Re: [Xen-devel] Re: [PATCH 06/16] xen: disable PAT

[Ingo Molnar <mingo@xxxxxxx>]

* H. Peter Anvin <hpa@xxxxxxxxx> wrote:

> Alan Cox wrote:
> > 
> > There are quite a few different CPUs with PAT errata. I've no idea why
> > there are so many errata about that specific bit.
> > 
> 
> I suspect it is simply because:
> 
> a) it moves around between the various page table formats;
> b) the default configuration and existing OSes don't use it;
> c) it isn't even *present* in some formats.

I also suspect those bits is also on the TLB miss critical path so 
there's probably quite a bit of extra complexity around it on the 
hardware side to keep the latency down.

        Ingo

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