From: Wei Liu <wei.liu2@citrix.com>
To: annie li <annie.li@oracle.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
Ian Campbell <Ian.Campbell@citrix.com>,
"konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
David Vrabel <david.vrabel@citrix.com>,
"jbeulich@suse.com" <jbeulich@suse.com>,
"wdauchy@gmail.com" <wdauchy@gmail.com>
Subject: Re: [Xen-devel] [PATCH V5 6/7] xen-netback: coalesce slots in TX path and fix regressions
Date: Wed, 1 May 2013 10:22:11 +0100 [thread overview]
Message-ID: <20130501092211.GA9780@zion.uk.xensource.com> (raw)
In-Reply-To: <51800809.9070407@oracle.com>
On Tue, Apr 30, 2013 at 07:06:01PM +0100, annie li wrote:
>
> On 2013-4-15 13:06, Wei Liu wrote:
> > This patch tries to coalesce tx requests when constructing grant copy
> > structures. It enables netback to deal with situation when frontend's
> > MAX_SKB_FRAGS is larger than backend's MAX_SKB_FRAGS.
> >
> > With the help of coalescing, this patch tries to address two regressions and
> > avoid reopening the security hole in XSA-39.
> >
> > Regression 1. The reduction of the number of supported ring entries (slots)
> > per packet (from 18 to 17). This regression has been around for some time but
> > remains unnoticed until XSA-39 security fix. This is fixed by coalescing
> > slots.
> >
> > Regression 2. The XSA-39 security fix turning "too many frags" errors from
> > just dropping the packet to a fatal error and disabling the VIF. This is fixed
> > by coalescing slots (handling 18 slots when backend's MAX_SKB_FRAGS is 17)
> > which rules out false positive (using 18 slots is legit) and dropping packets
> > using 19 to `max_skb_slots` slots.
> >
> > To avoid reopening security hole in XSA-39, frontend sending packet using more
> > than max_skb_slots is considered malicious.
> >
> > The behavior of netback for packet is thus:
> >
> > 1-18 slots: valid
> > 19-max_skb_slots slots: drop and respond with an error
> > max_skb_slots+ slots: fatal error
> >
> > max_skb_slots is configurable by admin, default value is 20.
> >
> > Also change variable name from "frags" to "slots" in netbk_count_requests.
> >
> > Please note that RX path still has dependency on MAX_SKB_FRAGS. This will be
> > fixed with separate patch.
>
> Wei,
>
> The RX path dependency on MAX_SKB_FRAGS in netback should not cause
> packet dropping issue like TX path, RX path only calls netif_stop_queue
> if RX ring is full.
> What is your plan on RX path? Is it in your schedule or you started it
> already?
>
Not yet planned or started. My general idea is that we need to remove
all dependency on MAX_SKB_FRAGS.
I'm working on bug fix for libxl now, so I might get to that later.
Wei.
> Thanks
> Annie
next prev parent reply other threads:[~2013-05-01 9:22 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-15 17:06 [PATCH V5 0/7] Bundle fixes for Xen netfront /netback Wei Liu
2013-04-15 17:06 ` [PATCH V5 1/7] xen-netfront: remove unused variable `extra' Wei Liu
2013-04-15 17:06 ` [PATCH V5 2/7] xen-netfront: frags -> slots in xennet_get_responses Wei Liu
2013-04-15 17:06 ` [PATCH V5 3/7] xen-netback: remove skb in xen_netbk_alloc_page Wei Liu
2013-04-15 17:06 ` [PATCH V5 4/7] xen-netfront: frags -> slots in log message Wei Liu
2013-04-17 13:48 ` Ian Campbell
2013-04-15 17:06 ` [PATCH V5 5/7] xen-netfront: reduce gso_max_size to account for max TCP header Wei Liu
2013-04-17 13:51 ` Ian Campbell
2013-04-15 17:06 ` [PATCH V5 6/7] xen-netback: coalesce slots in TX path and fix regressions Wei Liu
2013-04-17 13:53 ` Ian Campbell
2013-04-21 22:06 ` annie li
2013-04-22 9:28 ` Wei Liu
2013-04-30 18:06 ` [Xen-devel] " annie li
2013-05-01 9:22 ` Wei Liu [this message]
2013-04-15 17:06 ` [PATCH V5 7/7] xen-netback: don't disconnect frontend when seeing oversize packet Wei Liu
2013-04-15 17:38 ` [PATCH V5 0/7] Bundle fixes for Xen netfront /netback David Miller
2013-04-17 13:49 ` Ian Campbell
2013-04-17 17:05 ` David Miller
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