Re: [PATCH] mm: nommu: fix remap_pfn_range()

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 27 May 2011 11:50:03 +0800
Bob Liu <lliubbo@gmail.com> wrote:

> remap_pfn_range() does not update vma->end on no mmu arch which will
> cause munmap() fail because it can't match the vma.
> 
> eg. fb_mmap() in fbmem.c will call io_remap_pfn_range() which is
> remap_pfn_range() on nommu arch, if an address is not page aligned vma->start
> will be changed in remap_pfn_range(), but neither size nor vma->end will be
> updated. Then munmap(start, len) can't find the vma to free, because it need to
> compare (start + len) with vma->end.
> 
> Signed-off-by: Bob Liu <lliubbo@gmail.com>
> ---
>  mm/nommu.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 1fd0c51..829848a 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -1817,6 +1817,7 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long from,
>  		unsigned long to, unsigned long size, pgprot_t prot)
>  {
>  	vma->vm_start = vma->vm_pgoff << PAGE_SHIFT;
> +	vma->vm_end = vma->vm_start + size;
>  	return 0;
>  }
>  EXPORT_SYMBOL(remap_pfn_range);

hm.

The MMU version of remap_pfn_range() doesn't do this.  Seems that it
just leaves the omitted parts of the vma unmapped.  Obviously nommu
can't do that, but the divergence is always a concern.

Thsi implementation could lead to overlapping vmas.  Should we be
checking that it fits?




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