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SubjectRe: [PATCH v6 08/12] Handle async PF in a guest.
  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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