Re: [PATCH 2/6] s390/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

[Christophe Leroy]

Le 03/06/2022 à 12:14, Anshuman Khandual a écrit :
> This defines and exports a platform specific custom vm_get_page_prot() via
> subscribing ARCH_HAS_VM_GET_PAGE_PROT. Subsequently all __SXXX and __PXXX
> macros can be dropped which are no longer needed.
> 
> Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
> Cc: linux-s390@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Acked-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
> Acked-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
>   arch/s390/Kconfig               |  1 +
>   arch/s390/include/asm/pgtable.h | 17 -----------------
>   arch/s390/mm/mmap.c             | 33 +++++++++++++++++++++++++++++++++
>   3 files changed, 34 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index b17239ae7bd4..cdcf678deab1 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -81,6 +81,7 @@ config S390
>   	select ARCH_HAS_SYSCALL_WRAPPER
>   	select ARCH_HAS_UBSAN_SANITIZE_ALL
>   	select ARCH_HAS_VDSO_DATA
> +	select ARCH_HAS_VM_GET_PAGE_PROT
>   	select ARCH_HAVE_NMI_SAFE_CMPXCHG
>   	select ARCH_INLINE_READ_LOCK
>   	select ARCH_INLINE_READ_LOCK_BH
> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> index a397b072a580..c63a05b5368a 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -424,23 +424,6 @@ static inline int is_module_addr(void *addr)
>    * implies read permission.
>    */
>            /*xwr*/
> -#define __P000	PAGE_NONE
> -#define __P001	PAGE_RO
> -#define __P010	PAGE_RO
> -#define __P011	PAGE_RO
> -#define __P100	PAGE_RX
> -#define __P101	PAGE_RX
> -#define __P110	PAGE_RX
> -#define __P111	PAGE_RX
> -
> -#define __S000	PAGE_NONE
> -#define __S001	PAGE_RO
> -#define __S010	PAGE_RW
> -#define __S011	PAGE_RW
> -#define __S100	PAGE_RX
> -#define __S101	PAGE_RX
> -#define __S110	PAGE_RWX
> -#define __S111	PAGE_RWX
>   
>   /*
>    * Segment entry (large page) protection definitions.
> diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
> index d545f5c39f7e..11d75b8d5ec0 100644
> --- a/arch/s390/mm/mmap.c
> +++ b/arch/s390/mm/mmap.c
> @@ -188,3 +188,36 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
>   		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
>   	}
>   }
> +
> +pgprot_t vm_get_page_prot(unsigned long vm_flags)
> +{
> +	switch (vm_flags & (VM_READ | VM_WRITE | VM_EXEC | VM_SHARED)) {
> +	case VM_NONE:
> +		return PAGE_NONE;
> +	case VM_READ:
> +	case VM_WRITE:
> +	case VM_WRITE | VM_READ:
> +		return PAGE_RO;
> +	case VM_EXEC:
> +	case VM_EXEC | VM_READ:
> +	case VM_EXEC | VM_WRITE:
> +	case VM_EXEC | VM_WRITE | VM_READ:
> +		return PAGE_RX;
> +	case VM_SHARED:
> +		return PAGE_NONE;
> +	case VM_SHARED | VM_READ:
> +		return PAGE_RO;
> +	case VM_SHARED | VM_WRITE:
> +	case VM_SHARED | VM_WRITE | VM_READ:
> +		return PAGE_RW;
> +	case VM_SHARED | VM_EXEC:
> +	case VM_SHARED | VM_EXEC | VM_READ:
> +		return PAGE_RX;
> +	case VM_SHARED | VM_EXEC | VM_WRITE:
> +	case VM_SHARED | VM_EXEC | VM_WRITE | VM_READ:
> +		return PAGE_RWX;
> +	default:
> +		BUILD_BUG();
> +	}
> +}
> +EXPORT_SYMBOL(vm_get_page_prot);

Wasn't it demonstrated in previous discussions that a switch/case is 
suboptimal compared to a table cell read ?

In order to get rid of the _Sxxx/_Pxxx macros, my preference would go to 
having architectures provide their own protection_map[] table, and keep 
the generic vm_get_page_prot() for the architectures would don't need a 
specific version of it.

This comment applies to all following patches as well.