Re: [PATCH v12 6/8] arm64: KVM: Enable VHE support for :G/:H perf event modifiers

From: Will Deacon <will.deacon@arm.com>
To: Andrew Murray <andrew.murray@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Julien Thierry <julien.thierry@arm.com>,
	Christoffer Dall <christoffer.dall@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v12 6/8] arm64: KVM: Enable VHE support for :G/:H perf event modifiers
Date: Tue, 9 Apr 2019 18:52:27 +0100	[thread overview]
Message-ID: <20190409175227.GD9255@fuggles.cambridge.arm.com> (raw)
In-Reply-To: <20190328103731.27264-7-andrew.murray@arm.com>

On Thu, Mar 28, 2019 at 10:37:29AM +0000, 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@arm.com>
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> ---
>  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 427c28be6452..481411295b3b 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -365,6 +365,9 @@ 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 a3bfb75f0be9..4f290dad3a48 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -528,7 +528,7 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu);
>  
>  static inline bool kvm_pmu_counter_deferred(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 */
> @@ -542,6 +542,9 @@ 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 6bb28aaf5aea..314b1adedf06 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;

I still don't really like these semantics, but it's consistent and
you're documenting it so:

Acked-by: Will Deacon <will.deacon@arm.com>

Will

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