On Thu, Oct 07, 2010 at 03:10:27PM +0200, Avi Kivity wrote:
> On 10/04/2010 05:56 PM, Gleb Natapov wrote:
> >When async PF capability is detected hook up special page fault handler
> >that will handle async page fault events and bypass other page faults to
> >regular page fault handler. Also add async PF handling to nested SVM
> >emulation. Async PF always generates exit to L1 where vcpu thread will
> >be scheduled out until page is available.
> >
>
> Please separate guest and host changes.
>
> >+void kvm_async_pf_task_wait(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;
> >+ n.cpu = smp_processor_id();
> >+ 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;
> >+ local_irq_enable();
>
> Suppose we take another apf here. And another, and another (for
> different pages, while executing schedule()). What's to prevent
> kernel stack overflow?
>
Host side keeps track of outstanding apfs and will not send apf for the
same phys address twice. It will halt vcpu instead.
> >+ schedule();
> >+ local_irq_disable();
> >+ }
> >+ finish_wait(&n.wq,&wait);
> >+
> >+ return;
> >+}
> >+EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait);
> >+
> I have a truly marvellous patch that fixes the bug which this
> signature is too narrow to contain.
--
Gleb.
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