Re: [PATCH rdma-next] RDMA/mlx5: Set mkeys for dmabuf at PAGE_SIZE

[Leon Romanovsky <leon@kernel.org>]

On Mon, Jun 17, 2024 at 10:59:05AM -0300, Jason Gunthorpe wrote:
> On Thu, Jun 13, 2024 at 09:01:42PM +0300, Leon Romanovsky wrote:
> > From: Chiara Meiohas <cmeiohas@nvidia.com>
> > 
> > Set the mkey for dmabuf at PAGE_SIZE to support any SGL
> > after a move operation.
> > 
> > ib_umem_find_best_pgsz returns 0 on error, so it is
> > incorrect to check the returned page_size against PAGE_SIZE
> 
> This commit message is not clear enough for something that need to be
> backported:

This patch is going to be backported without any relation to the commit
message as it has Fixes line.

Thanks

> 
> RDMA/mlx5: Support non-page size aligned DMABUF mkeys
> 
> The mkey page size for DMABUF is fixed at PAGE_SIZE because we have to
> support a move operation that could change a large-sized page list
> into a small page-list and the mkey must be able to represent it.
> 
> The test for this is not quite correct, instead of checking the output
> of mlx5_umem_find_best_pgsz() the call to ib_umem_find_best_pgsz
> should specify the exact HW/SW restriction - only PAGE_SIZE is
> accepted.
> 
> Then the normal logic for dealing with leading/trailing sub page
> alignment works correctly and sub page size DMBUF mappings can be
> supported.
> 
> This is particularly painful on 64K kernels.

Unfortunately, the patch was already merged, so I can't change the
commit message in for-next branch.

Thanks

> 
> Jason