Re: [PATCH 4/4] kvm,rcu: use RCU extended quiescent state when running KVM guest

[Rik van Riel <riel@redhat.com>]

On 02/05/2015 01:56 PM, Paul E. McKenney wrote:

> The real danger is doing neither.
> 
> On tick_nohz_full_cpu() CPUs, the exit-to-userspace code should invoke
> rcu_user_enter(), which sets some per-CPU state telling RCU to ignore
> that CPU, since it cannot possibly do host RCU read-side critical sections
> while running a guest.
> 
> In contrast, a non-tick_nohz_full_cpu() CPU doesn't let RCU
> know that it is executing in a guest or in userspace.  So the
> rcu_virt_note_context_switch() does the notification in that case.

Looking at context_tracking.h, I see the
function context_tracking_cpu_is_enabled().

That looks like it should do the right thing
in this case.