Subject: Re: [PATCH v14 03/44] arm64: RME: Handle Granule Protection Faults (GPFs)

From: Marc Zyngier <[email-masked]>
Date: Thu, 21 May 2026 13:25:00 +0100

On Wed, 13 May 2026 14:17:11 +0100,
Steven Price <[email-masked]> wrote:
> 
> If the host attempts to access granules that have been delegated for use
> in a realm these accesses will be caught and will trigger a Granule
> Protection Fault (GPF).
> 
> A fault during a page walk signals a bug in the kernel and is handled by
> oopsing the kernel. A non-page walk fault could be caused by user space
> having access to a page which has been delegated to the kernel and will
> trigger a SIGBUS to allow debugging why user space is trying to access a
> delegated page.
> 
> Reviewed-by: Suzuki K Poulose <[email-masked]>
> Reviewed-by: Gavin Shan <[email-masked]>
> Signed-off-by: Steven Price <[email-masked]>
> ---
> Changes since v10:
>  * Don't call arm64_notify_die() in do_gpf() but simply return 1.
> Changes since v2:
>  * Include missing "Granule Protection Fault at level -1"
> ---
>  arch/arm64/mm/fault.c | 28 ++++++++++++++++++++++------
>  1 file changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 0f3c5c7ca054..6358ea4787ba 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -905,6 +905,22 @@ static int do_tag_check_fault(unsigned long far, unsigned long esr,
>  	return 0;
>  }
>  
> +static int do_gpf_ptw(unsigned long far, unsigned long esr, struct pt_regs *regs)
> +{
> +	const struct fault_info *inf = esr_to_fault_info(esr);
> +
> +	die_kernel_fault(inf->name, far, esr, regs);
> +	return 0;
> +}
> +
> +static int do_gpf(unsigned long far, unsigned long esr, struct pt_regs *regs)
> +{
> +	if (!is_el1_instruction_abort(esr) && fixup_exception(regs, esr))
> +		return 0;
> +
> +	return 1;
> +}
> +
>  static const struct fault_info fault_info[] = {
>  	{ do_bad,		SIGKILL, SI_KERNEL,	"ttbr address size fault"	},
>  	{ do_bad,		SIGKILL, SI_KERNEL,	"level 1 address size fault"	},
> @@ -941,12 +957,12 @@ static const struct fault_info fault_info[] = {
>  	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 32"			},
>  	{ do_alignment_fault,	SIGBUS,  BUS_ADRALN,	"alignment fault"		},
>  	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 34"			},
> -	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 35"			},
> -	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 36"			},
> -	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 37"			},
> -	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 38"			},
> -	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 39"			},
> -	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 40"			},
> +	{ do_gpf_ptw,		SIGKILL, SI_KERNEL,	"Granule Protection Fault at level -1" },
> +	{ do_gpf_ptw,		SIGKILL, SI_KERNEL,	"Granule Protection Fault at level 0" },
> +	{ do_gpf_ptw,		SIGKILL, SI_KERNEL,	"Granule Protection Fault at level 1" },
> +	{ do_gpf_ptw,		SIGKILL, SI_KERNEL,	"Granule Protection Fault at level 2" },
> +	{ do_gpf_ptw,		SIGKILL, SI_KERNEL,	"Granule Protection Fault at level 3" },
> +	{ do_gpf,		SIGBUS,  SI_KERNEL,	"Granule Protection Fault not on table walk" },

It wouldn't hurt to align the textual description with what we have
for other fault syndromes:

	"level X granule protection fault (translation table walk)"

for the PTW-trigger faults, and

	"granule protection fault"

for the non PTW case.

Thanks,

	M.

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