Re: [PATCH v2 05/12] Handle asynchronous page fault in a PV guest.

Avi Kivity
2009-11-25T12:45:40Z

On 11/23/2009 04:06 PM, Gleb Natapov wrote:
> Asynchronous page fault notifies vcpu that page it is trying to access
> is swapped out by a host. In response guest puts a task that caused the
> fault to sleep until page is swapped in again. When missing page is
> brought back into the memory guest is notified and task resumes execution.
>
> +
> +static void apf_task_wait(struct task_struct *tsk, u32 token)
> +{
> + u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS);
> + struct kvm_task_sleep_head *b =&async_pf_sleepers[key];
> + struct kvm_task_sleep_node n, *e;
> + DEFINE_WAIT(wait);
> +
> + spin_lock(&b->lock);
> + e = _find_apf_task(b, token);
> + if (e) {
> + /* dummy entry exist -> wake up was delivered ahead of PF */
> + hlist_del(&e->link);
> + kfree(e);
> + spin_unlock(&b->lock);
> + return;
> + }
> +
> + n.token = token;
> + init_waitqueue_head(&n.wq);
> + hlist_add_head(&n.link,&b->list);
> + spin_unlock(&b->lock);
> +
> + for (;;) {
> + prepare_to_wait(&n.wq,&wait, TASK_UNINTERRUPTIBLE);
> + if (hlist_unhashed(&n.link))
> + break;
>

This looks safe without b->lock, but please add a comment explaining why
it is safe.

> +int kvm_handle_pf(struct pt_regs *regs, unsigned long error_code)
> +{
> + u32 reason, token;
> +
> + if (!per_cpu(apf_reason, smp_processor_id()).enabled)
> + return 0;
> +
> + reason = per_cpu(apf_reason, smp_processor_id()).reason;
> + per_cpu(apf_reason, smp_processor_id()).reason = 0;
>

Use __get_cpu_var(), shorter.

> @@ -270,11 +399,14 @@ static void __init kvm_smp_prepare_boot_cpu(void)
>
> void __init kvm_guest_init(void)
> {
> + int i;
>

\n

> if (!kvm_para_available())
> return;
>
> paravirt_ops_setup();
> register_reboot_notifier(&kvm_pv_reboot_nb);
> + for (i = 0; i< KVM_TASK_SLEEP_HASHSIZE; i++)
> + spin_lock_init(&async_pf_sleepers[i].lock);
> #ifdef CONFIG_SMP
> smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
> #else
>

--
error compiling committee.c: too many arguments to function