RDMA/efa: Use ib_umem_num_dma_pages()

If ib_umem_find_best_pgsz() returns > PAGE_SIZE then the equation here is
not correct. 'start' should be 'virt'. Change it to use the core code for
page_num and the canonical calculation of page_shift.

Fixes: 40ddb3f0 ("RDMA/efa: Use API to get contiguous memory blocks aligned to device supported page size")
Link: https://lore.kernel.org/r/7-v2-270386b7e60b+28f4-umem_1_jgg@nvidia.comTested-by: Gal Pressman <galpress@amazon.com>
Acked-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/efa/efa_verbs.c

@@ -4,6 +4,7 @@
  */
 
 #include <linux/vmalloc.h>
+#include <linux/log2.h>
 
 #include <rdma/ib_addr.h>
 #include <rdma/ib_umem.h>
@@ -1540,9 +1541,8 @@ struct ib_mr *efa_reg_mr(struct ib_pd *ibpd, u64 start, u64 length,
 		goto err_unmap;
 	}
 
-	params.page_shift = __ffs(pg_sz);
-	params.page_num = DIV_ROUND_UP(length + (start & (pg_sz - 1)),
-				       pg_sz);
+	params.page_shift = order_base_2(pg_sz);
+	params.page_num = ib_umem_num_dma_blocks(mr->umem, pg_sz);
 
 	ibdev_dbg(&dev->ibdev,
 		  "start %#llx length %#llx params.page_shift %u params.page_num %u\n",