RDMA/umem: Introduce an option to revoke DMABUF umem

Introduce an option to revoke DMABUF umem.

This option will retain the umem allocation while revoking its DMA
mapping. Furthermore, any subsequent attempts to map the pages should
fail once the umem has been revoked.

This functionality will be utilized in the upcoming patches in the
series, where we aim to delay umem deallocation until the mkey
deregistration. However, we must unmap its pages immediately.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://patch.msgid.link/a38270f2fe4a194868ca2312f4c1c760e51bcbff.1722512548.git.leon@kernel.org


Signed-off-by: Leon Romanovsky <leon@kernel.org>