Re: [PATCH RFC v8 04/24] arm64: Introduce por_elx_set_pkey_perms() helper

["David Hildenbrand (Arm)" <david@kernel.org>]

On 5/26/26 13:15, Kevin Brodsky wrote:
> Introduce a helper that sets the permissions of a given pkey
> (POIndex) in the POR_ELx format, and make use of it in
> arch_set_user_pkey_access().
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
> ---
>  arch/arm64/include/asm/por.h |  7 +++++++
>  arch/arm64/mm/mmu.c          | 26 ++++++++++----------------
>  2 files changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/por.h b/arch/arm64/include/asm/por.h
> index d913d5b529e4..bffb4d2b1246 100644
> --- a/arch/arm64/include/asm/por.h
> +++ b/arch/arm64/include/asm/por.h
> @@ -31,4 +31,11 @@ static inline bool por_elx_allows_exec(u64 por, u8 pkey)
>  	return perm & POE_X;
>  }
>  
> +static inline u64 por_elx_set_pkey_perms(u64 por, u8 pkey, u64 perms)
> +{
> +	u64 shift = POR_ELx_PERM_SHIFT(pkey);
> +
> +	return (por & ~(POE_MASK << shift)) | (perms << shift);
> +}
> +
>  #endif /* _ASM_ARM64_POR_H */
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index dd85e093ffdb..493310cf0486 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -2339,8 +2339,8 @@ void __cpu_replace_ttbr1(pgd_t *pgdp, bool cnp)
>  #ifdef CONFIG_ARCH_HAS_PKEYS
>  int arch_set_user_pkey_access(int pkey, unsigned long init_val)
>  {
> -	u64 new_por;
> -	u64 old_por;
> +	u64 new_perms;

You should spell out the renaming of the variable.

Given that perms is 4bit per key, should we use a u8 for it instead?

> +	u64 por;
>  
>  	if (!system_supports_poe())
>  		return -ENOSPC;
> @@ -2354,25 +2354,19 @@ int arch_set_user_pkey_access(int pkey, unsigned long init_val)
>  		return -EINVAL;
>  
>  	/* Set the bits we need in POR:  */
> -	new_por = POE_RWX;
> +	new_perms = POE_RWX;
>  	if (init_val & PKEY_DISABLE_WRITE)
> -		new_por &= ~POE_W;
> +		new_perms &= ~POE_W;
>  	if (init_val & PKEY_DISABLE_ACCESS)
> -		new_por &= ~POE_RW;
> +		new_perms &= ~POE_RW;
>  	if (init_val & PKEY_DISABLE_READ)
> -		new_por &= ~POE_R;
> +		new_perms &= ~POE_R;
>  	if (init_val & PKEY_DISABLE_EXECUTE)
> -		new_por &= ~POE_X;
> +		new_perms &= ~POE_X;
>  
> -	/* Shift the bits in to the correct place in POR for pkey: */
> -	new_por = POR_ELx_PERM_PREP(pkey, new_por);
> -
> -	/* Get old POR and mask off any old bits in place: */
> -	old_por = read_sysreg_s(SYS_POR_EL0);
> -	old_por &= ~(POE_MASK << POR_ELx_PERM_SHIFT(pkey));
> -
> -	/* Write old part along with new part: */
> -	write_sysreg_s(old_por | new_por, SYS_POR_EL0);
> +	por = read_sysreg_s(SYS_POR_EL0);
> +	por = por_elx_set_pkey_perms(por, pkey, new_perms);
> +	write_sysreg_s(por, SYS_POR_EL0);

Was wondering whether to move reading+writing of the register into the same
helper, but you cannot reuse this exactly the same way for SYS_POR_EL1 as it seems.

Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David