Re: [PATCH V5 02/26] mm/mmap: Define DECLARE_VM_GET_PAGE_PROT

[Christophe Leroy]

Le 27/06/2022 à 06:58, Anshuman Khandual a écrit :
> This just converts the generic vm_get_page_prot() implementation into a new
> macro i.e DECLARE_VM_GET_PAGE_PROT which later can be used across platforms
> when enabling them with ARCH_HAS_VM_GET_PAGE_PROT. This does not create any
> functional change.
> 
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>

Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>

> ---
>   include/linux/pgtable.h | 28 ++++++++++++++++++++++++++++
>   mm/mmap.c               | 26 +-------------------------
>   2 files changed, 29 insertions(+), 25 deletions(-)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 3cdc16cfd867..014ee8f0fbaa 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1689,4 +1689,32 @@ typedef unsigned int pgtbl_mod_mask;
>   #define MAX_PTRS_PER_P4D PTRS_PER_P4D
>   #endif
>   
> +/* description of effects of mapping type and prot in current implementation.
> + * this is due to the limited x86 page protection hardware.  The expected
> + * behavior is in parens:
> + *
> + * map_type	prot
> + *		PROT_NONE	PROT_READ	PROT_WRITE	PROT_EXEC
> + * MAP_SHARED	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
> + *		w: (no) no	w: (no) no	w: (yes) yes	w: (no) no
> + *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
> + *
> + * MAP_PRIVATE	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
> + *		w: (no) no	w: (no) no	w: (copy) copy	w: (no) no
> + *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
> + *
> + * On arm64, PROT_EXEC has the following behaviour for both MAP_SHARED and
> + * MAP_PRIVATE (with Enhanced PAN supported):
> + *								r: (no) no
> + *								w: (no) no
> + *								x: (yes) yes
> + */
> +#define DECLARE_VM_GET_PAGE_PROT					\
> +pgprot_t vm_get_page_prot(unsigned long vm_flags)			\
> +{									\
> +		return protection_map[vm_flags &			\
> +			(VM_READ | VM_WRITE | VM_EXEC | VM_SHARED)];	\
> +}									\
> +EXPORT_SYMBOL(vm_get_page_prot);
> +
>   #endif /* _LINUX_PGTABLE_H */
> diff --git a/mm/mmap.c b/mm/mmap.c
> index b01f0280bda2..b46d5e931bb3 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -81,26 +81,6 @@ static void unmap_region(struct mm_struct *mm,
>   		struct vm_area_struct *vma, struct vm_area_struct *prev,
>   		unsigned long start, unsigned long end);
>   
> -/* description of effects of mapping type and prot in current implementation.
> - * this is due to the limited x86 page protection hardware.  The expected
> - * behavior is in parens:
> - *
> - * map_type	prot
> - *		PROT_NONE	PROT_READ	PROT_WRITE	PROT_EXEC
> - * MAP_SHARED	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
> - *		w: (no) no	w: (no) no	w: (yes) yes	w: (no) no
> - *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
> - *
> - * MAP_PRIVATE	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
> - *		w: (no) no	w: (no) no	w: (copy) copy	w: (no) no
> - *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
> - *
> - * On arm64, PROT_EXEC has the following behaviour for both MAP_SHARED and
> - * MAP_PRIVATE (with Enhanced PAN supported):
> - *								r: (no) no
> - *								w: (no) no
> - *								x: (yes) yes
> - */
>   #ifdef __P000
>   pgprot_t protection_map[16] __ro_after_init = {
>   	[VM_NONE]					= __P000,
> @@ -123,11 +103,7 @@ pgprot_t protection_map[16] __ro_after_init = {
>   #endif
>   
>   #ifndef CONFIG_ARCH_HAS_VM_GET_PAGE_PROT
> -pgprot_t vm_get_page_prot(unsigned long vm_flags)
> -{
> -	return protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
> -}
> -EXPORT_SYMBOL(vm_get_page_prot);
> +DECLARE_VM_GET_PAGE_PROT
>   #endif	/* CONFIG_ARCH_HAS_VM_GET_PAGE_PROT */
>   
>   static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)