Re: [Xen-devel] [PATCH for-next RFC 0/8] Port Xen to Hyper-V

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu <wl@xxxxxxx>
> Sent: 23 September 2019 14:34
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: 'Wei Liu' <wl@xxxxxxx>; Xen Development List 
> <xen-devel@xxxxxxxxxxxxxxxxxxxx>; Wei Liu
> <liuwe@xxxxxxxxxxxxx>; Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Michael 
> Kelley
> <mikelley@xxxxxxxxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Roger Pau Monne 
> <roger.pau@xxxxxxxxxx>
> Subject: Re: [Xen-devel] [PATCH for-next RFC 0/8] Port Xen to Hyper-V
> 
> And a bit more thought.
> 
> On Mon, Sep 23, 2019 at 01:54:31PM +0100, Wei Liu wrote:
> [...]
> > > >
> > > > Per TLFS, eVMCS should be used by L1 Xen.
> > >
> > > Yes, I guess it only needs to be used by L1, but Windows is using an
> > > increasing number of VMs for various purposes so I think making it
> > > stack well would be useful.
> > >
> > > >
> > > > Not sure what you meant by EPT flush. If you mean things like
> > > > HvFlushGuestPhysicalAddressSpace, I think they should be used by Xen
> > > > only as well. I'm not sure whether they should be expose to L2 guests.
> > > >
> > >
> > > Yes, that's what I meant and, again, I was thinking about the nested
> > > Windows guest using VMs itself.
> >
> > So this is basically nested on nested. I'm not sure how to make that
> > work yet.  I'm also not sure how well these interfaces stack. TLFS only
> > describes one level of nesting. I will need to ask if we can make nested
> > on nested work.
> >
> 
> Since L2 Root is Windows in a Hyper-V setup, chances are what you want
> already works. Of course this depends on whether Windows, when running
> as Root or Child, uses VM related features.
> 
> I'm not versed in Windows features. If you have specific things in mind,
> I can ask for more details and think about how to implement them in Xen.

Well, eVMCS would be a major one. If the L2 Windows could be told to use that 
rather than L0 have to bounce individual VMREAD/VMWRITEs up to L1 then that 
would be a win.

  Paul

> 
> Wei.

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