Re: [PATCH] Handle vma regions with no backing page

[Anthony Liguori <aliguori@us.ibm.com>]

Andrea Arcangeli wrote:
> On Tue, Apr 29, 2008 at 09:32:09AM -0500, Anthony Liguori wrote:
>   
>> +		vma = find_vma(current->mm, addr);
>> +		if (vma == NULL) {
>> +			get_page(bad_page);
>> +			return page_to_pfn(bad_page);
>> +		}
>>     
>
> Here you must check vm_start address, find_vma only checks addr <
> vm_end but there's no guarantee addr >= vm_start yet.
>   

Indeed.

>> +
>> +		BUG_ON(!(vma->vm_flags & VM_IO));
>>     
>
> For consistency we should return bad_page and not bug on, VM_IO and
> VM_PFNMAP can theoretically not be set at the same time, otherwise
> get_user_pages would be buggy checking against VM_PFNMAP|VM_IO. I
> doubt anybody isn't setting VM_IO before calling remap_pfn_range but
> anyway...
>
> Secondly the really correct check is against VM_PFNMAP. This is
> because PFNMAP is set at the same time of vm_pgoff = pfn. VM_IO is not
> even if in theory if a driver uses ->fault instead of remap_pfn_range,
> shouldn't set VM_IO and it should only set VM_RESERVED. VM_IO is about
> keeping gdb/coredump out as they could mess with the hardware if they
> read, PFNMAP is about remap_pfn_range having been called and pgoff
> pointing to the first pfn mapped at vm_start address.
>   

Good point.  I've updated the patch.  Will send out again once I've 
gotten to test it.

Regards,

Anthony Liguori

> Patch is in the right direction, way to go!
>   


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