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 12:27
> 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 10:48:45AM +0000, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Wei 
> > > Liu
> > > Sent: 23 September 2019 11:09
> > > To: Xen Development List <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> > > Cc: Wei Liu <liuwe@xxxxxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>;
> > > Michael Kelley <mikelley@xxxxxxxxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; 
> > > Roger Pau Monne
> > > <roger.pau@xxxxxxxxxx>
> > > Subject: [Xen-devel] [PATCH for-next RFC 0/8] Port Xen to Hyper-V
> > >
> > > Hi all
> > >
> > > In case you're wondering, I can already run a fully fledged Xen system on
> > > Hyper-V with emulated disk and network.
> > >
> > > This is the very first stage for porting Xen to run on Hyper-V with all 
> > > the
> > > goodies Hyper-V has to offer.  With this series, Xen can successfully 
> > > detect
> > > Hyper-V and prints out a message.  I would like to first get the directory
> > > structure and kconfig options agreed upon.
> > >
> > > There are two major areas to be worked on:
> > >   * Make Dom0 able to use Hyper-V's synthetic devices.
> > >   * Make Xen use of the synthetic timer, reference TSC and enlightenment 
> > > VMCS
> > >     and other interfaces.
> > >
> > > They aren't trivial, and time can be scarce on my side, so I intend to 
> > > post
> > > patches piece meal when they are ready.
> > >
> > > Questions and comments are welcome.
> >
> > Yay! Glad you found the time to do this :-) Making use of the synic,
> > stimer, will be useful. To get the benefit for nested guests though, I
> > assume we'll need to exposed enlightened VMCS, EPT flush, etc.
> > through?
> 
> 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.

> There are hypercalls for virtual TLB management. We may choose to expose
> them to L2 guests for better performance.
> 

Do you mean 'Direct Virtual Flush'? The hypercalls in question are already 
handled in viridian for the purposes of remote TLB flush, so I guess it would 
be a question of wiring them through.

  Paul

> Wei.

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