Re: [V9fs-developer] [PATCH] net/9p: avoid request size exceed to the virtqueue number in the zero copy

piaojun
2018-08-06T08:33:52Z

Hi Yiwen,

On 2018/8/3 14:50, jiangyiwen wrote:
> Unfortunately, when the address(input and response headers) are not
> at page boundary, it will need two extra entry in the zero copy, or
> else it will cause sg array out of bounds.
>
> To avoid the problem, we should subtract two pages for maxsize.
>
> Signed-off-by: Yiwen Jiang <jiangyiwen@huawei.com>
> ---
> net/9p/trans_virtio.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index 6265d1d..63591b2 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -754,11 +754,12 @@ static void p9_virtio_remove(struct virtio_device *vdev)
> .cancel = p9_virtio_cancel,
> /*
> * We leave one entry for input and one entry for response
> - * headers. We also skip one more entry to accomodate, address
> - * that are not at page boundary, that can result in an extra
> - * page in zero copy.
> + * headers. We also skip three more entrys to accomodate
> + * (input + response headers + data pages), address
> + * that are not at page boundary, that can result in
> + * an extra page in zero copy.

Here should be two extra pages.

Thanks,
Jun

> */
> - .maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 3),
> + .maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 5),
> .def = 1,
> .owner = THIS_MODULE,
> };
>