linux-kernel - Re: [PATCH 4/6] x86/mtrr: don't let mtrr_type_lookup() return MTRR_TYPE

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Date:   Tue, 7 Feb 2023 08:20:31 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        lists@...dbynature.de, mikelley@...rosoft.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 4/6] x86/mtrr: don't let mtrr_type_lookup() return MTRR_TYPE_INVALID

On Mon, Feb 6, 2023 at 11:29 PM Juergen Gross <jgross@...e.com> wrote:
>
> mtrr_type_lookup() should always return a valid memory type. In case
> there is no information available, it should return the default UC.

Why isn't the second case (ie MTRR_STATE_MTRR_ENABLED not being set)
returning 'mtrr_state.def_type'. That's what the hw does, no?

> At the same time the mtrr_type_lookup() stub for the !CONFIG_MTRR
> case should set uniform to 1, as if the memory range would be
> covered by no MTRR at all.

.. but you didn't do that for the CONFIG_MTRR, so now they return
MTRR_TYPE_UNCACHABLE, but don't set uniform=1.

              Linus