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Message-ID: <20210410144856.GC22054@shbuild999.sh.intel.com>
Date: Sat, 10 Apr 2021 22:48:56 +0800
From: Feng Tang <feng.tang@...el.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>,
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
Hi Boris,
On Sat, Apr 10, 2021 at 11:47:52AM +0200, Borislav Petkov wrote:
> 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.
Yep, I just tried changing TSC_ADJUST msr with 'wrmsr' command, and
it did succeed and trigger the warning of tsc_verify_tsc_adjust():
[ 1135.387866] [Firmware Bug]: TSC ADJUST differs: CPU0 0 --> 4096. Restoring
And the bigger risk is still BIOS's writing to TSC_ADJUST MSR beneath
kernel.
Thanks,
Feng
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette
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