linux-kernel - Re: [PATCH v4] x86/power: Fix 'nosmt' vs. hibernation triple fault during resume

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Date:   Fri, 31 May 2019 16:33:51 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Pavel Machek <pavel@....cz>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] x86/power: Fix 'nosmt' vs. hibernation triple fault
 during resume

On Fri, 31 May 2019, Jiri Kosina wrote:

> 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.

Actually no, scratch that, I misunderstood your proposal, sorry.

-- 
Jiri Kosina
SUSE Labs