Re: [PATCH v1 5/5] i386: Hyper-V VMBus ACPI DSDT entry

[Roman Kagan <rvkagan@yandex-team.ru>]

On Thu, Apr 09, 2020 at 06:35:18AM +0300, Jon Doron wrote:
> On 08/04/2020, Roman Kagan wrote:
> > On Wed, Apr 08, 2020 at 07:16:39AM +0300, Jon Doron wrote:
> > > Well I have implemented the hyperv synthetic kernel debugger interface, but
> > > on Windows 10 it requires to have a working VMBus (it's not really using it,
> > > but without a function vmbus that will answer to the initiate contact then
> > > the kdnet will simply be stuck in a loop.

I tried to google for this interface but the only thing I managed to
find was this

https://withinrafael.com/2015/02/01/how-to-set-up-synthetic-kernel-debugging-for-hyper-v-virtual-machines/

Is this what you're trying to implement?  Are there any more
authoritative descriptions of the feature?

The document doesn't quite explain the inner workings of the feature,
but it looks like the regular network debugging interface, except that
IP is forwarded by the hypervisor app, so that the debugger has to
connect to the host and avoid setting up full-fledged network
connectivity to the guest.  That would be essentially hv-net + slirp.
OTOH you say it doesn't use VMBus so I'm confused...

Thanks,
Roman.

> > > In addition to that Michael Kelley from Microsoft has informed us that
> > > Microsoft might be dropped the synthetic kernel debugger interface sometime
> > > in the future, and it seems like the new mode is simply to use hvnet device
> > > for the communication (which is again much faster).