[PATCH v5 27/44] KVM: x86/pmu: Disable RDPMC interception for compatible mediated vPMU

Sean Christopherson
2025-08-06T19:58:19Z

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

Disable RDPMC interception for vCPUs with a mediated vPMU that is
compatible with the host PMU, i.e. that doesn't require KVM emulation of
RDPMC to honor the guest's vCPU model. With a mediated vPMU, all guest
state accessible via RDPMC is loaded into hardware while the guest is
running.

Adust RDPMC interception only for non-TDX guests, as the TDX module is
responsible for managing RDPMC intercepts based on the TD configuration.

Co-developed-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Co-developed-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/pmu.c | 26 ++++++++++++++++++++++++++
arch/x86/kvm/pmu.h | 1 +
arch/x86/kvm/svm/svm.c | 5 +++++
arch/x86/kvm/vmx/vmx.c | 7 +++++++
arch/x86/kvm/x86.c | 1 +
5 files changed, 40 insertions(+)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 680523e9d11e..674f42d083a9 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -712,6 +712,32 @@ int kvm_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned idx, u64 *data)
return 0;
}

+bool kvm_need_rdpmc_intercept(struct kvm_vcpu *vcpu)
+{
+ struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
+
+ if (!kvm_vcpu_has_mediated_pmu(vcpu))
+ return true;
+
+ /*
+ * VMware allows access to these Pseduo-PMCs even when read via RDPMC
+ * in Ring3 when CR4.PCE=0.
+ */
+ if (enable_vmware_backdoor)
+ return true;
+
+ /*
+ * Note! Check *host* PMU capabilities, not KVM's PMU capabilities, as
+ * KVM's capabilities are constrained based on KVM support, i.e. KVM's
+ * capabilities themselves may be a subset of hardware capabilities.
+ */
+ return pmu->nr_arch_gp_counters != kvm_host_pmu.num_counters_gp ||
+ pmu->nr_arch_fixed_counters != kvm_host_pmu.num_counters_fixed ||
+ pmu->counter_bitmask[KVM_PMC_GP] != (BIT_ULL(kvm_host_pmu.bit_width_gp) - 1) ||
+ pmu->counter_bitmask[KVM_PMC_FIXED] != (BIT_ULL(kvm_host_pmu.bit_width_fixed) - 1);
+}
+EXPORT_SYMBOL_GPL(kvm_need_rdpmc_intercept);
+
void kvm_pmu_deliver_pmi(struct kvm_vcpu *vcpu)
{
if (lapic_in_kernel(vcpu)) {
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index e038bce76b9e..6b95e81c078c 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -238,6 +238,7 @@ void kvm_pmu_instruction_retired(struct kvm_vcpu *vcpu);
void kvm_pmu_branch_retired(struct kvm_vcpu *vcpu);

bool is_vmware_backdoor_pmc(u32 pmc_idx);
+bool kvm_need_rdpmc_intercept(struct kvm_vcpu *vcpu);

extern struct kvm_pmu_ops intel_pmu_ops;
extern struct kvm_pmu_ops amd_pmu_ops;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ef7dffc54dca..2d42962b47aa 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1075,6 +1075,11 @@ static void svm_recalc_instruction_intercepts(struct kvm_vcpu *vcpu)
svm->vmcb->control.virt_ext |= VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
}
}
+
+ if (kvm_need_rdpmc_intercept(vcpu))
+ svm_set_intercept(svm, INTERCEPT_RDPMC);
+ else
+ svm_clr_intercept(svm, INTERCEPT_RDPMC);
}

static void svm_recalc_intercepts(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index baea4a9cf74f..2f7db32710e3 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4121,8 +4121,15 @@ static void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
*/
}

+static void vmx_recalc_instruction_intercepts(struct kvm_vcpu *vcpu)
+{
+ exec_controls_changebit(to_vmx(vcpu), CPU_BASED_RDPMC_EXITING,
+ kvm_need_rdpmc_intercept(vcpu));
+}
+
void vmx_recalc_intercepts(struct kvm_vcpu *vcpu)
{
+ vmx_recalc_instruction_intercepts(vcpu);
vmx_recalc_msr_intercepts(vcpu);
}

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 69f5d9deb75f..b8014435c988 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3793,6 +3793,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)

vcpu->arch.perf_capabilities = data;
kvm_pmu_refresh(vcpu);
+ kvm_make_request(KVM_REQ_RECALC_INTERCEPTS, vcpu);
break;
case MSR_IA32_PRED_CMD: {
u64 reserved_bits = ~(PRED_CMD_IBPB | PRED_CMD_SBPB);
--
2.50.1.565.gc32cd1483b-goog