Re: [PATCH 02/21] arm64/iommu: improve mmap bounds checking

[Christoph Hellwig]

On Fri, Apr 05, 2019 at 06:30:52PM +0100, Robin Murphy wrote:
> On 27/03/2019 08:04, Christoph Hellwig wrote:
>> The nr_pages checks should be done for all mmap requests, not just those
>> using remap_pfn_range.
>
> Hmm, the logic in iommu_dma_mmap() inherently returns an error for the "off 
> >= nr_pages" case already. It's also supposed to be robust against the 
> "vma_pages(vma) > nr_pages - off" condition, although by making the partial 
> mapping and treating it as a success, rather than doing nothing and 
> returning an error. What's the exact motivation here?

Have one error check at the front of the function that is identical
to the mmap checks in the other dma_map_ops instances so that:

 a) we get the same error behavior for partial requests everywhere
 b) we can lift these checks into common code in the next round.