From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tim Deegan Subject: Re: Xen Advisory 5 (CVE-2011-3131) IOMMU fault livelock Date: Mon, 15 Aug 2011 10:26:08 +0100 Message-ID: <20110815092608.GD11708@ocelot.phlegethon.org> References: <20037.10841.995717.397090@mariner.uk.xensource.com> <4E454C880200007800051000@nat28.tlf.novell.com> <20110812140901.GC11708@ocelot.phlegethon.org> <4E4559440200007800051062@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Return-path: Content-Disposition: inline In-Reply-To: <4E4559440200007800051062@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: xen-devel@lists.xensource.com, "Xen.org security team" List-Id: xen-devel@lists.xenproject.org At 15:48 +0100 on 12 Aug (1313164084), Jan Beulich wrote: > >>> On 12.08.11 at 16:09, Tim Deegan wrote: > > At 14:53 +0100 on 12 Aug (1313160824), Jan Beulich wrote: > >> > This issue is resolved in changeset 23762:537ed3b74b3f of > >> > xen-unstable.hg, and 23112:84e3706df07a of xen-4.1-testing.hg. > >> > >> Do you really think this helps much? Direct control of the device means > >> it could also (perhaps on a second vCPU) constantly re-enable the bus > >> mastering bit. > > > > That path goes through qemu/pciback, so at least lets Xen schedule the > > dom0 tools. > > Are you sure? If (as said) the guest uses a second vCPU for doing the > config space accesses, I can't see how this would save the pCPU the > fault storm is occurring on. Hmmm. Yes, I see what you mean. What was your concern about memory-mapped config registers? That PCIback would need to be involved somehow? > > The particular failure that this patch fixes was locking up > > cpu0 so hard that it couldn't even service softirqs, and the NMI > > watchdog rebooted the machine. > > Hmm, that would point at a flaw in the interrupt exit path, on which > softirqs shouldn't be ignored. Are you suggesting that we should handle softirqs before re-enabling interrupts? That sounds perilous. Tim. -- Tim Deegan Principal Software Engineer, Xen Platform Team Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)