linux-kernel - RE: [PATCH 5/6] x86/mm: only check uniform after calling mtrr_type

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Message-ID: <PH7PR84MB18382D0F717742662E520AC782D89@PH7PR84MB1838.NAMPRD84.PROD.OUTLOOK.COM>
Date:   Wed, 8 Feb 2023 01:13:05 +0000
From:   "Kani, Toshi" <toshi.kani@....com>
To:     Borislav Petkov <bp@...en8.de>, Juergen Gross <jgross@...e.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "lists@...dbynature.de" <lists@...dbynature.de>,
        "mikelley@...rosoft.com" <mikelley@...rosoft.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: RE: [PATCH 5/6] x86/mm: only check uniform after calling
 mtrr_type_lookup()

On 07.02.23 12:42, Borislav Petkov wrote:
> On Tue, Feb 07, 2023 at 08:29:01AM +0100, Juergen Gross wrote:
> > Today pud_set_huge() and pmd_set_huge() test for the MTRR type to be
> > WB or INVALID after calling mtrr_type_lookup(). Those tests can be
> > dropped, as the only reason to not use a large mapping would be
> > uniform being 0. Any MTRR type can be accepted as long as it applies
> > to the whole memory range covered by the mapping, as the alternative
> > would only be to map the same region with smaller pages instead using
> > the same PAT type as for the large mapping.
:
> Lemme add Toshi who authored that code - he might have a comment or
> two.

The current mtrr_type_look() does not set 'uniform' for MTRR_TYPE_INVALID.
Please also update it to set 'uniform', if not done in other patches.

Toshi