Re: [Qemu-devel] [RFC v2 25/32] vhost+postcopy: Lock around set_mem_table

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> On Thu, Aug 24, 2017 at 08:27:23PM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > **HACK - better solution needed **
> > We have the situation where:
> > 
> >      qemu                      bridge
> > 
> >      send set_mem_table
> >                               map memory
> >   a)                          mark area with UFD
> >                               send reply with map addresses
> >   b)                          start using
> >   c) receive reply
> > 
> >   As soon as (a) happens qemu might start seeing faults
> > from memory accesses (but doesn't until b); but it can't
> > process those faults until (c) when it's received the
> > mmap addresses.
> > 
> > Make the fault handler spin until it gets the reply in (c).
> > 
> > At the very least this needs some proper locks, but preferably
> > we need to split the message.
> 
> I see discussions about slave channel and ack mechanism in previous
> post.  So it's still not adopted (which looks doable)?  What's our
> further plan?

Yep I'm going to look at the slave channel stuff.

Dave

> -- 
> Peter Xu
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK