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

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Date:   Fri, 31 May 2019 10:26:26 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "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, May 31, 2019 at 04:54:20PM +0200, Jiri Kosina wrote:
> On Fri, 31 May 2019, Andy Lutomirski wrote:
> 
> > For that matter, what actually happens if we get an SMI while halted?  
> > Does RSM go directly to sleep or does it re-fetch the HLT?
> 
> Our mails just crossed, I replied to Josh's mwait() proposal patch a 
> minute ago.

Good catch.  I agree that mwait seems unsafe across resume and my patch
is bogus.

Andy, in the short term it sounds like you're proposing to make
native_play_dead() use hlt_play_dead() unconditionally.  Right?

That would simplify things and also would fix Jiri's bug I think.  The
only question I'd have is if we have data on the power savings
difference between hlt and mwait.  mwait seems to wake up on a lot of
different conditions which might negate its deeper sleep state.

Andy, for your long term idea to use INIT IPI, I wonder if that would
work with SMT siblings?  Specifically I wonder about the Intel issue
that requires siblings to have CR4.MCE set.

-- 
Josh