linux-kernel - Re: [PATCH v2 02/10] x86/mtrr: remove unused cyrix_set

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Message-ID: <6b830ad8-1406-b740-27ba-f1161df99b0f@suse.com>
Date:   Thu, 25 Aug 2022 14:13:03 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        linux-kernel@...r.kernel.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 v2 02/10] x86/mtrr: remove unused cyrix_set_all() function

On 25.08.22 13:42, Borislav Petkov wrote:
> On Thu, Aug 25, 2022 at 12:41:05PM +0200, Juergen Gross wrote:
>> Maybe the alternative reasoning is much faster to understand: if the
>> Cyrix set_all() could be called, the AMD and Centaur ones would be callable,
>> too.
> 
> Right.
> 
>> Those being called would result in a NULL deref, so why should we keep
>> the Cyrix one?
> 
> I know you're eager to remove dead code - I'd love that too. But before
> we do that, we need to find out whether some Cyrix hw out there would
> not need this.

Back to reasoning #1. Only the use_intel() case calls the code in question
with reg == ~0. And use_intel() is clearly not Cyrix.


Juergen

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