Re: [PATCH][RFC] x86, hotplug: Use zero page for monitor when resuming from hibernation

[Brian Gerst]

On Mon, Jun 6, 2016 at 12:40 PM, Peter Zijlstra <pet...@infradead.org> wrote:
> On Mon, Jun 06, 2016 at 03:59:06PM +0000, Chen, Yu C wrote:
>
>> > > + if (hibernation_in_resume())
>> > > +         mwait_ptr = empty_zero_page;
>> > > + else
>> > > +         mwait_ptr = &current_thread_info()->flags;
>> >
>> > Why is this conditional? Is there any case in which the zero page is not 
>> > also
>> > correct?
>> I'm thinking of avoid unnecessary wakeup for normal CPU offline,  for 
>> example,
>> if one  driver uses  the zero page and access it.
>
> Writing to the zero page would be a major fail.

I would think the safest thing to do during resume from hibernation is
to use hlt instead of mwait, so there is no dependency on any memory
address.  It doesn't need the power management features of mwait
either because the CPU will be reset soon after the restored kernel
resumes.

--
Brian Gerst