On Wed, Apr 27, 2011 at 03:41:41PM +0300, Gleb Natapov wrote: > On Tue, Apr 26, 2011 at 08:55:28AM -0700, Paul E. McKenney wrote: > > On Tue, Apr 26, 2011 at 03:38:24PM +0300, Gleb Natapov wrote: > > > Hello Paul, > > > > > > I have a question about RCU + KVM. KVM does not hold any references to RCU > > > protected data when it switches CPU into a guest mode. In fact switching > > > to a guest mode is very similar to exiting to userspase from RCU point > > > of view. In addition CPU may stay in a guest mode for quite a long time > > > (up to one time slice). It looks like it will be beneficial to treat guest > > > mode as quiescent state, just like user-mode execution. How can this be > > > done? I was trying to find how RCU knows about cpu entering user-mode, > > > but it seems that it does this by checking CPU mode in a timer interrupt > > > (update_process_times()->rcu_check_callbacks()). This will not work for > > > guest mode detection since timer interrupt will kick CPU out of a guest > > > mode and timer interrupt will always see CPU in kernel mode. Do we have > > > a simple function to call to notify RCU that CPU passed quiescent state > > > which we can call just before entering guest? > > > > Hello, Gleb, > > > > You could call rcu_note_context_switch(), passing it the current > > CPU. Please note that preemption -must- be disabled when calling > > this. You could call this just after exiting the guest as well > > as just before entering guest. > > > x86 disable preemption and local interrupts before switching to guest > mode. Some platforms only disable local interrupts. I assume disabling > local irqs is as good as disabling preemption for rcu_note_context_switch() > calling purpose, is this correct? Yep, disabing hardirqs will suffice. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
