On Tue, Oct 29, 2024 at 4:47 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> When the frag just got a page, then may lead to regression on VM.
> Specially if the sysctl net.core.high_order_alloc_disable value is 1,
> then the frag always get a page when do refill.
>
> 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.
>
> The commit f9dac92ba908 ("virtio_ring: enable premapped mode whatever
> use_dma_api") introduced this problem. And we reverted some commits to
> fix this in last linux version. Now we try to enable it and fix this
> bug directly.
>
> Here, when the frag size is not enough, we reduce the buffer len to fix
> this problem.
>
> Reported-by: "Si-Wei Liu" <si-wei.liu@xxxxxxxxxx>
> Tested-by: Darren Kenny <darren.kenny@xxxxxxxxxx>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Thanks
