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. -- 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
