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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Peter Zijlstra <peterz@infradead.org>, bigeasy@linutronix.de
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Subject: Re: [PATCH v2 08/13] x86/vdso: Fix gettimeofday masking
In-Reply-To: <87r0qwfrm0.ffs@tglx>
References: <20230519102058.581557770@infradead.org>
 <20230519102715.704767397@infradead.org> <87r0qwfrm0.ffs@tglx>
Date:   Thu, 01 Jun 2023 00:46:20 +0200
Message-ID: <87y1l4dsqr.ffs@tglx>
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On Wed, May 31 2023 at 17:27, Thomas Gleixner wrote:
> On Fri, May 19 2023 at 12:21, Peter Zijlstra wrote:
>> to take wrapping into account, but per all the above, we don't
>> actually wrap on u64 anymore.
>
> Indeed. The rationale was that you need ~146 years uptime with a 4GHz
> TSC or ~584 years with 1GHz to actually reach the wrap around point.
>
> Though I can see your point to make sure that silly BIOSes or VMMs
> cannot cause havoc by accident or malice.
>
> Did anyone ever validate that wrap around on TSC including TSC deadline
> timer works correctly?
>
> I have faint memories of TSC_ADJUST, which I prefer not to bring back to
> main memory :)

It seems my fears have been unjustified.

At least a quick test which sets the TSC to ~ -8min @2.1Ghz the machine
seems to survive without the colourful explosions I expected due to my
early exposure to TSC_ADJUST and TSC_DEADLINE_TIMER :)

Thanks,

        tglx