Linux Virtualization - Sep 2015 - rfc: vhost user enhancements for vm2vm communication

On Tue, Sep 01, 2015 at 05:01:07PM -0700, Nakajima, Jun
wrote:
> On Tue, Sep 1, 2015 at 9:28 AM, Jan Kiszka <jan.kiszka at
siemens.com> wrote:
> > On 2015-09-01 18:02, Michael S. Tsirkin wrote:
> ...
> >> You don't need to be able to map all guest memory if you know
> >> guest won't try to allow device access to all of it.
> >> It's a question of how good is the bus address allocator.
> >
> > But those BARs need to allocate a guest-physical address range as
large
> > as the other guest's RAM is, possibly even larger if that RAM is
not
> > contiguous, and you can't put other resources into potential holes
> > because VM2 does not know where those holes will be.
> >
> 
> I think you can allocate such guest-physical address ranges
> efficiently if each BAR sets the base of each memory region reported
> by VHOST_SET_MEM_TABLE, for example.  The issue is that we would need
> to 8 (VHOST_MEMORY_MAX_NREGIONS) of them vs. 6 (defined by PCI-SIG).
Besides, 8 is not even a limit: we merged a patch that allows makeing it
larger.
> -- 
> Jun
> Intel Open Source Technology Center

BTW, can you please take a look at the following URL to see my
understanding is correct? Our engineers are saying that they are not
really sure if they understood your proposal (especially around
IOMMU), and I drew a figure, adding notes...

https://wiki.opnfv.org/vm2vm_mst

Thanks,
-- 
Jun
Intel Open Source Technology Center

On Wed, Sep 02, 2015 at 09:45:45PM -0700, Nakajima, Jun
wrote:
> BTW, can you please take a look at the following URL to see my
> understanding is correct? Our engineers are saying that they are not
> really sure if they understood your proposal (especially around
> IOMMU), and I drew a figure, adding notes...
> 
> https://wiki.opnfv.org/vm2vm_mst
> 
> Thanks,
I think you got it right, thanks for putting this together!
> -- 
> Jun
> Intel Open Source Technology Center