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

[Wei Liu <wl@xxxxxxx>]

On Wed, Sep 25, 2019 at 01:02:50PM +0200, Roger Pau Monné wrote:
> On Mon, Sep 23, 2019 at 11:09:23AM +0100, Wei Liu wrote:
> > 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.
> 
> Thanks for doing this!
> 
> In the past I've played with trying to get Xen to boot as a guest on
> HyperV gen2 instances, and I did manage to get it booting, Linux
> however would get extremely confused because gen2 lacks emulated
> devices and instead the guest is forced to use the HyperV PV devices
> AFAIK.

How did you force Linux to use Hyper-V PV devices?  AIUI Linux won't
have access to VMBus (like XenBus but with some differences) and SynIC
(Synthetic interrupt controller, think of it as an abstraction around
event channel in Xen world) in the first place.  But I haven't tried
gen2 so I could be wrong.

> 
> Anyway, I had the following patch on my backlog which allowed me to
> boot on gen2 instances, posting it here in case it helps you if you
> plan to go that route.

The long term plan for the time source is to use the reference TSC page
provided by Hyper-V, just like we did for Xen.

Your patch seems to be an useful thing to do on its own anyway.

Wei.

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