Hi Andrew,
On 08/03/2019 12:07, Andrew Murray wrote:
> With VHE different exception levels are used between the host (EL2) and
> guest (EL1) with a shared exception level for userpace (EL0). We can take
> advantage of this and use the PMU's exception level filtering to avoid
> enabling/disabling counters in the world-switch code. Instead we just
> modify the counter type to include or exclude EL0 at vcpu_{load,put} time.
>
> We also ensure that trapped PMU system register writes do not re-enable
> EL0 when reconfiguring the backing perf events.
>
> This approach completely avoids blackout windows seen with !VHE.
>
> Suggested-by: Christoffer Dall <christoffer.dall@xxxxxxx>
> Signed-off-by: Andrew Murray <andrew.murray@xxxxxxx>
> ---
> arch/arm/include/asm/kvm_host.h | 3 ++
> arch/arm64/include/asm/kvm_host.h | 5 +-
> arch/arm64/kernel/perf_event.c | 6 ++-
> arch/arm64/kvm/pmu.c | 87 ++++++++++++++++++++++++++++++-
> arch/arm64/kvm/sys_regs.c | 3 ++
> virt/kvm/arm/arm.c | 2 +
> 6 files changed, 102 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index a358cb15bb0d..3ce429954306 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -326,6 +326,9 @@ static inline void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) {}
> static inline void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu) {}
> static inline void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) {}
>
> +static inline void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu) {}
> +static inline void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu) {}
> +
> static inline void kvm_arm_vhe_guest_enter(void) {}
> static inline void kvm_arm_vhe_guest_exit(void) {}
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 7ca4e094626d..d631528898b5 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -487,7 +487,7 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu);
>
> static inline bool kvm_pmu_counter_defered(struct perf_event_attr *attr)
> {
> - return attr->exclude_host;
> + return (!has_vhe() && attr->exclude_host);
> }
>
> #ifdef CONFIG_KVM /* Avoid conflicts with core headers if CONFIG_KVM=n */
> @@ -501,6 +501,9 @@ void kvm_clr_pmu_events(u32 clr);
>
> void __pmu_switch_to_host(struct kvm_cpu_context *host_ctxt);
> bool __pmu_switch_to_guest(struct kvm_cpu_context *host_ctxt);
> +
> +void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu);
> +void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu);
> #else
> static inline void kvm_set_pmu_events(u32 set, struct perf_event_attr *attr) {}
> static inline void kvm_clr_pmu_events(u32 clr) {}
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index 64f02a9fd7cd..a121a82fc54c 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -847,8 +847,12 @@ static int armv8pmu_set_event_filter(struct hw_perf_event *event,
> * with other architectures (x86 and Power).
> */
> if (is_kernel_in_hyp_mode()) {
> - if (!attr->exclude_kernel)
> + if (!attr->exclude_kernel && !attr->exclude_host)
> config_base |= ARMV8_PMU_INCLUDE_EL2;
> + if (attr->exclude_guest)
> + config_base |= ARMV8_PMU_EXCLUDE_EL1;
> + if (attr->exclude_host)
> + config_base |= ARMV8_PMU_EXCLUDE_EL0;
> } else {
> if (!attr->exclude_hv && !attr->exclude_host)
> config_base |= ARMV8_PMU_INCLUDE_EL2;
> diff --git a/arch/arm64/kvm/pmu.c b/arch/arm64/kvm/pmu.c
> index a1cee7919953..a0830c70ece5 100644
> --- a/arch/arm64/kvm/pmu.c
> +++ b/arch/arm64/kvm/pmu.c
> @@ -12,11 +12,19 @@
> DECLARE_PER_CPU(kvm_host_data_t, kvm_host_data);
>
> /*
> - * Given the exclude_{host,guest} attributes, determine if we are going
> - * to need to switch counters at guest entry/exit.
> + * Given the perf event attributes and system type, determine
> + * if we are going to need to switch counters at guest entry/exit.
> */
> static bool kvm_pmu_switch_needed(struct perf_event_attr *attr)
> {
> + /**
> + * With VHE the guest kernel runs at EL1 and the host at EL2,
> + * where user (EL0) is excluded then we have no reason to switch
> + * counters.
> + */
> + if (has_vhe() && attr->exclude_user)
> + return false;
> +
> /* Only switch if attributes are different */
> return (attr->exclude_host ^ attr->exclude_guest);
> }
> @@ -87,3 +95,78 @@ void __hyp_text __pmu_switch_to_host(struct kvm_cpu_context *host_ctxt)
> write_sysreg(pmu->events_host, pmcntenset_el0);
> }
>
> +/*
> + * Modify ARMv8 PMU events to include EL0 counting
> + */
> +static void kvm_vcpu_pmu_enable_el0(unsigned long events)
> +{
> + u64 typer;
> + u32 counter;
> +
> + for_each_set_bit(counter, &events, 32) {
> + write_sysreg(counter, pmselr_el0);
> + isb();
> + typer = read_sysreg(pmxevtyper_el0) & ~ARMV8_PMU_EXCLUDE_EL0;
> + write_sysreg(typer, pmxevtyper_el0);
> + isb();
> + }
> +}
> +
> +/*
> + * Modify ARMv8 PMU events to exclude EL0 counting
> + */
> +static void kvm_vcpu_pmu_disable_el0(unsigned long events)
> +{
> + u64 typer;
> + u32 counter;
> +
> + for_each_set_bit(counter, &events, 32) {
> + write_sysreg(counter, pmselr_el0);
> + isb();
> + typer = read_sysreg(pmxevtyper_el0) | ARMV8_PMU_EXCLUDE_EL0;
> + write_sysreg(typer, pmxevtyper_el0);
> + isb();
> + }
> +}
> +
> +/*
> + * On VHE ensure that only guest events have EL0 counting enabled
> + */
> +void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_cpu_context *host_ctxt;
> + struct kvm_host_data *host;
> + u32 events_guest, events_host;
> +
> + if (!has_vhe())
> + return;
> +
> + host_ctxt = vcpu->arch.host_cpu_context;
> + host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
> + events_guest = host->pmu_events.events_guest;
> + events_host = host->pmu_events.events_host;
> +
> + kvm_vcpu_pmu_enable_el0(events_guest);
> + kvm_vcpu_pmu_disable_el0(events_host);
So, we load a vcpu, and all events common to the guest and the host
(events_guest & events_host) get the EXCLUDE_EL0 flag set.
I don't see anything that will remove that flag before running the
guest. Am I missing something? Should these lines be as follows?
kvm_vcpu_pmu_enable_el0(events_guest & events_host);
kvm_vcpu_pmu_enable_el0(events_guest ^ events_host);
> +}
> +
> +/*
> + * On VHE ensure that only guest host have EL0 counting enabled
> + */
> +void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_cpu_context *host_ctxt;
> + struct kvm_host_data *host;
> + u32 events_guest, events_host;
> +
> + if (!has_vhe())
> + return;
> +
> + host_ctxt = vcpu->arch.host_cpu_context;
> + host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
> + events_guest = host->pmu_events.events_guest;
> + events_host = host->pmu_events.events_host;
> +
> + kvm_vcpu_pmu_enable_el0(events_host);
> + kvm_vcpu_pmu_disable_el0(events_guest);
Same question as above, after vcpu_put, it seems we've disabled at EL0
host events that are common to the guest and the host.
Thanks,
--
Julien Thierry
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