vfio/mlx5: Fix an unwind issue in mlx5vf_add_migration_pages()

Fix an unwind issue in mlx5vf_add_migration_pages().

If a set of pages is allocated but fails to be added to the SG table,
they need to be freed to prevent a memory leak.

Any pages successfully added to the SG table will be freed as part of
mlx5vf_free_data_buffer().

Fixes: 6fadb02 ("vfio/mlx5: Implement vfio_pci driver for mlx5 devices")
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20241114095318.16556-2-yishaih@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/mlx5/cmd.c

@@ -423,6 +423,7 @@ static int mlx5vf_add_migration_pages(struct mlx5_vhca_data_buffer *buf,
 	unsigned long filled;
 	unsigned int to_fill;
 	int ret;
+	int i;
 
 	to_fill = min_t(unsigned int, npages, PAGE_SIZE / sizeof(*page_list));
 	page_list = kvzalloc(to_fill * sizeof(*page_list), GFP_KERNEL_ACCOUNT);
@@ -443,7 +444,7 @@ static int mlx5vf_add_migration_pages(struct mlx5_vhca_data_buffer *buf,
 			GFP_KERNEL_ACCOUNT);
 
 		if (ret)
-			goto err;
+			goto err_append;
 		buf->allocated_length += filled * PAGE_SIZE;
 		/* clean input for another bulk allocation */
 		memset(page_list, 0, filled * sizeof(*page_list));
@@ -454,6 +455,9 @@ static int mlx5vf_add_migration_pages(struct mlx5_vhca_data_buffer *buf,
 	kvfree(page_list);
 	return 0;
 
+err_append:
+	for (i = filled - 1; i >= 0; i--)
+		__free_page(page_list[i]);
 err:
 	kvfree(page_list);
 	return ret;