netdev - Re: [PATCH] net: xen-netback: convert to hw

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1303226148.5997.233.camel@zakaz.uk.xensource.com>
Date:	Tue, 19 Apr 2011 16:15:48 +0100
From:	Ian Campbell <Ian.Campbell@...citrix.com>
To:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH] net: xen-netback: convert to hw_features

On Tue, 2011-04-19 at 14:43 +0100, Michał Mirosław wrote:
> On Tue, Apr 19, 2011 at 02:39:00PM +0100, Ian Campbell wrote:
> > On Tue, 2011-04-19 at 14:30 +0100, Michał Mirosław wrote:
> > > On Tue, Apr 19, 2011 at 02:17:53PM +0100, Ian Campbell wrote:
> > > > I fixed it with the following, I also moved the !can_sg MTU clamping
> > > > into a set_features hook (like we do with netfront). Am I right that
> > > > this pattern copes with changes to SG via ethtool etc better? I think
> > > > it's more future proof in any case.
> > > This looks wrong. Even if SG is turned on, you might get big skbs which
> > > are linearized. There is a difference in SG capability and SG offload
> > > status and as I see it the capability is what you need to test for MTU.
> > So the existing stuff in drivers/net/xen-netfront.c is wrong too?
> 
> Looks like it. But I don't really know what are the real constraints for MTU.
> What I know is that SG even if turned on needs not be used (and currently
> it's not e.g. if checksum offload is disabled).

The interesting case is the opposite one, isn't it? IOW if NETIF_F_SG is
disabled but the frontend/backend agree that they have the capability to
handle >PAGE_SIZE skbs

In my experience, the normal reason for disabling the NETIF_F_SG offload
status is that the underlying capability is somehow buggy, otherwise is
there any reason to turn it off?

> So MTU setting should not depend on SG offload state but on some capability.

Ian.


--
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