Re: [PATCH V4 2/7] powerpc/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

[Christophe Leroy]

Le 07/04/2022 à 12:32, Anshuman Khandual a écrit :
> This defines and exports a platform specific custom vm_get_page_prot() via
> subscribing ARCH_HAS_VM_GET_PAGE_PROT. While here, this also localizes
> arch_vm_get_page_prot() as powerpc_vm_get_page_prot() and moves it near
> vm_get_page_prot().
> 
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
>   arch/powerpc/Kconfig            |  1 +
>   arch/powerpc/include/asm/mman.h | 12 ------------
>   arch/powerpc/mm/mmap.c          | 26 ++++++++++++++++++++++++++
>   3 files changed, 27 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 174edabb74fa..eb9b6ddbf92f 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -140,6 +140,7 @@ config PPC
>   	select ARCH_HAS_TICK_BROADCAST		if GENERIC_CLOCKEVENTS_BROADCAST
>   	select ARCH_HAS_UACCESS_FLUSHCACHE
>   	select ARCH_HAS_UBSAN_SANITIZE_ALL
> +	select ARCH_HAS_VM_GET_PAGE_PROT
>   	select ARCH_HAVE_NMI_SAFE_CMPXCHG
>   	select ARCH_KEEP_MEMBLOCK
>   	select ARCH_MIGHT_HAVE_PC_PARPORT
> diff --git a/arch/powerpc/include/asm/mman.h b/arch/powerpc/include/asm/mman.h
> index 7cb6d18f5cd6..1b024e64c8ec 100644
> --- a/arch/powerpc/include/asm/mman.h
> +++ b/arch/powerpc/include/asm/mman.h
> @@ -24,18 +24,6 @@ static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
>   }
>   #define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
>   
> -static inline pgprot_t arch_vm_get_page_prot(unsigned long vm_flags)
> -{
> -#ifdef CONFIG_PPC_MEM_KEYS
> -	return (vm_flags & VM_SAO) ?
> -		__pgprot(_PAGE_SAO | vmflag_to_pte_pkey_bits(vm_flags)) :
> -		__pgprot(0 | vmflag_to_pte_pkey_bits(vm_flags));
> -#else
> -	return (vm_flags & VM_SAO) ? __pgprot(_PAGE_SAO) : __pgprot(0);
> -#endif
> -}
> -#define arch_vm_get_page_prot(vm_flags) arch_vm_get_page_prot(vm_flags)
> -
>   static inline bool arch_validate_prot(unsigned long prot, unsigned long addr)
>   {
>   	if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | PROT_SAO))
> diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
> index c475cf810aa8..cd17bd6fa36b 100644
> --- a/arch/powerpc/mm/mmap.c
> +++ b/arch/powerpc/mm/mmap.c
> @@ -254,3 +254,29 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
>   		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
>   	}
>   }
> +
> +#ifdef CONFIG_PPC64
> +static pgprot_t powerpc_vm_get_page_prot(unsigned long vm_flags)
> +{
> +#ifdef CONFIG_PPC_MEM_KEYS
> +	return (vm_flags & VM_SAO) ?
> +		__pgprot(_PAGE_SAO | vmflag_to_pte_pkey_bits(vm_flags)) :
> +		__pgprot(0 | vmflag_to_pte_pkey_bits(vm_flags));
> +#else
> +	return (vm_flags & VM_SAO) ? __pgprot(_PAGE_SAO) : __pgprot(0);
> +#endif
> +}
> +#else
> +static pgprot_t powerpc_vm_get_page_prot(unsigned long vm_flags)
> +{
> +	return __pgprot(0);
> +}
> +#endif /* CONFIG_PPC64 */

Can we reduce this forest of #ifdefs and make it more readable ?

mm/mmap.c is going away with patch 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/d6d849621f821af253e777a24eda4c648814a76e.1646847562.git.christophe.leroy@xxxxxxxxxx/

So it would be better to add two versions of vm_get_page_prot(), for 
instance one in mm/pgtable_64.c and one in mm/pgtable_32.c


> +
> +pgprot_t vm_get_page_prot(unsigned long vm_flags)
> +{
> +	return __pgprot(pgprot_val(protection_map[vm_flags &
> +			(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
> +	       pgprot_val(powerpc_vm_get_page_prot(vm_flags)));
> +}
> +EXPORT_SYMBOL(vm_get_page_prot);

By the way I'm a bit puzzled with the name powerpc_vm_get_page_prot(), 
the name suggests that it's just a powerpc replacement of 
vm_get_page_prot(). I'd prefer if it was named __vm_get_page_prot(), it 
would be clearer that it is a complement to vm_get_page_prot() and not a 
remplacement.

Christophe