Re: 2.6.26-rc1 lies about PAT not being available

[H. Peter Anvin]

Ingo Molnar wrote:
> > I know about Intel's PAT erratum (only 4 PAT entries work) and 
> > understand that the kernel might not want to use a half-broken PAT 
> > implementation, but the statement above is blatantly false: the kernel 
> > IS built with PAT support and the CPU DOES have (half-broken) PAT HW 
> > support as /proc/cpuinfo from earlier kernels confirms.
>
> well the code is just being overly conservative, and the message is 
> right: the kernel does not support PAT on that hw. Yet.
>
> Please send us a patch and test whether it's working on your box? That's 
> how the PAT code evolved: it initially was only enabled on a very small 
> subset of CPUs. We can enable it on more CPUs if people test it.
>
> To be conservative, please make the code emit a printk that this is PAT 
> on not fully-working hw platform (only 4 PAT entries work). If there 
> _is_ some erratum on that CPU affecting PAT reliability down the line, 
> we at least want to have some clue in the syslog.

For what it's worth, we only use four PAT entries, so it doesn't matter 
that only four work.

	-hpa

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