On Thu, Mar 21, 2024 at 06:07:55PM -0400, peterx@xxxxxxxxxx wrote:
> From: Peter Xu <peterx@xxxxxxxxxx>
>
> Hugepd format for GUP is only used in PowerPC with hugetlbfs. There are
> some kernel usage of hugepd (can refer to hugepd_populate_kernel() for
> PPC_8XX), however those pages are not candidates for GUP.
>
> Commit a6e79df92e4a ("mm/gup: disallow FOLL_LONGTERM GUP-fast writing to
> file-backed mappings") added a check to fail gup-fast if there's potential
> risk of violating GUP over writeback file systems. That should never apply
> to hugepd. Considering that hugepd is an old format (and even
> software-only), there's no plan to extend hugepd into other file typed
> memories that is prone to the same issue.
>
> Drop that check, not only because it'll never be true for hugepd per any
> known plan, but also it paves way for reusing the function outside
> fast-gup.
>
> To make sure we'll still remember this issue just in case hugepd will be
> extended to support non-hugetlbfs memories, add a rich comment above
> gup_huge_pd(), explaining the issue with proper references.
>
> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
> mm/gup.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Jason
