Messages in this thread | | | Date | Wed, 29 May 2019 11:10:28 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v2] x86/power: Fix 'nosmt' vs. hibernation triple fault during resume |
| |
On Wed, May 29, 2019 at 12:32:02PM +0200, Jiri Kosina wrote: > From: Jiri Kosina <jkosina@suse.cz> > > 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 which is no longer valid.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.
hibernation_restore() is called by user space at runtime, via ioctl or sysfs. So I think this still doesn't fix the case where you've disabled CPUs at runtime via sysfs, and then resumed from hibernation. Or are we declaring that this is not a supported scenario?
Would it be possible for mwait_play_dead() to instead just monitor a fixmap address which doesn't change for kaslr?
Is there are reason why maxcpus= doesn't do the CR4.MCE booted_once dance?
-- Josh
| |