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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Mon, 13 Jan 2020 22:50:59 +0100
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Subject: Re: [RFC PATCH V2 11/11] x86: tsc: avoid system instability in hibernation
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "Singh, Balbir" <sblbir@amazon.com>,
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On Mon, Jan 13, 2020 at 1:43 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Jan 13, 2020 at 11:43:18AM +0000, Singh, Balbir wrote:
> > For your original comment, just wanted to clarify the following:
> >
> > 1. After hibernation, the machine can be resumed on a different but compatible
> > host (these are VM images hibernated)
> > 2. This means the clock between host1 and host2 can/will be different
> >
> > In your comments are you making the assumption that the host(s) is/are the
> > same? Just checking the assumptions being made and being on the same page with
> > them.
>
> I would expect this to be the same problem we have as regular suspend,
> after power off the TSC will have been reset, so resume will have to
> somehow bridge that gap. I've no idea if/how it does that.

In general, this is done by timekeeping_resume() and the only special
thing done for the TSC appears to be the tsc_verify_tsc_adjust(true)
call in tsc_resume().

> I remember some BIOSes had crazy TSC ideas for suspend2ram, and we grew
> tsc_restore_sched_clock_state() for it.
>
> Playing crazy games like what you're doing just isn't it though.

Right.