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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Tue, 14 Jan 2020 00:30:02 +0100
Message-ID: <CAJZ5v0imNbbch=NWAdgVKf_hjwRrEiWAL8SFNwe6rW_SjgYzrw@mail.gmail.com>
Subject: Re: [RFC PATCH V2 11/11] x86: tsc: avoid system instability in hibernation
To:     Peter Zijlstra <peterz@infradead.org>
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On Mon, Jan 13, 2020 at 10:50 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> 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().

And I forgot about tsc_restore_sched_clock_state() that gets called
via restore_processor_state() on x86, before calling
timekeeping_resume().