linux-kernel - Re: [RFC 1/2] x86/tsc: add a timer to make sure tsc

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Message-ID: <20210410094752.GB21691@zn.tnic>
Date:   Sat, 10 Apr 2021 11:47:52 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Feng Tang <feng.tang@...el.com>, Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, rui.zhang@...el.com,
        andi.kleen@...el.com, dave.hansen@...el.com, len.brown@...el.com
Subject: Re: [RFC 1/2] x86/tsc: add a timer to make sure tsc_adjust is always
 checked

On Sat, Apr 10, 2021 at 11:27:11AM +0200, Thomas Gleixner wrote:
> On Tue, Mar 30 2021 at 16:25, Feng Tang wrote:
> > Normally the tsc_sync will be checked every time system enters idle state,
> > but there is still caveat that a system won't enter idle, either because
> > it's too busy or configured purposely to not enter idle. Setup a periodic
> > timer to make sure the check is always on.
> 
> Bah. I really hate the fact that we don't have a knob to disable writes
> to the TSC/TSC_ADJUST msrs. That would spare this business alltogether.

We have the MSR filtering and I'd *love* to add those MSRs to a
permanent ban list of MSRs which will never ever be written to from
luserspace.

-- 
Regards/Gruss,
    Boris.

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