Re: [PATCH v10 5/5] arm64: KVM: Enable support for :G/:H perf event modifiers

[Andrew Murray <andrew.murray@arm.com>]

On Mon, Feb 18, 2019 at 11:00:19PM +0100, Christoffer Dall wrote:
> On Mon, Jan 14, 2019 at 04:11:48PM +0000, Andrew Murray wrote:
> > Enable/disable event counters as appropriate when entering and exiting
> > the guest to enable support for guest or host only event counting.
> > 
> > For both VHE and non-VHE we switch the counters between host/guest at
> > EL2. EL2 is filtered out by the PMU when we are using the :G modifier.
> 
> I don't think the last part is strictly true as per the former patch on
> a non-vhe system if you have the :h modifier, so maybe just leave that
> out of the commit message.

OK I'll remove that.

> 
> > 
> > The PMU may be on when we change which counters are enabled however
> > we avoid adding an isb as we instead rely on existing context
> > synchronisation events: the isb in kvm_arm_vhe_guest_exit for VHE and
> > the eret from the hvc in kvm_call_hyp.
> > 
> > Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> > Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > ---
> >  arch/arm64/kvm/hyp/switch.c | 60 +++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 60 insertions(+)
> > 
> > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> > index b0b1478..9018fb3 100644
> > --- a/arch/arm64/kvm/hyp/switch.c
> > +++ b/arch/arm64/kvm/hyp/switch.c
> > @@ -357,6 +357,54 @@ static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu)
> >  	return true;
> >  }
> >  
> > +static bool __hyp_text __pmu_switch_to_guest(struct kvm_cpu_context *host_ctxt)
> > +{
> > +	struct kvm_host_data *host;
> > +	struct kvm_pmu_events *pmu;
> > +	u32 clr, set;
> > +
> > +	host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
> > +	pmu = &host->pmu_events;
> > +
> > +	/* We can potentially avoid a sysreg write by only changing bits that
> > +	 * differ between the guest/host. E.g. where events are enabled in
> > +	 * both guest and host
> > +	 */
> 
> super nit: kernel coding style requires 'wings' on both side of a
> multi-line comment.  Only if you respin anyhow.

Ah I didn't notice that, I'll fix this up.

Thanks for the review.

Andrew Murray

> 
> > +	clr = pmu->events_host & ~pmu->events_guest;
> > +	set = pmu->events_guest & ~pmu->events_host;
> > +
> > +	if (clr)
> > +		write_sysreg(clr, pmcntenclr_el0);
> > +
> > +	if (set)
> > +		write_sysreg(set, pmcntenset_el0);
> > +
> > +	return (clr || set);
> > +}
> > +
> > +static void __hyp_text __pmu_switch_to_host(struct kvm_cpu_context *host_ctxt)
> > +{
> > +	struct kvm_host_data *host;
> > +	struct kvm_pmu_events *pmu;
> > +	u32 clr, set;
> > +
> > +	host = container_of(host_ctxt, struct kvm_host_data, host_ctxt);
> > +	pmu = &host->pmu_events;
> > +
> > +	/* We can potentially avoid a sysreg write by only changing bits that
> > +	 * differ between the guest/host. E.g. where events are enabled in
> > +	 * both guest and host
> > +	 */
> 
> ditto
> 
> > +	clr = pmu->events_guest & ~pmu->events_host;
> > +	set = pmu->events_host & ~pmu->events_guest;
> > +
> > +	if (clr)
> > +		write_sysreg(clr, pmcntenclr_el0);
> > +
> > +	if (set)
> > +		write_sysreg(set, pmcntenset_el0);
> > +}
> > +
> >  /*
> >   * Return true when we were able to fixup the guest exit and should return to
> >   * the guest, false when we should restore the host state and return to the
> > @@ -464,12 +512,15 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> >  {
> >  	struct kvm_cpu_context *host_ctxt;
> >  	struct kvm_cpu_context *guest_ctxt;
> > +	bool pmu_switch_needed;
> >  	u64 exit_code;
> >  
> >  	host_ctxt = vcpu->arch.host_cpu_context;
> >  	host_ctxt->__hyp_running_vcpu = vcpu;
> >  	guest_ctxt = &vcpu->arch.ctxt;
> >  
> > +	pmu_switch_needed = __pmu_switch_to_guest(host_ctxt);
> > +
> >  	sysreg_save_host_state_vhe(host_ctxt);
> >  
> >  	/*
> > @@ -511,6 +562,9 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> >  
> >  	__debug_switch_to_host(vcpu);
> >  
> > +	if (pmu_switch_needed)
> > +		__pmu_switch_to_host(host_ctxt);
> > +
> >  	return exit_code;
> >  }
> >  
> > @@ -519,6 +573,7 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
> >  {
> >  	struct kvm_cpu_context *host_ctxt;
> >  	struct kvm_cpu_context *guest_ctxt;
> > +	bool pmu_switch_needed;
> >  	u64 exit_code;
> >  
> >  	vcpu = kern_hyp_va(vcpu);
> > @@ -527,6 +582,8 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
> >  	host_ctxt->__hyp_running_vcpu = vcpu;
> >  	guest_ctxt = &vcpu->arch.ctxt;
> >  
> > +	pmu_switch_needed = __pmu_switch_to_guest(host_ctxt);
> > +
> >  	__sysreg_save_state_nvhe(host_ctxt);
> >  
> >  	__activate_vm(kern_hyp_va(vcpu->kvm));
> > @@ -573,6 +630,9 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
> >  	 */
> >  	__debug_switch_to_host(vcpu);
> >  
> > +	if (pmu_switch_needed)
> > +		__pmu_switch_to_host(host_ctxt);
> > +
> >  	return exit_code;
> >  }
> >  
> > -- 
> > 2.7.4
> > 
> 
> Thanks,
> 
>     Christoffer

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