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

[Wei Liu <wl@xxxxxxx>]

On Mon, Sep 23, 2019 at 02:39:10PM +0000, Paul Durrant wrote:
> > -----Original Message-----
> > From: Wei Liu <wl@xxxxxxx>
> > Sent: 23 September 2019 15:21
> > 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
> > 
> > On Mon, Sep 23, 2019 at 01:47:14PM +0000, Paul Durrant wrote:
> > > > -----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.
> > 
> > Oh, I was thinking more about names of Windows specific high-level
> > features. Yes I can definitely ask whether eVMCS is exposed to L2 Dom0 /
> > Root.
> 
> Oh, I see. The main ones are 'credential guard' and the more recent 'sandbox'.
> 

Got it.

Wei.

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