[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] openvswitch: Orphan frags before sending to userspace via Netlink to avoid guest stall
On 07/03/14 04:46, Pravin Shelar wrote: On Thu, Mar 6, 2014 at 9:09 AM, Zoltan Kiss <zoltan.kiss@xxxxxxxxxx> wrote:Do you have any feedback on this? I'm also adding KVM list as they might be interested in this. Zoli On 28/02/14 19:16, 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>I do not think this is required, netlink zero copy only maps pre-allocated buffers to user-space. How do you mean "pre-allocated"? By who?As far as I've seen the skb in this function came straight from the device (vif in our case), and skb_zerocopy just copy the frags to user_skb, which is sent to the userspace. Those frags contain pages from guest, and it's a bad idea to pass them to userspace: e.g if userspace dies in the meantime, what happens with them? Also, in Xen's case they are actually not mapped to userspace, so accessing them can lead to garbage. Zoli _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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