Re: [PATCH mm-unstable v1 10/20] RDMA/umem: remove FOLL_FORCE usage

Jason Gunthorpe
2022-11-17T00:46:58Z

On Wed, Nov 16, 2022 at 11:26:49AM +0100, David Hildenbrand wrote:
> GUP now supports reliable R/O long-term pinning in COW mappings, such
> that we break COW early. MAP_SHARED VMAs only use the shared zeropage so
> far in one corner case (DAXFS file with holes), which can be ignored
> because GUP does not support long-term pinning in fsdax (see
> check_vma_flags()).
>
> Consequently, FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM is no longer required
> for reliable R/O long-term pinning: FOLL_LONGTERM is sufficient. So stop
> using FOLL_FORCE, which is really only for ptrace access.
>
> Tested-by: Leon Romanovsky <leonro@nvidia.com> # Over mlx4 and mlx5.
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Leon Romanovsky <leon@kernel.org>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> drivers/infiniband/core/umem.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason