breakage with c/s 19950

[Christoph Egger <Christoph.Egger@amd.com>]

Hi Jan!

In c/s 19950, you disable the GART TLB walk error of the northbridge
as a workaround for AMD K8 CPUs. The comment says, it happens with IOMMU & 
3ware & Cerberus.

There's a Linux/Dom0 boot problem with this:

The Linux/Dom0 kernel also has this workaround which leads to a #GP in the 
guest because in Xen mce.c:mce_wrmsr() returns -1.

The question is, is the workaround really really necessary ?
IOMMU is not yet on market and if there will be AMD K8 machines with
an IOMMU is very questionable.

If the workaround is not needed, please remove it from both Linux and Xen.
If the workaround is valid, then mce.c:mce_wrmsr() needs a special check
for this workaround to NOT return -1.

Christoph


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