Re: [RFC] VMI for Xen?

[Anthony Liguori <aliguori@us.ibm.com>]

Ian Pratt wrote:
>> Just some food for thought,  I did a simple analysis of the 
>> size of Xen Linux patches verses the VMI patches.  To make 
>> things more fair, I removed everything from the XenoLinux 
>> port accept for the i386 xen subarch (so no drivers and no 
>> support for other architectures).
>>     
>
> Your analysis is still taking all the patches to make dom0 functionality
> work, which accounts for a lot of changes and is totally outside of the
> scope of VMI.
>
> We've been working with a bunch of RH/Novell folks to create a stripped
> down domU-only Xen patch that would be a fairer comparison.
>
> We're currently looking though the new VMI patchset to see whether
> there's anything worth having, in particular, if there's anything that
> should be added to our patch to support what we can deduce that their
> hypervisor probably needs. We've also talking to the VirtualIron team to
> make sure we're inclusive as possible.
>
> The current VMI patchset couldn't support Xen's direct-mode (non shadow)
> MMU virtualization, and hasn't really been thought through properly for
> SMP. I'm sure we'll get something worked out that keeps everyone happy.
>   
Actually, the new spec does support non-shadow paging.  All page table 
updates are done via the VMI ROM.  Normally, these are just normal 
get/set operations but they could be get/sets with p2m looks.  The first 
version of the spec definitely didn't support non-shadow paging though.

We'll see whether it's actually implementable when the wedge is released 
though.  I wouldn't be surprised if they are using shadow paging.

The new spec does actually introduce SMP stuff but yeah, you're probably 
right, it may not have been thought through enough...  The biggest gaps 
that I can find appear to be DMA support and event channels.  I think to 
properly support event channel you need a bit more pervasive changes.  I 
think DMA is a pretty simply change (you just have to update the DMA bus 
translation functions to do a p2m lookup).

Regards,

Anthony Liguori
> Ian
>