linux-kernel - Re: "nosmt" breaks resuming from hibernation (was Re: [5.2-rc1 regression]: nvme vs. hibernation)

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Message-ID: <nycvar.YFH.7.76.1905282118070.1962@cbobk.fhfr.pm>
Date:   Tue, 28 May 2019 21:22:14 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Dongli Zhang <dongli.zhang@...cle.com>
cc:     Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Sagi Grimberg <sagi@...mberg.me>, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org,
        Keith Busch <keith.busch@...el.com>,
        Hannes Reinecke <hare@...e.de>, Christoph Hellwig <hch@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: "nosmt" breaks resuming from hibernation (was Re: [5.2-rc1
 regression]: nvme vs. hibernation)

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