[PATCH v2] KVM: arm64: pmu: Resync EL0 state on counter rotation
Mark Rutland
mark.rutland at arm.com
Mon Aug 21 23:48:28 PDT 2023
On Sun, Aug 20, 2023 at 10:01:08AM +0100, Marc Zyngier wrote:
> 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 <shijie at os.amperecomputing.com>
> Suggested-by: Oliver Upton <oliver.upton at linux.dev>
> Tested_by: Huang Shijie <shijie at os.amperecomputing.com>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> Cc: Leo Yan <leo.yan at linaro.org>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Link: https://lore.kernel.org/r/20230809013953.7692-1-shijie@os.amperecomputing.com
This looks sane to me so:
Acked-by: Mark Rutland <mark.rutland at arm.com>
It doesn't look like we have any PMU patches queued that would conflict, so if
Will's happy I reckon this should go through the KVM/arm64 tree.
Mark.
> ---
>
> Notes:
> V2: Fixed 32bit compilation
>
> 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 f3cd04ff022d..72529f5e2bed 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 d3dd05bbfe23..553040e0e375 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 72dc53a75d1c..978b0411082f 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 121f1a14c829..0eea225fd09a 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 08b3a1bf0ef6..6a3d8176f54a 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 847da6fc2713..3a8a70a60794 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
>
> --
> 2.39.2
>
More information about the linux-arm-kernel
mailing list