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Date:   Tue, 28 May 2019 21:22:14 +0200 (CEST)
From:   Jiri Kosina <jikos@kernel.org>
To:     Dongli Zhang <dongli.zhang@oracle.com>
cc:     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, 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.

That also explains why I apparently didn't see it that regularly with 
kaslr disabled.

Nothing to do with nvme, so let's not continue coming up with proper fix 
in this thread.

Thanks,

-- 
Jiri Kosina
SUSE Labs