Re: [Xen-devel] address mapping between domains

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

> Right now only privileged domains (i.e. dom0 or a driver domain) can map
> the memory of other domains.  Sharing will be more flexible once the grant
> tables work is done and the reverse operation will be possible.
>
> Perhaps for your shared memory work you could initially test with sharing
> between dom0 and a single domU?  Then you can move to grant tables when
> they're ready to perform arbitrary sharing?

Another thing you could do as a workaround is make all the domains you're 
interested in into privileged domains.  Right now this means making them into 
driver domains* - you could give them all access to a spare PCI device on 
your system but not compile the driver into their kernels so they won't try 
to drive it.  Once you do this, they can map any other domain's memory.

[*] this is a hack - it'd be nice if it were possible to just make domains 
privileged but there's currently not there corresponding path in the tools.

Cheers,
Mark

>
> Cheers,
> Mark
>
> > > > Another question is about the hypercall: update_va_mapping. It has
> > > > three arguments: vaddr, val, flags. Can anyone kindly explain the
> > > > meaning of them and how they are used in the hypercall? Actually I am
> > > > puzzled why there is no machine page id as an argument, since the
> > > > virtual address should be mapped to a machine page anyway when the
> > > > page table is updated.
> > >
> > > Arguments to this as as Chris described.
> > >
> > > Note that the backend drivers often use a "multicall" to perfrom
> > > multiple operations (e.g. update multiple address mappings) in one
> > > hypercall.
> >
> > Yes, I have noticed it. Thanks a lot for help.
> >
> > --------------------------
> > Zhiyi from EPFL Switzerland


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