Re: [PATCH v4] x86/power: Fix 'nosmt' vs. hibernation triple fault during resume

[Pavel Machek]

On Thu 2019-05-30 00:09:39, Jiri Kosina wrote:
> From: Jiri Kosina <jkosina@xxxxxxx>
> 
> As explained in
> 
> 	0cc3cd21657b ("cpu/hotplug: Boot HT siblings at least once")
> 
> we always, no matter what, have to bring up x86 HT siblings during boot at
> least once in order to avoid first MCE bringing the system to its knees.
> 
> That means that whenever 'nosmt' is supplied on the kernel command-line,
> all the HT siblings are as a result sitting in mwait or cpudile after
> going through the online-offline cycle at least once.
> 
> This causes a serious issue though when a kernel, which saw 'nosmt' on its
> commandline, is going to perform resume from hibernation: if the resume
> from the hibernated image is successful, cr3 is flipped in order to point
> to the address space of the kernel that is being resumed, which in turn
> means that all the HT siblings are all of a sudden mwaiting on address
> which is no longer valid.
> 
> That results in triple fault shortly after cr3 is switched, and machine
> reboots.
> 
> Fix this by always waking up all the SMT siblings before initiating the
> 'restore from hibernation' process; this guarantees that all the HT
> siblings will be properly carried over to the resumed kernel waiting in
> resume_play_dead(), and acted upon accordingly afterwards, based on the
> target kernel configuration.
> Symmetricaly, the resumed kernel has to push the SMT siblings to mwait
> again in case it has SMT disabled; this means it has to online all
> the siblings when resuming (so that they come out of hlt) and offline
> them again to let them reach mwait.
> 
> Cc: stable@xxxxxxxxxxxxxxx # v4.19+
> Debugged-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Fixes: 0cc3cd21657b ("cpu/hotplug: Boot HT siblings at least once")
> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>

Acked-by: Pavel Machek <pavel@xxxxxx>

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