[PATCH 06/11] KVM: arm64: nv: Acceletate EL0 counter accesses from hypervisor context

[Joey Gouly]

On Mon, Dec 02, 2024 at 05:21:29PM +0000, Marc Zyngier wrote:
> Similarly to handling the physical timer accesses early when FEAT_ECV
> causes a trap, we try to handle the physical counter without returning
> to the general sysreg handling.
> 
> More surprisingly, we introduce something similar for the virtual
> counter. Although this isn't necessary yet, it will prove useful on
> systems that have a broken CNTVOFF_EL2 implementation. Yes, they exist.
> 

> Special care is taken to offset reads of the counter with the host's
> CNTPOFF_EL2, as we perform this with TGE clear.

Can you explain this part a bit more? I'm assuming it's somehow related to the
arch_timer_read_cntpct_el0() call.

However I think we're at EL2 inside kvm_hyp_handle_timer(), so reading
CNTPCT_EL0 won't involve CNTPOFF_EL2.

What am I missing/misunderstanding?

> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/hyp/include/hyp/switch.h |  5 +++++
>  arch/arm64/kvm/hyp/vhe/switch.c         | 13 +++++++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index 34f53707892df..30e572de28749 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -501,6 +501,11 @@ static inline bool handle_tx2_tvm(struct kvm_vcpu *vcpu)
>  	return true;
>  }
>  
> +static inline u64 compute_counter_value(struct arch_timer_context *ctxt)
> +{
> +	return arch_timer_read_cntpct_el0() - timer_get_offset(ctxt);
> +}
> +
>  static bool kvm_hyp_handle_cntpct(struct kvm_vcpu *vcpu)
>  {
>  	struct arch_timer_context *ctxt;
> diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
> index b014b0b10bf5d..49815a8a4c9bc 100644
> --- a/arch/arm64/kvm/hyp/vhe/switch.c
> +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> @@ -296,6 +296,13 @@ static bool kvm_hyp_handle_timer(struct kvm_vcpu *vcpu, u64 *exit_code)
>  			val = __vcpu_sys_reg(vcpu, CNTP_CVAL_EL0);
>  		}
>  		break;
> +	case SYS_CNTPCT_EL0:
> +	case SYS_CNTPCTSS_EL0:
> +		/* If !ELIsInHost(EL0), the guest's CNTPOFF_EL2 applies */
> +		val = compute_counter_value(!(vcpu_el2_e2h_is_set(vcpu) &&
> +					      vcpu_el2_tge_is_set(vcpu)) ?
> +					    vcpu_ptimer(vcpu) : vcpu_hptimer(vcpu));
> +		break;
>  	case SYS_CNTV_CTL_EL02:
>  		val = __vcpu_sys_reg(vcpu, CNTV_CTL_EL0);
>  		break;
> @@ -314,6 +321,12 @@ static bool kvm_hyp_handle_timer(struct kvm_vcpu *vcpu, u64 *exit_code)
>  		else
>  			val = __vcpu_sys_reg(vcpu, CNTV_CVAL_EL0);
>  		break;
> +	case SYS_CNTVCT_EL0:
> +	case SYS_CNTVCTSS_EL0:
> +		/* If !ELIsInHost(EL2), the guest's CNTVOFF_EL2 applies */
> +		val = compute_counter_value(!vcpu_el2_e2h_is_set(vcpu) ?
> +					    vcpu_vtimer(vcpu) : vcpu_hvtimer(vcpu));
> +		break;
>  	default:
>  		return false;
>  	}

Thanks,
Joey