Re: [PATCH 1/2] mm/hmm: hmm_range_fault() NULL pointer bug

From: Ralph Campbell
Date: Mon Aug 26 2019 - 14:02:15 EST

On 8/24/19 3:37 PM, Christoph Hellwig wrote:
On Fri, Aug 23, 2019 at 03:17:52PM -0700, Ralph Campbell wrote:
Although hmm_range_fault() calls find_vma() to make sure that a vma exists
before calling walk_page_range(), hmm_vma_walk_hole() can still be called
with walk->vma == NULL if the start and end address are not contained
within the vma range.

Should we convert to walk_vma_range instead? Or keep walk_page_range
but drop searching the vma ourselves?

Except for that the patch looks good to me:

Reviewed-by: Christoph Hellwig <hch@xxxxxx>

I think keeping the call to walk_page_range() makes sense.
Jason is hoping to be able to snapshot a range with & without vmas
and have the pfns[] filled with empty/valid entries as appropriate.

I plan to repost my patch changing hmm_range_fault() to use
walk.test_walk which will remove the call to find_vma().
Jason had some concerns about testing it so that's why I have
been working on some HMM self tests before resending it.