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

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Message-ID: <20131028120358.GE2278@thinkpad.fritz.box>
Date:	Mon, 28 Oct 2013 13:03:58 +0100
From:	Andreas Werner <wernerandy@....de>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Ingo Molnar <mingo@...nel.org>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] X86: MM: Add PAT Type write-through in combination with
 mtrr

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
> -- 
> Regards/Gruss,
>     Boris.
> 
> Sent from a fat crate under my desk. Formatting is fine.
> --
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