Re: [PATCH 1/2] mm: Allow arch code to control the user page table ceiling

[Hugh Dickins <hughd@google.com>]

On Mon, 18 Feb 2013, Catalin Marinas wrote:

> From: Hugh Dickins <hughd@google.com>

You're being generous to me :)
Thanks for doing most of the work, yes, this looks fine.
BUt I'd have expected a Cc stable below: see comment on 2/2.

Hugh

> 
> On architectures where a pgd entry may be shared between user and kernel
> (ARM+LPAE), freeing page tables needs a ceiling other than 0. This patch
> introduces a generic USER_PGTABLES_CEILING that arch code can override.
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>
> [catalin.marinas@arm.com: commit log; shift_arg_pages(), asm-generic/pgtables.h changes]
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>  fs/exec.c                     |  4 ++--
>  include/asm-generic/pgtable.h | 10 ++++++++++
>  mm/mmap.c                     |  4 ++--
>  3 files changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index 20df02c..547eaaa 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -613,7 +613,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
>  		 * when the old and new regions overlap clear from new_end.
>  		 */
>  		free_pgd_range(&tlb, new_end, old_end, new_end,
> -			vma->vm_next ? vma->vm_next->vm_start : 0);
> +			vma->vm_next ? vma->vm_next->vm_start : USER_PGTABLES_CEILING);
>  	} else {
>  		/*
>  		 * otherwise, clean from old_start; this is done to not touch
> @@ -622,7 +622,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
>  		 * for the others its just a little faster.
>  		 */
>  		free_pgd_range(&tlb, old_start, old_end, new_end,
> -			vma->vm_next ? vma->vm_next->vm_start : 0);
> +			vma->vm_next ? vma->vm_next->vm_start : USER_PGTABLES_CEILING);
>  	}
>  	tlb_finish_mmu(&tlb, new_end, old_end);
>  
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 5cf680a..f50a87d 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -7,6 +7,16 @@
>  #include <linux/mm_types.h>
>  #include <linux/bug.h>
>  
> +/*
> + * On almost all architectures and configurations, 0 can be used as the
> + * upper ceiling to free_pgtables(): on many architectures it has the same
> + * effect as using TASK_SIZE.  However, there is one configuration which
> + * must impose a more careful limit, to avoid freeing kernel pgtables.
> + */
> +#ifndef USER_PGTABLES_CEILING
> +#define USER_PGTABLES_CEILING	0UL
> +#endif
> +
>  #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
>  extern int ptep_set_access_flags(struct vm_area_struct *vma,
>  				 unsigned long address, pte_t *ptep,
> diff --git a/mm/mmap.c b/mm/mmap.c
> index d1e4124..e262710 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2262,7 +2262,7 @@ static void unmap_region(struct mm_struct *mm,
>  	update_hiwater_rss(mm);
>  	unmap_vmas(&tlb, vma, start, end);
>  	free_pgtables(&tlb, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
> -				 next ? next->vm_start : 0);
> +				 next ? next->vm_start : USER_PGTABLES_CEILING);
>  	tlb_finish_mmu(&tlb, start, end);
>  }
>  
> @@ -2640,7 +2640,7 @@ void exit_mmap(struct mm_struct *mm)
>  	/* Use -1 here to ensure all VMAs in the mm are unmapped */
>  	unmap_vmas(&tlb, vma, 0, -1);
>  
> -	free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
> +	free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
>  	tlb_finish_mmu(&tlb, 0, -1);
>  
>  	/*
>