[PATCH v6 24/44] KVM: x86/pmu: Introduce eventsel_hw to prepare for pmu event filtering

Sean Christopherson
2025-12-06T00:18:15Z

From: Mingwei Zhang <mizhang@google.com>

Introduce eventsel_hw and fixed_ctr_ctrl_hw to store the actual HW value in
PMU event selector MSRs. In mediated PMU checks events before allowing the
event values written to the PMU MSRs. However, to match the HW behavior,
when PMU event checks fails, KVM should allow guest to read the value back.

This essentially requires an extra variable to separate the guest requested
value from actual PMU MSR value. Note this only applies to event selectors.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Co-developed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Xudong Hao <xudong.hao@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/pmu.c | 7 +++++--
arch/x86/kvm/svm/pmu.c | 1 +
arch/x86/kvm/vmx/pmu_intel.c | 2 ++
4 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index defd979003be..e72357f64b19 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -529,6 +529,7 @@ struct kvm_pmc {
*/
u64 emulated_counter;
u64 eventsel;
+ u64 eventsel_hw;
struct perf_event *perf_event;
struct kvm_vcpu *vcpu;
/*
@@ -557,6 +558,7 @@ struct kvm_pmu {
unsigned nr_arch_fixed_counters;
unsigned available_event_types;
u64 fixed_ctr_ctrl;
+ u64 fixed_ctr_ctrl_hw;
u64 fixed_ctr_ctrl_rsvd;
u64 global_ctrl;
u64 global_status;
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 621722e8cc7e..36eebc1c7e70 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -902,11 +902,14 @@ static void kvm_pmu_reset(struct kvm_vcpu *vcpu)
pmc->counter = 0;
pmc->emulated_counter = 0;

- if (pmc_is_gp(pmc))
+ if (pmc_is_gp(pmc)) {
pmc->eventsel = 0;
+ pmc->eventsel_hw = 0;
+ }
}

- pmu->fixed_ctr_ctrl = pmu->global_ctrl = pmu->global_status = 0;
+ pmu->fixed_ctr_ctrl = pmu->fixed_ctr_ctrl_hw = 0;
+ pmu->global_ctrl = pmu->global_status = 0;

kvm_pmu_call(reset)(vcpu);
}
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index 16c88b2a2eb8..c1ec1962314e 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -166,6 +166,7 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
data &= ~pmu->reserved_bits;
if (data != pmc->eventsel) {
pmc->eventsel = data;
+ pmc->eventsel_hw = data;
kvm_pmu_request_counter_reprogram(pmc);
}
return 0;
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 820da47454d7..855240678300 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -61,6 +61,7 @@ static void reprogram_fixed_counters(struct kvm_pmu *pmu, u64 data)
int i;

pmu->fixed_ctr_ctrl = data;
+ pmu->fixed_ctr_ctrl_hw = data;
for (i = 0; i < pmu->nr_arch_fixed_counters; i++) {
u8 new_ctrl = fixed_ctrl_field(data, i);
u8 old_ctrl = fixed_ctrl_field(old_fixed_ctr_ctrl, i);
@@ -430,6 +431,7 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)

if (data != pmc->eventsel) {
pmc->eventsel = data;
+ pmc->eventsel_hw = data;
kvm_pmu_request_counter_reprogram(pmc);
}
break;
--
2.52.0.223.gf5cc29aaa4-goog