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

From: Wei Liu <wl@xen.org>
To: Paul Durrant <Paul.Durrant@citrix.com>
Cc: Wei Liu <liuwe@microsoft.com>, 'Wei Liu' <wl@xen.org>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	Michael Kelley <mikelley@microsoft.com>,
	Jan Beulich <jbeulich@suse.com>,
	Xen Development List <xen-devel@lists.xenproject.org>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH for-next RFC 0/8] Port Xen to Hyper-V
Date: Mon, 23 Sep 2019 15:21:23 +0100	[thread overview]
Message-ID: <20190923142123.h6c36wvmujghrhtm@debian> (raw)
In-Reply-To: <7266c9a91c7c4dcba0aab375fa5aad08@AMSPEX02CL03.citrite.net>

On Mon, Sep 23, 2019 at 01:47:14PM +0000, Paul Durrant wrote:
> > -----Original Message-----
> > From: Wei Liu <wl@xen.org>
> > Sent: 23 September 2019 14:34
> > To: Paul Durrant <Paul.Durrant@citrix.com>
> > Cc: 'Wei Liu' <wl@xen.org>; Xen Development List <xen-devel@lists.xenproject.org>; Wei Liu
> > <liuwe@microsoft.com>; Andrew Cooper <Andrew.Cooper3@citrix.com>; Michael Kelley
> > <mikelley@microsoft.com>; Jan Beulich <jbeulich@suse.com>; Roger Pau Monne <roger.pau@citrix.com>
> > 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.

Wei.

> 
>   Paul
> 
> > 
> > Wei.

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