Re: data corruption with nvidia chipsets and IDE/SATA drives (k8 cpu errata needed?)

[Chip Coldwell <coldwell@redhat.com>]

On Wed, 17 Jan 2007, Andi Kleen wrote:

> On Wednesday 17 January 2007 07:31, Chris Wedgwood wrote:
> > On Tue, Jan 16, 2007 at 08:52:32PM +0100, Christoph Anton Mitterer wrote:
> > > I agree,... it seems drastic, but this is the only really secure
> > > solution.
> >
> > I'd like to here from Andi how he feels about this?  It seems like a
> > somewhat drastic solution in some ways given a lot of hardware doesn't
> > seem to be affected (or maybe in those cases it's just really hard to
> > hit, I don't know).
>
> AMD is looking at the issue. Only Nvidia chipsets seem to be affected,
> although there were similar problems on VIA in the past too.
> Unless a good workaround comes around soon I'll probably default
> to iommu=soft on Nvidia.
>
> -Andi
> -
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We've just verified that configuring the graphics aperture to be
write-combining instead of write-back using an MTRR also solves the
problem.  It appears to be a cache incoherency issue in the graphics
aperture.

This script does the trick:

[ -- cut here -- ]
#!/bin/bash

# Read the northbridge offset 0x90 to get the size of the aperture
size=0x`lspci -xxx -s 0:18.3 | awk '/^90:/ { print $2 }'`

# bit 0 indicates the aperture is enabled, bits 1 - 3 indicate the size
if [ $((size & 1)) -eq 0 ] ; then
    echo "GART disabled; exiting"
    exit 0
fi

shft=$(((size >> 1) & 7))
size=$((0x2000000 << shft))

# Read the northbridge offset 0x94 to get the base address of the aperture
base=0x`lspci -xxx -s 0:18.3 | awk '/^90:/ { print $6 }'`
base=$((base << 25))
basehex=`printf 0x%08x $base`

printf "IOMMU aperture found at base=0x%08x size=0x%08x (%d KiB)\n" $base $size $((size/1024))

if grep -q $basehex /proc/mtrr ; then
    echo "MTRR already configured for IOMMU aperture; exiting"
    exit 0
fi

echo "Configuring write-combining MTRR for IOMMU aperture"
printf "base=0x%08x size=0x%08x type=write-combining\n" $base $size >/proc/mtrr

exit 0
[ -- cut here-- ]

Chip

--
Charles M. "Chip" Coldwell
Senior Software Engineer
Red Hat, Inc
978-392-2426

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