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

From: Borislav Petkov
Date: Tue May 12 2015 - 12:31:57 EST

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))

if ((mtrr != MTRR_TYPE_INVALID) && (!uniform) && (mtrr != MTRR_TYPE_WRBACK))

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.


ECO tip #101: Trim your mails when you reply.
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