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Date:   Fri, 31 May 2019 10:47:21 +0200 (CEST)
From:   Jiri Kosina <jikos@kernel.org>
To:     Josh Poimboeuf <jpoimboe@redhat.com>
cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        the arch/x86 maintainers <x86@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        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>,
        Andy Lutomirski <luto@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, Josh Poimboeuf wrote:

> > I disagree with that from the backwards compatibility point of view.
> > 
> > I personally am quite frequently using differnet combinations of 
> > resumer/resumee kernels, and I've never been biten by it so far. I'd guess 
> > I am not the only one.
> > Fixmap sort of breaks that invariant.
> 
> Right now there is no backwards compatibility because nosmt resume is
> already broken.

Yeah, well, but that's "only" for nosmt kernels at least.

> For "future" backwards compatibility we could just define a hard-coded 
> reserved fixmap page address, adjacent to the vsyscall reserved address.
> 
> Something like this (not yet tested)?  Maybe we could also remove the
> resume_play_dead() hack?

Does it also solve cpuidle case? I have no overview what all the cpuidle 
drivers might be potentially doing in their ->enter_dead() callbacks. 
Rafael?

Thanks,

-- 
Jiri Kosina
SUSE Labs