On 10/07/2010 07:14 PM, Gleb Natapov wrote:
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.
What about different pages, running the scheduler code?
Oh, and we'll run the scheduler recursively.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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