Re: [Xen-devel] [RFC PATCH 00/16] xenhost support

[Ankur Arora]

On 2019-06-07 9:21 a.m., Juergen Gross wrote:
> On 07.06.19 17:22, Joao Martins wrote:
> > On 6/7/19 3:51 PM, Juergen Gross wrote:
> > > On 09.05.19 19:25, Ankur Arora wrote:
> > > > Hi all,
> > > >
> > > > This is an RFC for xenhost support, outlined here by Juergen here:
> > > > https://lkml.org/lkml/2019/4/8/67.
> > >
> > > First: thanks for all the effort you've put into this series!
> > >
> > > > The high level idea is to provide an abstraction of the Xen
> > > > communication interface, as a xenhost_t.
> > > >
> > > > xenhost_t expose ops for communication between the guest and Xen
> > > > (hypercall, cpuid, shared_info/vcpu_info, evtchn, grant-table and on 
> > > > top
> > > > of those, xenbus, ballooning), and these can differ based on the kind
> > > > of underlying Xen: regular, local, and nested.
> > >
> > > I'm not sure we need to abstract away hypercalls and cpuid. I believe in
> > > case of nested Xen all contacts to the L0 hypervisor should be done via
> > > the L1 hypervisor. So we might need to issue some kind of passthrough
> > > hypercall when e.g. granting a page to L0 dom0, but this should be
> > > handled via the grant abstraction (events should be similar).
> > Just to be clear: By "kind of passthrough hypercall" you mean (e.g. 
> > for every
> > access/modify of grant table frames) you would proxy hypercall to L0 
> > Xen via L1 Xen?
>
> It might be possible to spare some hypercalls by directly writing to
> grant frames mapped into L1 dom0, but in general you are right.
Wouldn't we still need map/unmap_grant_ref?
AFAICS, both the xenhost_direct and the xenhost_indirect cases should be
very similar (apart from the need to proxy in the indirect case.)

Ankur

> Juergen
>
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