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

From: Andrew Murray <andrew.murray@arm.com>
To: Will Deacon <will.deacon@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 20:13:51 +0100	[thread overview]
Message-ID: <20190409191350.GC25919@e119886-lin.cambridge.arm.com> (raw)
In-Reply-To: <20190409175227.GD9255@fuggles.cambridge.arm.com>

On Tue, Apr 09, 2019 at 06:52:27PM +0100, Will Deacon wrote:
> 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>

Much appreciated.

Thanks,

Andrew Murray

> 
> Will

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