Re: PAT support

[Andi Kleen <ak@muc.de>]

> This would also be extremely useful on machines with large amounts
> of memory, for write-back mappings.  With large amounts but odd sized
> entries it becomes extremely tricky to map all of the memory using
> mtrrs.

Yes agreed. I already had vendors complaining about this.
But for this it will need some more work - the MTRRs need to be fully
converted to PAT and then disabled (because MTRRs have 
higher priority than PAT). Doing so is a lot more risky than 
what Terrence's patch does currently though.  But longer term
we will need it.

Also it will still need to handle overlapping ranges. I suppose
it will need some simple rules like: converting from UC to WC is 
always ok.

-Andi