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

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Message-ID: <nycvar.YFH.7.76.1905291818470.1962@cbobk.fhfr.pm>
Date:   Wed, 29 May 2019 18:26:59 +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:

> hibernation_restore() is called by user space at runtime, via ioctl or 
> sysfs.  So I think this still doesn't fix the case where you've disabled 
> CPUs at runtime via sysfs, and then resumed from hibernation.  Or are we 
> declaring that this is not a supported scenario?

Yeah I personally find that scenario awkward :) Anyway, cpuhp_smt_enable() 
is going to online even those potentially "manually" offlined CPUs, isn't 
it?

Are you perhaps suggesting to call enable_nonboot_cpus() instead of 
cpuhp_smt_enable() here to make it more explicit?

> Is there are reason why maxcpus= doesn't do the CR4.MCE booted_once
> dance?

I am not sure whether it's really needed. My understanding is that the MCE 
issue happens only after primary sibling has been brought up; if that 
never happened, MCE wouldn't be broadcasted to that core at all in the 
first place.

But this needs to be confirmed by Intel.

-- 
Jiri Kosina
SUSE Labs