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

Pavel Machek
2008-12-20T11:32:27Z

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@amd.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@amd.com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@suse.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?)

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