From b1f778a223a2a8ad6262e5233cfc3483bcf6e213 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Sun, 20 Aug 2023 10:01:08 +0100 Subject: [PATCH] KVM: arm64: pmu: Resync EL0 state on counter rotation Huang Shijie reports that, when profiling a guest from the host with a number of events that exceeds the number of available counters, the reported counts are wildly inaccurate. Without the counter oversubscription, the reported counts are correct. Their investigation indicates that upon counter rotation (which takes place on the back of a timer interrupt), we fail to re-apply the guest EL0 enabling, leading to the counting of host events instead of guest events. In order to solve this, add yet another hook between the host PMU driver and KVM, re-applying the guest EL0 configuration if the right conditions apply (the host is VHE, we are in interrupt context, and we interrupted a running vcpu). This triggers a new vcpu request which will apply the correct configuration on guest reentry. With this, we have the correct counts, even when the counters are oversubscribed. Reported-by: Huang Shijie Suggested-by: Oliver Upton Tested_by: Huang Shijie Signed-off-by: Marc Zyngier Cc: Leo Yan Cc: Mark Rutland Cc: Will Deacon Link: https://lore.kernel.org/r/20230809013953.7692-1-shijie@os.amperecomputing.com Acked-by: Mark Rutland Link: https://lore.kernel.org/r/20230820090108.177817-1-maz@kernel.org --- arch/arm/include/asm/arm_pmuv3.h | 2 ++ arch/arm64/include/asm/kvm_host.h | 1 + arch/arm64/kvm/arm.c | 3 +++ arch/arm64/kvm/pmu.c | 18 ++++++++++++++++++ drivers/perf/arm_pmuv3.c | 2 ++ include/kvm/arm_pmu.h | 2 ++ 6 files changed, 28 insertions(+) diff --git a/arch/arm/include/asm/arm_pmuv3.h b/arch/arm/include/asm/arm_pmuv3.h index f3cd04ff022df..72529f5e2bed9 100644 --- a/arch/arm/include/asm/arm_pmuv3.h +++ b/arch/arm/include/asm/arm_pmuv3.h @@ -227,6 +227,8 @@ static inline bool kvm_set_pmuserenr(u64 val) return false; } +static inline void kvm_vcpu_pmu_resync_el0(void) {} + /* PMU Version in DFR Register */ #define ARMV8_PMU_DFR_VER_NI 0 #define ARMV8_PMU_DFR_VER_V3P4 0x5 diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index d3dd05bbfe23f..553040e0e3757 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -49,6 +49,7 @@ #define KVM_REQ_RELOAD_GICv4 KVM_ARCH_REQ(4) #define KVM_REQ_RELOAD_PMU KVM_ARCH_REQ(5) #define KVM_REQ_SUSPEND KVM_ARCH_REQ(6) +#define KVM_REQ_RESYNC_PMU_EL0 KVM_ARCH_REQ(7) #define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \ KVM_DIRTY_LOG_INITIALLY_SET) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 72dc53a75d1c8..978b0411082f1 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -803,6 +803,9 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu) kvm_pmu_handle_pmcr(vcpu, __vcpu_sys_reg(vcpu, PMCR_EL0)); + if (kvm_check_request(KVM_REQ_RESYNC_PMU_EL0, vcpu)) + kvm_vcpu_pmu_restore_guest(vcpu); + if (kvm_check_request(KVM_REQ_SUSPEND, vcpu)) return kvm_vcpu_suspend(vcpu); diff --git a/arch/arm64/kvm/pmu.c b/arch/arm64/kvm/pmu.c index 121f1a14c829c..0eea225fd09a7 100644 --- a/arch/arm64/kvm/pmu.c +++ b/arch/arm64/kvm/pmu.c @@ -236,3 +236,21 @@ bool kvm_set_pmuserenr(u64 val) ctxt_sys_reg(hctxt, PMUSERENR_EL0) = val; return true; } + +/* + * If we interrupted the guest to update the host PMU context, make + * sure we re-apply the guest EL0 state. + */ +void kvm_vcpu_pmu_resync_el0(void) +{ + struct kvm_vcpu *vcpu; + + if (!has_vhe() || !in_interrupt()) + return; + + vcpu = kvm_get_running_vcpu(); + if (!vcpu) + return; + + kvm_make_request(KVM_REQ_RESYNC_PMU_EL0, vcpu); +} diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c index 08b3a1bf0ef62..6a3d8176f54a6 100644 --- a/drivers/perf/arm_pmuv3.c +++ b/drivers/perf/arm_pmuv3.c @@ -772,6 +772,8 @@ static void armv8pmu_start(struct arm_pmu *cpu_pmu) /* Enable all counters */ armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E); + + kvm_vcpu_pmu_resync_el0(); } static void armv8pmu_stop(struct arm_pmu *cpu_pmu) diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h index 847da6fc27139..3a8a70a607942 100644 --- a/include/kvm/arm_pmu.h +++ b/include/kvm/arm_pmu.h @@ -74,6 +74,7 @@ int kvm_arm_pmu_v3_enable(struct kvm_vcpu *vcpu); struct kvm_pmu_events *kvm_get_pmu_events(void); 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); #define kvm_vcpu_has_pmu(vcpu) \ (test_bit(KVM_ARM_VCPU_PMU_V3, (vcpu)->arch.features)) @@ -171,6 +172,7 @@ static inline u8 kvm_arm_pmu_get_pmuver_limit(void) { return 0; } +static inline void kvm_vcpu_pmu_resync_el0(void) {} #endif -- 2.30.2