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Date:   Fri, 31 May 2019 16:31:56 +0200 (CEST)
From:   Jiri Kosina <jikos@kernel.org>
To:     Andy Lutomirski <luto@kernel.org>
cc:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        the arch/x86 maintainers <x86@kernel.org>,
        Pavel Machek <pavel@ucw.cz>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4] x86/power: Fix 'nosmt' vs. hibernation triple fault
 during resume
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On Fri, 31 May 2019, Andy Lutomirski wrote:

> 2. Put the CPU all the way to sleep by sending it an INIT IPI.
> 
> Version 2 seems very simple and robust.  Is there a reason we can't do
> it?  We obviously don't want to do it for normal offline because it
> might be a high-power state, but a cpu in the wait-for-SIPI state is
> not going to exit that state all by itself.
> 
> The patch to implement #2 should be short and sweet as long as we are
> careful to only put genuine APs to sleep like this.  The only downside
> I can see is that an new kernel resuming and old kernel that was
> booted with nosmt is going to waste power, but I don't think that's a
> showstopper.

Well, if *that* is not an issue, than the original 3-liner that just 
forces them to 'hlt' [1] would be good enough as well.

[1] https://lore.kernel.org/lkml/nycvar.YFH.7.76.1905291230130.1962@cbobk.fhfr.pm/

Thanks,

-- 
Jiri Kosina
SUSE Labs