linux-kernel - Re: [PATCH v4 07/16] x86/mtrr: split generic_set

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Date:   Wed, 26 Oct 2022 12:37:53 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v4 07/16] x86/mtrr: split generic_set_all()

On Tue, Oct 04, 2022 at 10:10:14AM +0200, Juergen Gross wrote:
> Split generic_set_all() into multiple parts, while moving the main
> function body into cacheinfo.c.
> 
> Prepare the support of PAT without needing MTRR support by
> moving the main function body of generic_set_all() into cacheinfo.c
> while renaming it to cache_cpu_init(). The MTRR specific parts are
> moved into a dedicated small function called by cache_cpu_init() in
> order to make cache_cpu_init() as MTRR agnostic as possible.
> 
> The setting of smp_changes_mask is merged into the (new) function
> mtrr_generic_set_state() used to call set_mtrr_state(). It was
> probably split in ancient times, as atomic operations while running
> uncached might be quite expensive, but OTOH only systems with a
> broken BIOS should ever require to set any bit in smp_changes_mask,
> so just hurting those devices with a penalty of a few microseconds
> during boot shouldn't be a real issue.

This still needs addressing

"So the commit message should not say what you're doing - that should
be visible from the diff itself. It should talk more about the *why*
you're doing it."

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette