Re: [PATCH] udmabuf: revert 'Add support for mapping hugepages (v4)'

[Gerd Hoffmann]

On Thu, Jun 08, 2023 at 01:49:27PM -0700, Mike Kravetz wrote:
> This effectively reverts commit 16c243e99d33 ("udmabuf: Add support
> for mapping hugepages (v4)").  Recently, Junxiao Chang found a BUG
> with page map counting as described here [1].  This issue pointed out
> that the udmabuf driver was making direct use of subpages of hugetlb
> pages.  This is not a good idea, and no other mm code attempts such use.
> In addition to the mapcount issue, this also causes issues with hugetlb
> vmemmap optimization and page poisoning.
> 
> For now, remove hugetlb support.
> 
> If udmabuf wants to be used on hugetlb mappings, it should be changed to
> only use complete hugetlb pages.  This will require different alignment
> and size requirements on the UDMABUF_CREATE API.
> 
> [1] 
> https://lore.kernel.org/linux-mm/20230512072036.1027784-1-junxiao.chang@intel.com/
> 
> Fixes: 16c243e99d33 ("udmabuf: Add support for mapping hugepages (v4)")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Acked-by: Gerd Hoffmann <kraxel@redhat.com>