linux-kernel - Re: [PATCH 0/2] fix kernel crash with macvtap on top of LRO

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Message-ID: <1360276295.3605.44.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Thu, 7 Feb 2013 22:31:35 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	David Miller <davem@...emloft.net>, <eric.dumazet@...il.com>,
	<netdev@...r.kernel.org>, <eilong@...adcom.com>,
	<jeffrey.t.kirsher@...el.com>, <jesse.brandeburg@...el.com>,
	<bruce.w.allan@...el.com>, <carolyn.wyborny@...el.com>,
	<donald.c.skidmore@...el.com>, <gregory.v.rose@...el.com>,
	<peter.p.waskiewicz.jr@...el.com>, <alexander.h.duyck@...el.com>,
	<john.ronciak@...el.com>, <tushar.n.dave@...el.com>,
	<jitendra.kalsaria@...gic.com>, <sony.chacko@...gic.com>,
	<linux-driver@...gic.com>, <john.r.fastabend@...el.com>,
	<jacob.e.keller@...el.com>, <linux-kernel@...r.kernel.org>,
	<e1000-devel@...ts.sourceforge.net>
Subject: Re: [PATCH 0/2] fix kernel crash with macvtap on top of LRO

On Thu, 2013-02-07 at 23:33 +0200, Michael S. Tsirkin wrote:
> On Thu, Feb 07, 2013 at 01:14:20PM -0500, David Miller wrote:
> > From: Ben Hutchings <bhutchings@...arflare.com>
> > Date: Thu, 7 Feb 2013 16:20:46 +0000
> > 
> > > If the consensus is still that we must preserve packets exactly (aside
> > > from the usual modifications by IP routers) then LRO should be disabled
> > > on all devices for which forwarding is enabled.
> > 
> > I believe this is still undoubtedly the consensus.
> 
> But we don't need to preserve the packets when passing them to macvtap
> (which discards all this info smashing the packet into a single buffer anyway),
> correct?

macvtap_skb_to_vnet_hdr() certainly seems to be trying to preserve all
the packet information.

> If true LRO with macvtap might be useful and so the patchset is probably
> still the right thing to do to fix the macvtap crash. Makes sense?

If macvtap+virtio_net is expected to re-segment then this is fine.  But
I don't see why it should be different from other uses of macvlan.

> We might want to add code to forward LRO status from macvlan
> (not macvtap) back to the lowerdev, so that setting up forwarding
> from macvlan disables LRO on the lowerdev, but that seems like another
> issue.

I think it's the same issue!

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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