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Re: [Xen-devel] [PATCH] openvswitch: Orphan frags before sending to userspace via Netlink to avoid guest stall

On 02/28/2014 08:16 PM, Zoltan Kiss wrote:
The kernel datapath now switched to zerocopy Netlink messages, but that also
means that the pages on frags array are sent straight to userspace. If those
pages came outside the kernel, we have to swap them out with local copies.

Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
  net/openvswitch/datapath.c |    6 ++++++
  1 file changed, 6 insertions(+)

diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index 36f8872..ffb563c 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -464,6 +464,12 @@ static int queue_userspace_packet(struct datapath *dp, 
struct sk_buff *skb,
        nla->nla_len = nla_attr_size(skb->len);

+       if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC))) {
+               err = -ENOMEM;
+               skb_tx_error(skb);
+               goto out;
+       }
        skb_zerocopy(user_skb, skb, skb->len, hlen);

        /* Pad OVS_PACKET_ATTR_PACKET if linear copy was performed */

How about we move the call to skb_orphan_frags() into skb_zerocopy()
itself and call it before we actually reference the frags?

It's not just OVS affected but nfqueue as well.

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