linux-kernel - Re: [PATCH v2] x86/power: Fix 'nosmt' vs. hibernation triple fault during resume

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Message-ID: <nycvar.YFH.7.76.1905291921060.1962@cbobk.fhfr.pm>
Date:   Wed, 29 May 2019 19:29:49 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/power: Fix 'nosmt' vs. hibernation triple fault
 during resume

On Wed, 29 May 2019, Josh Poimboeuf wrote:

> I still have the question about whether we could make mwait_play_dead() 
> monitor a fixed address.  If we could get that to work, that seems more 
> robust to me.

Hmm, does it really?

That'd mean the resumer and resumee must have the same fixmap. How are you 
going to guarantee that? Currently the resuming kernel doesn't really have 
to be the same as the one that is being resumed.

> Another question.  With your patch, if booted with nosmt, is SMT still 
> disabled after you resume from hibernation?  

Yup, it is.

> I don't see how SMT would get disabled again.

The target kernel only onlines the CPUs which were online at the time of 
hibernation (and are therefore in frozen_cpus mask).

-- 
Jiri Kosina
SUSE Labs