On 14 Dec, 00:50, Andi Kleen <[email protected]> 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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