[ovs-dev] [PATCH] openvswitch: Orphan frags before sending to userspace via Netlink to avoid guest stall

[Zoltan Kiss]

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 at citrix.com>
---
 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 */