Re: [PATCH] mem_event: use wait queue when ring is full

[Olaf Hering <olaf@aepfle.de>]

On Mon, Dec 05, Andres Lagar-Cavilla wrote:

> > On Mon, Dec 05, Andres Lagar-Cavilla wrote:
> >
> >> > +    med->bit = bit;
> >> I think it's been asked before for this to have a more expressive name.
> >
> > I have to recheck, AFAIK it was the mem_bit where mem_ is redundant.
> how about pause_flag?

I made this change in my patch.

> > Before this patch, mem_event_unpause_vcpus() was used to resume waiters
> > for the ring itself and for room in the ring.
> > Now there is mem_event_wake_waiters(), which indicates the ring is
> > active, and there is mem_event_wake_requesters() which indicates the
> > ring has room to place guest requests.
> 
> I think that if there is no ring where one is expected, harsher actions
> should happen. That is what we do in our patch. e.g.
> p2m_mem_paging_populate -> no ring -> crash domain, or
> p2m_mem_access_check -> access_required -> no ring -> crash domain.
> 
> That would eliminate wake_waiters, methinks?

In p2m_mem_paging_populate() a sanity check could be added. I think it
would indicate bad p2mt state because nominate was called without ring.
How else can a gfn enter paging state?

Olaf