On Tue, Nov 27, 2012 at 07:12:40PM +0100, Frederic Weisbecker wrote: > 2012/11/27 Gleb Natapov <gleb@xxxxxxxxxx>: > > On Tue, Nov 27, 2012 at 06:30:32PM +0100, Frederic Weisbecker wrote: > >> 2012/11/27 Gleb Natapov <gleb@xxxxxxxxxx>: > >> > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > >> > index 4180a87..636800d 100644 > >> > --- a/arch/x86/kernel/kvm.c > >> > +++ b/arch/x86/kernel/kvm.c > >> > @@ -113,7 +113,7 @@ void kvm_async_pf_task_wait(u32 token) > >> > int cpu, idle; > >> > > >> > cpu = get_cpu(); > >> > - idle = idle_cpu(cpu); > >> > + idle = is_idle_task(current); > >> > >> I suggest this part goes to a standalone patch. > >> > >> > put_cpu(); > >> > > >> > spin_lock(&b->lock); > >> > @@ -247,10 +247,7 @@ do_async_page_fault(struct pt_regs *regs, unsigned long error_code) > >> > break; > >> > case KVM_PV_REASON_PAGE_NOT_PRESENT: > >> > /* page is swapped out by the host. */ > >> > - rcu_irq_enter(); > >> > - exit_idle(); > >> > kvm_async_pf_task_wait((u32)read_cr2()); > >> > - rcu_irq_exit(); > >> > >> Hmm, we still need those above around. I believe we just need to add > >> rcu_user_exit() in the beginning of that case. > > The exception may happen in kernel space too. Is calling rcu_user_exit() > > still OK? Also why calling exit_idle() if we are not exiting idle? > > Yeah, rcu_user_exit() takes care of that. And exit_idle() also checks > we are really idle before firing the notifier. > > Now we should probably call back enter_idle() before resuming idle if > needed. We disable irqs before calling enter_idle(). And exit_idle() > is called from irqs. This way we ensure it's either called before we > called local_irq_disable() or while the CPU is halt(). This provides > the guarantee that enter_idle() is always called before the CPU goes > to sleep. The fact we call exit_idle() from an exception in idle > breaks this guarantee. But that's another issue. What is the semantics of enter_idle()/exit_idle(), what are they used for? Not present fault happening in idle task does not mean we exit idle task. If this happens exception handler will execute sti; hlt waiting for missing page to be ready. Any interrupt happening during this hlt will do exit_idle() by itself. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
