[PATCH v1 08/12] mm/rmap: handle device-exclusive entries correctly in try_to_unmap_one()

[David Hildenbrand]

On 30.01.25 11:10, Simona Vetter wrote:
> On Wed, Jan 29, 2025 at 12:54:06PM +0100, David Hildenbrand wrote:
>> Ever since commit b756a3b5e7ea ("mm: device exclusive memory access")
>> we can return with a device-exclusive entry from page_vma_mapped_walk().
>>
>> try_to_unmap_one() is not prepared for that, so teach it about these
>> non-present nonswap PTEs.
>>
>> Before that, could we also have triggered this case with device-private
>> entries? Unlikely.
> 
> Just quick comment on this, I'm still pondering all the other aspects.
> 
> device-private memory is entirely owned by the driver, the core mm isn't
> supposed to touch these beyond migrating it back to system memory in
> do_swap_page. Plus using rmap when the driver asks for invalidating
> mappings as needed.
> 
> So no lru, thp, migration or anything initiated by core mm should ever
> happen on these device private pages. If it does, it'd be a bug.

I was not 100% sure about HWPoison handling, that's why I added that 
comment. In other regards I agree: reclaim etc. does not apply.

-- 
Cheers,

David / dhildenb