Virtualization - Apr 2021 - [PATCH net-next] virtio-net: restrict build_skb() use to some arches

On Tue, Apr 20, 2021 at 01:01:44PM -0700, Eric Dumazet
wrote:
> From: Eric Dumazet <edumazet at google.com>
> 
> build_skb() is supposed to be followed by
> skb_reserve(skb, NET_IP_ALIGN), so that IP headers are word-aligned.
> (Best practice is to reserve NET_IP_ALIGN+NET_SKB_PAD, but the NET_SKB_PAD
> part is only a performance optimization if tunnel encaps are added.)
> 
> Unfortunately virtio_net has not provisioned this reserve.
> We can only use build_skb() for arches where NET_IP_ALIGN == 0
> 
> We might refine this later, with enough testing.
> 
> Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when
there's sufficient tailroom")
> Signed-off-by: Eric Dumazet <edumazet at google.com>
> Reported-by: Guenter Roeck <linux at roeck-us.net>
> Cc: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> Cc: Jason Wang <jasowang at redhat.com>
> Cc: "Michael S. Tsirkin" <mst at redhat.com>
> Cc: virtualization at lists.linux-foundation.org
Tested-by: Guenter Roeck <linux at roeck-us.net>

on alpha, sh4 (little endian).

Thanks!

Guenter