[PATCH rdma-next 1/2] RDMA/core: Prevent rereg_mr for dmabuf umems

The rereg_mr method has always been explicitly blocked in
rdma-core for dmabuf MRs anyway, so add a check to the
ib_umem_check_rereg helper so that each driver doesn't need
to handle it.

Depending on how the driver handled rereg_mr, this also
has the benefit of preventing rereg_mr from being used
to add the IB_ACCESS_MW_BIND flag to a dmabuf MR. This
flag is not allowed during registration, so it seems
sensible to prevent it from being added back with rereg_mr.

Preventing IB_ACCESS_MW_BIND is important for drivers that
support revocable dmabufs and implement "revoke" by issuing
a dereg_mr command to the HW because most(?) HW will reject
this command if the MR has windows bound to it, and a failure
to revoke is supposed to trigger a function reset.

Signed-off-by: Jacob Moroni <[email protected]>
---
 drivers/infiniband/core/umem.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 81f44dadfa52..88110b9661f5 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -677,6 +677,9 @@ int ib_umem_check_rereg(struct ib_umem *umem, int flags, int new_access_flags)
 	if (!umem)
 		return 0;
 
+	if (umem->is_dmabuf)
+		return -EOPNOTSUPP;
+
 	if ((flags & IB_MR_REREG_ACCESS) && !(flags & IB_MR_REREG_TRANS))
 		if (ib_access_writable(new_access_flags) && !umem->writable)
 			return -EACCES;
-- 
2.55.0.229.g6434b31f56-goog