[PATCH v7 16/20] KVM: arm64: Detect overflows for the Partitioned PMU

Colton Lewis
2026-05-04T21:19:07Z

When we re-enter the VM after handling a PMU interrupt, calculate
whether it was any of the guest counters that overflowed and inject an
interrupt into the guest if so.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
arch/arm64/kvm/pmu-direct.c | 30 ++++++++++++++++++++++++++++++
arch/arm64/kvm/pmu-emul.c | 4 ++--
arch/arm64/kvm/pmu.c | 6 +++++-
include/kvm/arm_pmu.h | 2 ++
4 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/pmu-direct.c b/arch/arm64/kvm/pmu-direct.c
index 535b4c492ff80..9693d9eb69daa 100644
--- a/arch/arm64/kvm/pmu-direct.c
+++ b/arch/arm64/kvm/pmu-direct.c
@@ -433,3 +433,33 @@ void kvm_pmu_handle_guest_irq(struct arm_pmu *pmu, u64 pmovsr)

__vcpu_rmw_sys_reg(vcpu, PMOVSSET_EL0, |=, govf);
}
+
+/**
+ * kvm_pmu_part_overflow_status() - Determine if any guest counters have overflowed
+ * @vcpu: Pointer to struct kvm_vcpu
+ *
+ * Determine if any guest counters have overflowed and therefore an
+ * IRQ needs to be injected into the guest. If access is still free,
+ * then the guest hasn't accessed the PMU yet so we know the guest
+ * context is not loaded onto the pCPU and an overflow is impossible.
+ *
+ * Return: True if there was an overflow, false otherwise
+ */
+bool kvm_pmu_part_overflow_status(struct kvm_vcpu *vcpu)
+{
+ struct arm_pmu *pmu;
+ u64 mask, pmovs, pmint, pmcr;
+ bool overflow;
+
+ if (vcpu->arch.pmu.access == VCPU_PMU_ACCESS_FREE)
+ return false;
+
+ pmu = vcpu->kvm->arch.arm_pmu;
+ mask = kvm_pmu_guest_counter_mask(pmu);
+ pmovs = __vcpu_sys_reg(vcpu, PMOVSSET_EL0);
+ pmint = read_pmintenset();
+ pmcr = read_pmcr();
+ overflow = (pmcr & ARMV8_PMU_PMCR_E) && (mask & pmovs & pmint);
+
+ return overflow;
+}
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index a40db0d5120ff..c5438de3e5a74 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -268,7 +268,7 @@ void kvm_pmu_reprogram_counter_mask(struct kvm_vcpu *vcpu, u64 val)
* counter where the values of the global enable control, PMOVSSET_EL0[n], and
* PMINTENSET_EL1[n] are all 1.
*/
-bool kvm_pmu_overflow_status(struct kvm_vcpu *vcpu)
+bool kvm_pmu_emul_overflow_status(struct kvm_vcpu *vcpu)
{
u64 reg = __vcpu_sys_reg(vcpu, PMOVSSET_EL0);

@@ -405,7 +405,7 @@ static void kvm_pmu_perf_overflow(struct perf_event *perf_event,
kvm_pmu_counter_increment(vcpu, BIT(idx + 1),
ARMV8_PMUV3_PERFCTR_CHAIN);

- if (kvm_pmu_overflow_status(vcpu)) {
+ if (kvm_pmu_emul_overflow_status(vcpu)) {
kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);

if (!in_nmi())
diff --git a/arch/arm64/kvm/pmu.c b/arch/arm64/kvm/pmu.c
index 8c10ad05661bc..f1c66ce678840 100644
--- a/arch/arm64/kvm/pmu.c
+++ b/arch/arm64/kvm/pmu.c
@@ -408,7 +408,11 @@ static void kvm_pmu_update_state(struct kvm_vcpu *vcpu)
struct kvm_pmu *pmu = &vcpu->arch.pmu;
bool overflow;

- overflow = kvm_pmu_overflow_status(vcpu);
+ if (kvm_vcpu_pmu_is_partitioned(vcpu))
+ overflow = kvm_pmu_part_overflow_status(vcpu);
+ else
+ overflow = kvm_pmu_emul_overflow_status(vcpu);
+
if (pmu->irq_level == overflow)
return;

diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index de058a5347d18..4af8abf2dde0f 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h
@@ -90,6 +90,8 @@ bool kvm_set_pmuserenr(u64 val);
void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu);
void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu);
void kvm_vcpu_pmu_resync_el0(void);
+bool kvm_pmu_emul_overflow_status(struct kvm_vcpu *vcpu);
+bool kvm_pmu_part_overflow_status(struct kvm_vcpu *vcpu);

#define kvm_vcpu_has_pmu(vcpu) \
(vcpu_has_feature(vcpu, KVM_ARM_VCPU_PMU_V3))
--
2.54.0.545.g6539524ca2-goog