On Tue, Aug 20, 2024 at 3:19 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> leads to regression on VM with the sysctl value of:
>
> - net.core.high_order_alloc_disable=1
>
> which could see reliable crashes or scp failure (scp a file 100M in size
> to VM):
>
> The issue is that the virtnet_rq_dma takes up 16 bytes at the beginning
> of a new frag. When the frag size is larger than PAGE_SIZE,
> everything is fine. However, if the frag is only one page and the
> total size of the buffer and virtnet_rq_dma is larger than one page, an
> overflow may occur. In this case, if an overflow is possible, I adjust
> the buffer size. If net.core.high_order_alloc_disable=1, the maximum
> buffer size is 4096 - 16. If net.core.high_order_alloc_disable=0, only
> the first buffer of the frag is affected.
I wonder instead of trying to make use of headroom, would it be
simpler if we allocate dedicated arrays of virtnet_rq_dma？
Btw, I see it has a need_sync, I wonder if it can help for performance
or not? If not, any reason to keep that?
>
> Fixes: f9dac92ba908 ("virtio_ring: enable premapped mode whatever use_dma_api")
> Reported-by: "Si-Wei Liu" <si-wei.liu@xxxxxxxxxx>
> Closes: http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@xxxxxxxxxx
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c6af18948092..e5286a6da863 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -918,9 +918,6 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
> void *buf, *head;
> dma_addr_t addr;
>
> - if (unlikely(!skb_page_frag_refill(size, alloc_frag, gfp)))
> - return NULL;
> -
> head = page_address(alloc_frag->page);
>
> dma = head;
> @@ -2421,6 +2418,9 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> len = SKB_DATA_ALIGN(len) +
> SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>
> + if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
> + return -ENOMEM;
> +
> buf = virtnet_rq_alloc(rq, len, gfp);
> if (unlikely(!buf))
> return -ENOMEM;
> @@ -2521,6 +2521,12 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> */
> len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
>
> + if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> + return -ENOMEM;
> +
> + if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
> + len -= sizeof(struct virtnet_rq_dma);
> +
> buf = virtnet_rq_alloc(rq, len + room, gfp);
> if (unlikely(!buf))
> return -ENOMEM;
> --
> 2.32.0.3.g01195cf9f
Thanks
>
