linux-kernel - Re: [patch 01/22] AMD IOMMU: enable device isolation per default

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Message-ID: <20081220112613.GA7480@ucw.cz>
Date:	Sat, 20 Dec 2008 12:26:14 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	stable@...nel.org, Justin Forbes <jmforbes@...uxtx.org>,
	Zwane Mwaikambo <zwane@....linux.org.uk>,
	Theodore Ts'o <tytso@....edu>,
	Randy Dunlap <rdunlap@...otime.net>,
	Dave Jones <davej@...hat.com>,
	Chuck Wolber <chuckw@...ntumlinux.com>,
	Chris Wedgwood <reviews@...cw.f00f.org>,
	Michael Krufky <mkrufky@...uxtv.org>,
	Chuck Ebbert <cebbert@...hat.com>,
	Domenico Andreoli <cavokz@...il.com>, Willy Tarreau <w@....eu>,
	Rodrigo Rubira Branco <rbranco@...checkpoint.com>,
	Jake Edge <jake@....net>, Eugene Teo <eteo@...hat.com>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk
Subject: Re: [patch 01/22] AMD IOMMU: enable device isolation per default

On Fri 2008-12-19 12:21:37, Joerg Roedel wrote:
> On Thu, Dec 18, 2008 at 02:00:15PM +0100, Pavel Machek wrote:
> > On Tue 2008-12-16 16:03:53, Greg KH wrote:
> > > 2.6.27-stable review patch.  If anyone has any objections, please let us know.
> > > 
> > > ------------------
> > > 
> > > From: Joerg Roedel <joerg.roedel@....com>
> > > 
> > > commit 3ce1f93c6d53c3f91c3846cf66b018276c8ac2e7 upstream.
> > > 
> > > Impact: makes device isolation the default for AMD IOMMU
> > > 
> > > Some device drivers showed double-free bugs of DMA memory while testing
> > > them with AMD IOMMU. If all devices share the same protection domain
> > > this can lead to data corruption and data loss. Prevent this by putting
> > > each device into its own protection domain per default.
> > > 
> > > Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
> > 
> > This does not look like 'fix for a serious bug' to
> > me. stable_kernel_rules.txt says '...not a "this could be a problem"
> > type thing'.
> 
> So you don't consider lost data because your filesystem is corrupted
> as a problem? This is exactly what can happen (and I suffered from it
> one time) if you use IOMMU with a buggy driver (typically a network card
> driver).

If you have buggy driver, _you have to fix the driver_, not work
around it by iommu magic that only few machines can do.

So this fixes nothing. (But it helps mask bugs in other pieces of
code/hw. Good. But for stable?)

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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