Re: [PATCH 2/2] xen/arm: drop incorrect EL0 accessibility comments for PMINTEN{SET,CLR}

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 11 Aug 2026, Michal Orzel wrote:
> The comments on the PMINTENSET/PMINTENCLR cases claim that an EL0 access
> may be trapped to EL2 when MDCR_EL2.TPM is set, and that such a case is
> handled. Both are inaccurate. PMINTENSET_EL1/PMINTENCLR_EL1 are accessible
> at EL1 and above only, with no enable making them accessible at EL0.
> 
> Arm ARM (DDI 0487M.b) D1.4.5.6 "Prioritization of Synchronous
> exceptions" orders the two exceptions. An access that is never
> accessible at the current Exception level regardless of any enables or
> traps is priority 18, whereas an exception taken to EL2 as the result of
> a configuration control in MDCR_EL2 is priority 24. An EL0 access is
> therefore UNDEFINED and taken to EL1.
> 
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>  xen/arch/arm/arm64/vsysreg.c | 4 ----
>  xen/arch/arm/vcpreg.c        | 1 -
>  2 files changed, 5 deletions(-)
> 
> diff --git a/xen/arch/arm/arm64/vsysreg.c b/xen/arch/arm/arm64/vsysreg.c
> index a59848889659..2ada791f4ea7 100644
> --- a/xen/arch/arm/arm64/vsysreg.c
> +++ b/xen/arch/arm/arm64/vsysreg.c
> @@ -228,10 +228,6 @@ void do_sysreg(struct cpu_user_regs *regs,
>       */
>      case HSR_SYSREG_PMINTENSET_EL1:
>      case HSR_SYSREG_PMINTENCLR_EL1:
> -        /*
> -         * Accessible from EL1 only, but if EL0 trap happens handle as
> -         * undef.
> -         */
>          return handle_raz_wi(regs, regidx, hsr.sysreg.read, hsr, 1);
>      case HSR_SYSREG_PMUSERENR_EL0:
>          /* RO at EL0. RAZ/WI at EL1 */
> diff --git a/xen/arch/arm/vcpreg.c b/xen/arch/arm/vcpreg.c
> index 749ce6d3a57c..b0f3c7759a04 100644
> --- a/xen/arch/arm/vcpreg.c
> +++ b/xen/arch/arm/vcpreg.c
> @@ -295,7 +295,6 @@ void do_cp15_32(struct cpu_user_regs *regs, const union 
> hsr hsr)
>              return handle_raz_wi(regs, regidx, cp32.read, hsr, 1);
>      case HSR_CPREG32(PMINTENSET):
>      case HSR_CPREG32(PMINTENCLR):
> -        /* EL1 only, however MDCR_EL2.TPM==1 means EL0 may trap here also. */
>          return handle_raz_wi(regs, regidx, cp32.read, hsr, 1);
>      case HSR_CPREG32(PMCR):
>      case HSR_CPREG32(PMCNTENSET):
> -- 
> 2.43.0
>