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

[Jiri Kosina]

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