Subject: Re: [PATCH v4 09/29] KVM: arm64: use `at s1e1a` for POE

From: Marc Zyngier <[email-masked]>
Date: Wed, 29 May 2024 16:50:46 +0100

On Fri, 03 May 2024 14:01:27 +0100,
Joey Gouly <[email-masked]> wrote:
> 
> FEAT_ATS1E1A introduces a new instruction: `at s1e1a`.
> This is an address translation, without permission checks.
> 
> POE allows read permissions to be removed from S1 by the guest.  This means
> that an `at` instruction could fail, and not get the IPA.
> 
> Switch to using `at s1e1a` so that KVM can get the IPA regardless of S1
> permissions.
> 
> Signed-off-by: Joey Gouly <[email-masked]>
> Cc: Marc Zyngier <[email-masked]>
> Cc: Oliver Upton <[email-masked]>
> Cc: Catalin Marinas <[email-masked]>
> Cc: Will Deacon <[email-masked]>
> ---
>  arch/arm64/kvm/hyp/include/hyp/fault.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/include/hyp/fault.h b/arch/arm64/kvm/hyp/include/hyp/fault.h
> index 487c06099d6f..17df94570f03 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/fault.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/fault.h
> @@ -14,6 +14,7 @@
>  
>  static inline bool __translate_far_to_hpfar(u64 far, u64 *hpfar)
>  {
> +	int ret;
>  	u64 par, tmp;
>  
>  	/*
> @@ -27,7 +28,9 @@ static inline bool __translate_far_to_hpfar(u64 far, u64 *hpfar)
>  	 * saved the guest context yet, and we may return early...
>  	 */
>  	par = read_sysreg_par();
> -	if (!__kvm_at(OP_AT_S1E1R, far))
> +	ret = system_supports_poe() ? __kvm_at(OP_AT_S1E1A, far) :
> +	                              __kvm_at(OP_AT_S1E1R, far);
> +	if (!ret)
>  		tmp = read_sysreg_par();
>  	else
>  		tmp = SYS_PAR_EL1_F; /* back to the guest */

Reviewed-by: Marc Zyngier <[email-masked]>

	M.

-- 
Without deviation from the norm, progress is not possible.