Re: [PATCH] ns16550c: avoid crash in ns16550_endboot in PV shim mode

["Roger Pau Monné" <roger.pau@citrix.com>]

On Fri, Oct 20, 2023 at 02:25:35PM +0100, Andrew Cooper wrote:
> On 20/10/2023 11:29 am, David Woodhouse wrote:
> > On Fri, 2023-10-20 at 11:14 +0100, Andrew Cooper wrote:
> >> On 19/10/2023 5:21 pm, David Woodhouse wrote:
> >>> From: David Woodhouse <dwmw@amazon.co.uk>
> >>>
> >>> In shim mode there is no hardware_domain. Dereferencing the pointer
> >>> doesn't end well.
> >>>
> >>> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> >>> ---
> >>> This is about as far as I got in my abortive attempt to use the PV shim
> >>> without an actual PV console being provided by the HVM hosting
> >>> environment. It still doesn't pass the guest's console through to
> >>> serial; that only seems to shim to an actual PV console.
> >> There's no such thing as a Xen VM without a PV console.
> > Huh? There are literally millions of them.
> 
> I'm very prepared to believe there are millions which don't overtly
> malfunction when you don't fill in the HVM Params. 
> 
> Which is very different from saying "there's a way in the Xen guest ABI
> to express 'you don't have a PV console' ".

FWIW, Linux assumes that either the console page or the event channel
being 0 implies no console available [0], so I guess that's the ABI
now.

Roger.

[0] https://elixir.bootlin.com/linux/latest/source/drivers/tty/hvc/hvc_xen.c#L258