;
+
+ idx &= INTEL_RDPMC_INDEX_MASK;
/*
* General Purpose (GP) PMCs are supported on all PMUs, and fixed PMCs
@@ -118,23 +119,21 @@ static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
case INTEL_RDPMC_FIXED:
counters = pmu->fixed_counters;
num_counters = pmu->nr_arch_fixed_counters;
- bitmask = pmu->counter_bitmask[KVM_PMC_FIXED];
break;
case INTEL_RDPMC_GP:
counters = pmu->gp_counters;
num_counters = pmu->nr_arch_gp_counters;
- bitmask = pmu->counter_bitmask[KVM_PMC_GP];
break;
default:
- return NULL;
+ return 1;
}
- idx &= INTEL_RDPMC_INDEX_MASK;
if (idx >= num_counters)
- return NULL;
+ return 1;
- *mask &= bitmask;
- return &counters[array_index_nospec(idx, num_counters)];
+ pmc = &counters[array_index_nospec(idx, num_counters)];
+ *data = pmc_read_counter(pmc);
+ return 0;
}
static inline struct kvm_pmc *get_fw_gp_pmc(struct kvm_pmu *pmu, u32 msr)
@@ -865,7 +864,7 @@ static void intel_mediated_pmu_put(struct kvm_vcpu *vcpu)
}
struct kvm_pmu_ops intel_pmu_ops __initdata = {
- .rdpmc_ecx_to_pmc = intel_rdpmc_ecx_to_pmc,
+ .emulate_rdpmc = intel_emulate_rdpmc,
.msr_idx_to_pmc = intel_msr_idx_to_pmc,
.is_valid_msr = intel_is_valid_msr,
.get_msr = intel_pmu_get_msr,
--
2.54.0