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

Christophe Leroy
2022-06-03T12:25:14Z

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@linux.ibm.com>
> Cc: Vasily Gorbik <gor@linux.ibm.com>
> Cc: linux-s390@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Acked-by: Sven Schnelle <svens@linux.ibm.com>
> Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> 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.