On Tue, Aug 20, 2024 at 03:19:13PM +0800, Xuan Zhuo 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.
>
> 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;
