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Date:   Wed, 29 May 2019 10:56:18 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Jiri Kosina <jikos@kernel.org>
Cc:     Dongli Zhang <dongli.zhang@oracle.com>,
        Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Sagi Grimberg <sagi@grimberg.me>, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org,
        Keith Busch <keith.busch@intel.com>,
        Hannes Reinecke <hare@suse.de>, Christoph Hellwig <hch@lst.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>, linux-pm@vger.kernel.org,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: "nosmt" breaks resuming from hibernation (was Re: [5.2-rc1
 regression]: nvme vs. hibernation)
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On Tue, May 28, 2019 at 09:22:14PM +0200, Jiri Kosina wrote:
> On Tue, 28 May 2019, Jiri Kosina wrote:
> 
> > [ some x86/PM folks added ]
> > 
> > I isolated this to 'nosmt' being present in the "outer" (resuming) kernel, 
> > and am still not sure whether this is x86 issue or nvme/PCI/blk-mq issue.
> > 
> > For the newcomers to this thread: on my thinkpad x270, 'nosmt' reliably 
> > breaks resume from hibernation; after the image is read out from disk and 
> > attempt is made to jump to the old kernel, machine reboots.

> 
> Thomas figured it out (and this should be really more widespread than just 
> my machine :) ).
> 
> nosmt forces HT siblings to mwait, but that explodes after %cr3 change 
> during resume, as the mwait target address is all of a sudden not valid 
> anymore for neither of the hyperthreads.

ARGH!!! But also, you wrote:

> > I verified that it succesfully makes it to the point where restore_image()
> > is called from swsusp_arch_resume() (and verified that only BSP is alive
> > at that time), but the old kernel never comes back and triplefault-like
> > reboot happens.

which means that even without nosmt all 'other' CPUs are offline. And
when I look at resume_target_kernel() I see it call
hibernate_resume_nonboot_cpu_disable().

So how is the SMT offline different from that offline? afaict they all
get into play_dead()->native_play_dead()->mwait_play_dead().