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

[Peter Xu]

On Thu, Aug 24, 2017 at 08:27:23PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
> 
> **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?

-- 
Peter Xu