virtio-net: restrict build_skb() use to some arches
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: fb32856b ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Guenter Roeck <linux@roeck-us.net> Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com> Cc: Jason Wang <jasowang@redhat.com> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: virtualization@lists.linux-foundation.org Signed-off-by: David S. Miller <davem@davemloft.net>
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