Re: [PATCH] X86: MM: Add PAT Type write-through in combination with mtrr

Andreas Werner
2013-10-28T12:04:07Z

On Mon, Oct 28, 2013 at 12:45:41PM +0100, Borislav Petkov wrote:
> Drop Dave's stale mail address.
>
> On Mon, Oct 28, 2013 at 12:25:05PM +0100, Andreas Werner wrote:
> > > but you end up doing
> > >
> > > PAT=Write-Back + MTRR=Write-Through = Effective Memory of Write-Back
> > >
> > No the effective memory type is WT, check out the Intel document with the
> > table of Effective memory type combinations.
>
> You need to read what I'm saying more carefully.
Sorry then i missunderstood something?
>
> > Yes but, there is no way in the kernel to mark a memory WT,
>
> That doesn't mean you can return _PAGE_CACHE_WB for MTRR_TYPE_WRTHROUGH.
> The correct thing to do, IMHO, would be to set the PWT bit in the PTEs
> of those pages comprising your buffer.
>
But why? the combination of PAT=WB and MTRR=WT is allowed isn´t it?
What should i return instead of?

regards
Andy
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