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Date: Fri, 7 Mar 2014 12:29:34 +0000 From: Zoltan Kiss <zoltan.kiss@...rix.com> To: Pravin Shelar <pshelar@...ira.com> CC: Jesse Gross <jesse@...ira.com>, Thomas Graf <tgraf@...hat.com>, "dev@...nvswitch.org" <dev@...nvswitch.org>, <xen-devel@...ts.xenproject.org>, netdev <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org> Subject: Re: [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@...rix.com> 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@...rix.com> > > 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 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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