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

[Leon Romanovsky <leon@kernel.org>]

On Tue, Jun 18, 2024 at 10:02:33AM -0300, Jason Gunthorpe wrote:
> On Tue, Jun 18, 2024 at 03:08:14PM +0300, Leon Romanovsky wrote:
> > > > 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.
> 
> People doing backports complain with some regularity about poor commit
> messages, especailly now that so many patches get a CVE. We need to do
> better.

It is always true.

> 
> > > 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.
> 
> How is it already merged? There was no message from your script - are
> you loosing emails??

In this specific case, no.
I switched too early from branch and my thank-you message (b4 ty ..)
simply wasn't sent.

Thanks

> 
> Jason