Subject: Re: [PATCH v2 08/18] arm64: KVM: add support to save/restore SPE profiling buffer controls

From: Marc Zyngier <[email-masked]>
Date: Sat, 21 Dec 2019 13:57:55 +0000

On Fri, 20 Dec 2019 14:30:15 +0000
Andrew Murray <[email-masked]> wrote:

> From: Sudeep Holla <[email-masked]>
> 
> Currently since we don't support profiling using SPE in the guests,
> we just save the PMSCR_EL1, flush the profiling buffers and disable
> sampling. However in order to support simultaneous sampling both in

Is the sampling actually simultaneous? I don't believe so (the whole
series would be much simpler if it was).

> the host and guests, we need to save and reatore the complete SPE

s/reatore/restore/

> profiling buffer controls' context.
> 
> Let's add the support for the same and keep it disabled for now.
> We can enable it conditionally only if guests are allowed to use
> SPE.
> 
> Signed-off-by: Sudeep Holla <[email-masked]>
> [ Clear PMBSR bit when saving state to prevent spurious interrupts ]
> Signed-off-by: Andrew Murray <[email-masked]>
> ---
>  arch/arm64/kvm/hyp/debug-sr.c | 51 +++++++++++++++++++++++++++++------
>  1 file changed, 43 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
> index 8a70a493345e..12429b212a3a 100644
> --- a/arch/arm64/kvm/hyp/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/debug-sr.c
> @@ -85,7 +85,8 @@
>  	default:	write_debug(ptr[0], reg, 0);			\
>  	}
>  
> -static void __hyp_text __debug_save_spe_nvhe(struct kvm_cpu_context *ctxt)
> +static void __hyp_text
> +__debug_save_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt)

nit: don't split lines like this if you can avoid it. You can put the
full_ctxt parameter on a separate line instead.

>  {
>  	u64 reg;
>  
> @@ -102,22 +103,46 @@ static void __hyp_text __debug_save_spe_nvhe(struct kvm_cpu_context *ctxt)
>  	if (reg & BIT(SYS_PMBIDR_EL1_P_SHIFT))
>  		return;
>  
> -	/* No; is the host actually using the thing? */
> -	reg = read_sysreg_s(SYS_PMBLIMITR_EL1);
> -	if (!(reg & BIT(SYS_PMBLIMITR_EL1_E_SHIFT)))
> +	/* Save the control register and disable data generation */
> +	ctxt->sys_regs[PMSCR_EL1] = read_sysreg_el1(SYS_PMSCR);
> +
> +	if (!ctxt->sys_regs[PMSCR_EL1])

Shouldn't you check the enable bits instead of relying on the whole
thing being zero?

>  		return;
>  
>  	/* Yes; save the control register and disable data generation */
> -	ctxt->sys_regs[PMSCR_EL1] = read_sysreg_el1(SYS_PMSCR);

You've already saved the control register...

>  	write_sysreg_el1(0, SYS_PMSCR);
>  	isb();
>  
>  	/* Now drain all buffered data to memory */
>  	psb_csync();
>  	dsb(nsh);
> +
> +	if (!full_ctxt)
> +		return;
> +
> +	ctxt->sys_regs[PMBLIMITR_EL1] = read_sysreg_s(SYS_PMBLIMITR_EL1);
> +	write_sysreg_s(0, SYS_PMBLIMITR_EL1);
> +
> +	/*
> +	 * As PMBSR is conditionally restored when returning to the host we
> +	 * must ensure the service bit is unset here to prevent a spurious
> +	 * host SPE interrupt from being raised.
> +	 */
> +	ctxt->sys_regs[PMBSR_EL1] = read_sysreg_s(SYS_PMBSR_EL1);
> +	write_sysreg_s(0, SYS_PMBSR_EL1);
> +
> +	isb();
> +
> +	ctxt->sys_regs[PMSICR_EL1] = read_sysreg_s(SYS_PMSICR_EL1);
> +	ctxt->sys_regs[PMSIRR_EL1] = read_sysreg_s(SYS_PMSIRR_EL1);
> +	ctxt->sys_regs[PMSFCR_EL1] = read_sysreg_s(SYS_PMSFCR_EL1);
> +	ctxt->sys_regs[PMSEVFR_EL1] = read_sysreg_s(SYS_PMSEVFR_EL1);
> +	ctxt->sys_regs[PMSLATFR_EL1] = read_sysreg_s(SYS_PMSLATFR_EL1);
> +	ctxt->sys_regs[PMBPTR_EL1] = read_sysreg_s(SYS_PMBPTR_EL1);
>  }
>  
> -static void __hyp_text __debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt)
> +static void __hyp_text
> +__debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt, bool full_ctxt)
>  {
>  	if (!ctxt->sys_regs[PMSCR_EL1])
>  		return;
> @@ -126,6 +151,16 @@ static void __hyp_text __debug_restore_spe_nvhe(struct kvm_cpu_context *ctxt)
>  	isb();
>  
>  	/* Re-enable data generation */
> +	if (full_ctxt) {
> +		write_sysreg_s(ctxt->sys_regs[PMBPTR_EL1], SYS_PMBPTR_EL1);
> +		write_sysreg_s(ctxt->sys_regs[PMBLIMITR_EL1], SYS_PMBLIMITR_EL1);
> +		write_sysreg_s(ctxt->sys_regs[PMSFCR_EL1], SYS_PMSFCR_EL1);
> +		write_sysreg_s(ctxt->sys_regs[PMSEVFR_EL1], SYS_PMSEVFR_EL1);
> +		write_sysreg_s(ctxt->sys_regs[PMSLATFR_EL1], SYS_PMSLATFR_EL1);
> +		write_sysreg_s(ctxt->sys_regs[PMSIRR_EL1], SYS_PMSIRR_EL1);
> +		write_sysreg_s(ctxt->sys_regs[PMSICR_EL1], SYS_PMSICR_EL1);
> +		write_sysreg_s(ctxt->sys_regs[PMBSR_EL1], SYS_PMBSR_EL1);
> +	}
>  	write_sysreg_el1(ctxt->sys_regs[PMSCR_EL1], SYS_PMSCR);
>  }
>  
> @@ -198,7 +233,7 @@ void __hyp_text __debug_restore_host_context(struct kvm_vcpu *vcpu)
>  	guest_ctxt = &vcpu->arch.ctxt;
>  
>  	if (!has_vhe())
> -		__debug_restore_spe_nvhe(host_ctxt);
> +		__debug_restore_spe_nvhe(host_ctxt, false);
>  
>  	if (!(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
>  		return;
> @@ -222,7 +257,7 @@ void __hyp_text __debug_save_host_context(struct kvm_vcpu *vcpu)
>  
>  	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
>  	if (!has_vhe())
> -		__debug_save_spe_nvhe(host_ctxt);
> +		__debug_save_spe_nvhe(host_ctxt, false);
>  }
>  
>  void __hyp_text __debug_save_guest_context(struct kvm_vcpu *vcpu)

So all of this is for non-VHE. What happens in the VHE case?

	M.
-- 
Jazz is not dead. It just smells funny...

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