Re: Fwd: Inter-domain shared memory facility in Xen?

[Derek Murray <Derek.Murray@cl.cam.ac.uk>]

David Stone wrote:
> Thanks for your help on this.  So based on your responses I just want
> to confirm my understanding is correct...is it true that:
> 
> 1. It is currently possible to establish shared memory between Dom0
> and DomU, but
> 2. It is currently not possible to establish shared memory between two
> DomUs in an released Xen versions, nor the current xen-unstable branch
> nor any other branch on http://xenbits.xensource.org.  There are
> projects that address this that you mentioned though.

It *is* possible to establish shared memory between two DomUs, using the 
grant table mechanism. At present, it is only possible to grant access 
to memory from a VM kernel, but it is possible to map that granted 
memory into either the kernel (using the kernel wrappers to the 
necessary hypercalls) or user-space (using gntdev, the user-space 
granted memory driver).

Up to and including the current stable release (3.1.1), it is only 
possible for domains that have I/O memory permissions (typically only 
Dom0) to map granted pages. Therefore, it is necessary to give some 
dummy permissions to any domain that you want to allow to map grants. 
However, the issue that led to this restriction has been fixed in the 
current version of xen-unstable.

As I understand it, the other projects that were mentioned provide a 
socket-like communication mechanism for Xen, with the advantage that 
they do not (necessarily) use the networking stack. I presume that you 
are looking for something simpler, such as creating a shared data 
structure between two or more domains. In that case, the mechanisms that 
  exist in Xen today and that I have described above are sufficient for 
your needs.

Regards,

Derek Murray.