io_uring: enable shmem/memfd memory registration

Relax buffer registration restictions, which filters out file backed
memory, and allow shmem/memfd as they have normal anonymous pages
underneath.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -8306,6 +8306,8 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 		for (i = 0; i < nr_pages; i++) {
 			struct vm_area_struct *vma = vmas[i];
 
+			if (vma_is_shmem(vma))
+				continue;
 			if (vma->vm_file &&
 			    !is_file_hugepages(vma->vm_file)) {
 				ret = -EOPNOTSUPP;