[PATCH] mm/migrate_device: Return number of migrating pages in args->cpages

[Alistair Popple]

Hi Andrew,

I realize it's getting late in the cycle but any chance you could take
this one as well for v6.1-rc6? It fixes a minor bug introduced in
v6.1-rc1 which could cause some drivers to think they can't migrate
pages when they can. Thanks.

Ralph Campbell <rcampbell at nvidia.com> writes:

> On 11/10/22 16:51, Alistair Popple wrote:
>> migrate_vma->cpages originally contained a count of the number of
>> pages migrating including non-present pages which can be poluated
>
> "populated"
>
>> directly on the target.
>>
>> Commit 241f68859656 ("mm/migrate_device.c: refactor migrate_vma and
>> migrate_deivce_coherent_page()") inadvertantly changed this to contain
>> just the number of pages that were unmapped. Usage of
>> migrate_vma->cpages isn't documented, but most drivers use it to see
>> if all the requested addresses can be migrated so restore the original
>> behaviour.
>>
>> Fixes: 241f68859656 ("mm/migrate_device.c: refactor migrate_vma and migrate_deivce_coherent_page()")
>> Signed-off-by: Alistair Popple <apopple at nvidia.com>
>> Reported-by: Ralph Campbell <rcampbell at nvidia.com>
>
> You can add
> Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
>
> Thanks!