linux-kernel - Re: Interaction between Xen and XFS: stray RW mappings

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: <1193004961.6745.42.camel@pasglop>
Date:	Mon, 22 Oct 2007 08:16:01 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>, David Chinner <dgc@....com>,
	Jeremy Fitzhardinge <jeremy@...p.org>, xfs@....sgi.com,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mark Williamson <mark.williamson@...cam.ac.uk>,
	Morten BÃ¸geskov 
	<xen-users@...ten.bogeskov.dk>, xfs-masters@....sgi.com
Subject: Re: Interaction between Xen and XFS: stray RW mappings


On Mon, 2007-10-15 at 13:07 +0200, Andi Kleen wrote:
> On Tue, Oct 16, 2007 at 12:56:46AM +1000, Nick Piggin wrote:
> > Is this true even if you don't write through those old mappings?
> 
> I think it happened for reads too.  It is a little counter intuitive
> because in theory the CPU doesn't need to write back non dirty lines,
> but in the one case which took so long to debug exactly this happened
> somehow.

The problem exist also on ppc, and afaik, is due to the line being in
the cache at all (either dirty (write) or not (read)), thus causing the
snoop logic to hit, that is what's causing the problem vs. non cached
accesses.

Also, on some processors, the simple fact of having the page mapped can
cause the CPU to prefetch from it even if it's not actually accessed
(speculative prefetch can cross page boundaries if things are mapped).

Ben.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/