Re: [patch 4/8] x86/tsc: Verify TSC_ADJUST from idle

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [patch 4/8] x86/tsc: Verify TSC_ADJUST from idle
Date	2016-11-21 12:10 +0100
Message-ID	<sFUE1-pB-9@gated-at.bofh.it> (permalink)
References	<sFelr-5AY-3@gated-at.bofh.it> <sFelr-5AY-7@gated-at.bofh.it> <sFAci-2Z1-9@gated-at.bofh.it> <sFRZw-7a5-19@gated-at.bofh.it>
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On Mon, Nov 21, 2016 at 09:16:44AM +0100, Thomas Gleixner wrote:
> On Sun, 20 Nov 2016, Peter Zijlstra wrote:
> > On Sat, Nov 19, 2016 at 01:47:37PM -0000, Thomas Gleixner wrote:
> > > When entering idle, it's a good oportunity to verify that the TSC_ADJUST
> > > MSR has not been tampered with (BIOS hiding SMM cycles). If tampering is
> > > detected, emit a warning and restore it to the previous value.
> > 
> > > +++ b/arch/x86/kernel/process.c
> > > @@ -277,6 +277,7 @@ void exit_idle(void)
> > >  
> > >  void arch_cpu_idle_enter(void)
> > >  {
> > > +	tsc_verify_tsc_adjust();
> > >  	local_touch_nmi();
> > >  	enter_idle();
> > >  }
> > 
> > Doing a RDMSR on the idle path isn't going to be popular. That path is
> > already way too slow.
> 
> Of course we can ratelimit that MSR read with jiffies, but do you have any
> better suggestion aside of doing it timer based?

Not really :/

Thread

[patch 0/8] x86/tsc: Utilize TSC_ADJUST MSR Thomas Gleixner <tglx@linutronix.de> - 2016-11-19 15:00 +0100
  [patch 4/8] x86/tsc: Verify TSC_ADJUST from idle Thomas Gleixner <tglx@linutronix.de> - 2016-11-19 15:00 +0100
    Re: [patch 4/8] x86/tsc: Verify TSC_ADJUST from idle Peter Zijlstra <peterz@infradead.org> - 2016-11-20 14:20 +0100
      Re: [patch 4/8] x86/tsc: Verify TSC_ADJUST from idle Thomas Gleixner <tglx@linutronix.de> - 2016-11-21 09:20 +0100
        Re: [patch 4/8] x86/tsc: Verify TSC_ADJUST from idle Peter Zijlstra <peterz@infradead.org> - 2016-11-21 12:10 +0100
    Re: [patch 4/8] x86/tsc: Verify TSC_ADJUST from idle Andi Kleen <andi@firstfloor.org> - 2016-11-22 00:00 +0100
  [patch 5/8] x86/tsc: Sync test only for the first cpu in a package Thomas Gleixner <tglx@linutronix.de> - 2016-11-19 15:00 +0100
  [patch 3/8] x86/tsc: Store and check TSC ADJUST MSR Thomas Gleixner <tglx@linutronix.de> - 2016-11-19 15:00 +0100
  [patch 1/8] x86/tsc: Use X86_FEATURE_TSC_ADJUST in detect_art() Thomas Gleixner <tglx@linutronix.de> - 2016-11-19 15:00 +0100
  [patch 2/8] x86/tsc: Detect random warps Thomas Gleixner <tglx@linutronix.de> - 2016-11-19 15:00 +0100
  [patch 7/8] x86/tsc: Prepare warp test for TSC adjustment Thomas Gleixner <tglx@linutronix.de> - 2016-11-19 15:00 +0100

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