Re: [PATCH v4 7/7] mtrr, mm, x86: Enhance MTRR checks for KVA huge page mapping

From: Toshi Kani
Date: Tue May 12 2015 - 13:16:31 EST

On Tue, 2015-05-12 at 18:31 +0200, Borislav Petkov wrote:
> On Tue, May 12, 2015 at 08:30:30AM -0600, Toshi Kani wrote:
> > MTRR_TYPE_INVALID means MTRRs disabled. So, the caller checking with
> > this value is the same as checking with mtrr_enabled() you suggested.
> So then you don't have to set *uniform = 1 on entry to
> mtrr_type_lookup(). And change the retval test
> if ((!uniform) && (mtrr != MTRR_TYPE_WRBACK))
> to
> if ((mtrr != MTRR_TYPE_INVALID) && (!uniform) && (mtrr != MTRR_TYPE_WRBACK))

Yes, that's what I was thinking as well. Will do.

> You can put the MTRR_TYPE_INVALID first so that it shortcuts.
> You need the distinction between MTRRs *disabled* and an MTRR region
> being {non-,}uniform.
> If MTRRs are disabled, uniform doesn't *mean* *anything* because it is
> undefined. When MTRRs are disabled, the range is *not* covered by MTRRs
> because, well, them MTRRs are disabled.
> And it might be fine for *your* use case to set *uniform even when MTRRs
> are disabled but it might matter in the future. So we better design it
> correct from the beginning.

I think it is a matter of how "uniform" is defined, but your point is
taken and I will change it accordingly.


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