RE: [PATCH v2 2/5] x86/bugs: Use early_param for spectre_v2

[Kaplan, David]

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Borislav Petkov <bp@xxxxxxxxx>
> Sent: Friday, August 22, 2025 9:30 AM
> To: Kaplan, David <David.Kaplan@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>;
> Josh Poimboeuf <jpoimboe@xxxxxxxxxx>; Pawan Gupta
> <pawan.kumar.gupta@xxxxxxxxxxxxxxx>; Ingo Molnar <mingo@xxxxxxxxxx>; Dave
> Hansen <dave.hansen@xxxxxxxxxxxxxxx>; x86@xxxxxxxxxx; H . Peter Anvin
> <hpa@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2 2/5] x86/bugs: Use early_param for spectre_v2
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> On Fri, Aug 22, 2025 at 02:12:55PM +0000, Kaplan, David wrote:
> > It could, but I felt this was a way to logically separate the code vs having
> > one giant function.  All the code in spectre_v2_check_cmd() does one thing:
> > verifies if the chosen command is possible on this system.  The rest of
> > spectre_v2_select_mitigation() then uses the cmd to actually pick
> > a mitigation.
> >
> > Since these were two distinct flows, I thought having a separate function
> > made sense to make the code more readable.  But that was just my opinion,
> > I won't object if you want to inline it.
>
> Right, since we're making all the mitigations handling uniform, I'd prefer to
> have the same code pattern here too. The function does get a bit big but it is
> clear that it does two things: (1) checks the command before it (2) selects
> the mitigation. And the others do the same so...
>

Sort of.  Spectre_v2 is a bit unique is that it is more complicated than almost any other ones in terms of the number of options it has.  There are 11 command line options for spectre_v2, the next closest one has 7.  Spectre_v2 (and spectre_v2_user) are the only remaining mitigations where a 'cmd' is initially chosen instead of a mitigation because of all this complexity and checks that have to occur.

--David Kaplan