linux-kernel - Re: [PATCH v3] x86/bugs: Explicitly clear speculative MSR bits

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Message-ID: <Y7/iIKl/F8MOrVdD@zn.tnic>
Date:   Thu, 12 Jan 2023 11:34:08 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     Breno Leitao <leitao@...ian.org>, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, hpa@...or.com,
        jpoimboe@...nel.org, peterz@...radead.org, x86@...nel.org,
        cascardo@...onical.com, leit@...a.com, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] x86/bugs: Explicitly clear speculative MSR bits

On Wed, Jan 11, 2023 at 11:00:37PM -0800, Pawan Gupta wrote:
> > SPEC_CTRL_RRSBA_DIS_S is a disable bit and I presume it needs to stay enabled.
> 
> The mitigation is enabled when this bit is set. When set, it prevents RET
> target to be predicted from alternate predictors (BTB). This should stay
> 0, unless enabled by a mitigation mode.
> 
> > Only when spec_ctrl_disable_kernel_rrsba() runs. And I'd say perf-wise it
> > doesn't cost that much...
> 
> I guess this doesn't matter now, because this patch is resetting it by
> default that keeps the mitigation disabled with no perf impact.

Ok, lemme queue it then.

Thx.

-- 
Regards/Gruss,
    Boris.

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