Re: [PATCH] i386, x86_64 Initial PAT implementation

Andi Kleen
2005-08-30T14:50:30Z

On Tuesday 30 August 2005 16:45, Alan Cox wrote:
> On Llu, 2005-08-29 at 18:20 -0600, Eric W. Biederman wrote:
> > ways. Currently this code only allows for an additional flavor
> > of uncached access to physical memory addresses which should be hard
> > to abuse, and should raise no additional aliasing problems. No
> > attempt has been made to fix theoretical aliasing problems.
>
> Even an uncached/cached alias causes random memory corruption or an MCE
> on x86 systems. In fact it can occur even for an alias not in theory
> touched by the CPU if it happens to prefetch into or speculate the
> address.
>
> Also be sure to read the PII Xeon errata - early PAT has a bug or two.

We can always force cpu_has_pat == 0 on these machines.
I don't think it is worth it to add any more complicated workarounds
for old broken systems.

-Andi