linux-kernel - Re: [PATCH v4 2/7] mtrr, x86: Fix MTRR lookup to handle inclusive entry

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Date:	Tue, 05 May 2015 13:31:32 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	akpm@...ux-foundation.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com, linux-mm@...ck.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, dave.hansen@...el.com,
	Elliott@...com, pebolle@...cali.nl
Subject: Re: [PATCH v4 2/7] mtrr, x86: Fix MTRR lookup to handle inclusive
 entry

On Tue, 2015-05-05 at 20:39 +0200, Borislav Petkov wrote:
> On Tue, May 05, 2015 at 11:32:08AM -0600, Toshi Kani wrote:
> > > Ok, I'm confused. Shouldn't the inclusive:1 case be
> > > 
> > > 			(start:mtrr_start) (mtrr_start:mtrr_end) (mtrr_end:end)
> > > 
> > > ?
> > > 
> > > If so, this function would need more changes...
> > 
> > Yes, that's how it gets separated eventually.  Since *repeat is set in
> > this case, the code only needs to separate the first part at a time.
> > The 2nd part gets separated in the next call with the *repeat.
> 
> Aah, right, the caller is supposed to adjust the interval limits on
> subsequent calls. Please reflect this in the comment because:
> 
> 		*     (start:mtrr_start) (mtrr_start:end)
> 
> is misleading for inclusive:1.

Well, the comment kinda says it already, but I will try to clarify it.

           /*
            * We have start:end spanning across an MTRR.
            * We split the region into either
            * - start_state:1
            *     (start:mtrr_end) (mtrr_end:end)
            * - end_state:1 or inclusive:1
            *     (start:mtrr_start) (mtrr_start:end)
            * depending on kind of overlap.
            * Return the type for first region and a pointer to
            * the start of second region so that caller will
            * lookup again on the second region.
            * Note: This way we handle multiple overlaps as well.
            */

Thanks,
-Toshi

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