linux-kernel - Re: [PATCH v2] x86/speculation/srbds: do not try to turn mitigation off when not supported

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Message-ID: <87o81mzhoh.fsf@rcn-XPS-13-9305.i-did-not-set--mail-host-address--so-tickle-me>
Date:   Thu, 31 Mar 2022 09:48:14 +0200
From:   Ricardo Cañuelo <ricardo.canuelo@...labora.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        Mark Gross <mgross@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Johansen <john.johansen@...onical.com>,
        Steve Beattie <sbeattie@...ntu.com>, kernel@...labora.com,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Subject: Re: [PATCH v2] x86/speculation/srbds: do not try to turn mitigation off when not supported

Borislav Petkov <bp@...en8.de> writes:
> So we could also do the below to denote what the situation is and
> therefore clear the bug flag for such CPUs.
>
> The thing is: I want this to be as clear as possible because bugs.c is
> already a nightmare and just slapping more logic to it without properly
> thinking it through is going to be a serious pain to deal with later...

Thanks Boris,

I agree that the more explicit the better, I'll give this a try. I saw
Pawan's suggestion as well but that one is similar to the originally
proposed patch in that the logic/checks are split between two functions,
this solution based on clearing the bug flag seems clearer considering
the comment just before the code block:

	/*
	 * Check to see if this is one of the MDS_NO systems supporting
	 * TSX that are only exposed to SRBDS when TSX is enabled.
	 */

Cheers,
Ricardo