IB/mlx5: Add mmap support for VAR

Add mmap support for VAR, it uses the 'offset' command mode with
involvement of IB core APIs to find the previously allocated mmap entry.

Link: https://lore.kernel.org/r/20191212110928.334995-6-leon@kernel.org
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mlx5/main.c

@@ -2253,7 +2253,10 @@ static int mlx5_ib_mmap_offset(struct mlx5_ib_dev *dev,
 
 	mentry = to_mmmap(entry);
 	pfn = (mentry->address >> PAGE_SHIFT);
-	prot = pgprot_writecombine(vma->vm_page_prot);
+	if (mentry->mmap_flag == MLX5_IB_MMAP_TYPE_VAR)
+		prot = pgprot_noncached(vma->vm_page_prot);
+	else
+		prot = pgprot_writecombine(vma->vm_page_prot);
 	ret = rdma_user_mmap_io(ucontext, vma, pfn,
 				entry->npages * PAGE_SIZE,
 				prot,