Re: PAT support for i386 and x86_64

[Andi Kleen]

> I don't see why we have to worry about cache corruption in the case at
> hand. Write-combining is needed to map io (typically pci-mem regions)
> which are never mapped cachable anywhere, including in the linear map.

If we WC them using PAT then there would be a UC<->WC conflict with
the direct mapping and possibly others. That's already undefined
and not allowed.

After some very bad experiences in the past I'm not going to take
chances on this.

We really need to keep all possible mappings synchronized.

-Andi

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