Re: [patch V4 part 1 12/36] x86/kvm: Sanitize kvm_async_pf_task_wait()

[Thomas Gleixner]

"Paul E. McKenney" <paulmck@xxxxxxxxxx> writes:
> On Tue, May 05, 2020 at 03:16:14PM +0200, Thomas Gleixner wrote:
>> RCU is watching for:
>> 
>>   #1  The vCPU exited and current is definitely not the idle task
>> 
>>   #2a The #PF entry code on the guest went through enter_from_user_mode()
>>       which reactivates RCU
>
> I have to double-check...  The NO_HZ_FULL case transitioning to/from
> userspace is entirely non-preemptible, correct?  (After rcu_user_enter()
> and before rcu_user_exit(), respectively.)

Yes. It runs with interrupts disabled down to the actual return (sysret,
iret).

Thanks,

        tglx