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DateMon, 17 Dec 2007 10:40:33 +0000
From"Daniel J Blueman" <>
SubjectRe: PAT 64b: Basic PAT implementation
On 14 Dec, 00:50, Andi Kleen <a...@muc.de> wrote:
> > +void __cpuinit pat_init(void)> > +{> > +  /* Set PWT+PCD to Write-Combining. All other bits stay the same */
> > +  if (cpu_has_pat) {>> All the old CPUs (PPro etc.) with known PAT bugs need to clear this flag
> now in their CPU init functions. It is fine to be aggressive there
> because these old systems have lived so long without PAT they can do
> so forever. So perhaps it's best to just white list it only for newer
> CPUs on the Intel side at least.

> Another problem is that there are some popular modules (ATI, Nvidia for once)
> who reprogram the PAT registers on their own, likely different. Need some way to detect
> that case I guess, otherwise lots of users will see strange malfunctions.
> Maybe recheck after module load?

This may not be as big problem as thought, since sane and at least one
vendor driver (Quadrics QsNetII) searches the PAT slots for a WC entry
- where this has already been setup by the kernel, it'll use the right
one.

> > +                   |||> > +             000 WB         default> > +             010 UC_MINUS   _PAGE_PCD> > +             011 WC         _PAGE_WC> > +             PAT bit unused */> > +          pat = PAT(0,WB) | PAT(1,WT) | PAT(2,UC_MINUS) | PAT(3,WC) |
> > +                PAT(4,WB) | PAT(5,WT) | PAT(6,UC_MINUS) | PAT(7,WC);
> > +          rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
> > +          wrmsrl(MSR_IA32_CR_PAT, pat);> > +          __flush_tlb_all();> > +          asm volatile("wbinvd");>> Have you double checked this is the full procedure from the manual? iirc there
> were some steps missing.>> -Andi
-- 
Daniel J Blueman


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