linux-kernel - Re: [PATCH 2/2] x86/pat: add functions to query specific cache mode availability

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Message-ID: <YoT4Zk/SxBgadq2b@infradead.org>
Date:   Wed, 18 May 2022 06:45:10 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, jbeulich@...e.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>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 2/2] x86/pat: add functions to query specific cache mode
 availability

On Tue, May 03, 2022 at 03:22:07PM +0200, Juergen Gross wrote:
> Some drivers are using pat_enabled() in order to test availability of
> special caching modes (WC and UC-). This will lead to false negatives
> in case the system was booted e.g. with the "nopat" variant and the
> BIOS did setup the PAT MSR supporting the queried mode, or if the
> system is running as a Xen PV guest.
> 
> Add test functions for those caching modes instead and use them at the
> appropriate places.
> 
> For symmetry reasons export the already existing x86_has_pat_wp() for
> modules, too.

No, we never export unused functionality.