Re: [PATCH 12/12] hw/xen: add support for Xen primary console in emulated mode

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 24/10/2023 16:49, David Woodhouse wrote:
> On Tue, 2023-10-24 at 16:39 +0100, Paul Durrant wrote:
> > On 24/10/2023 16:37, David Woodhouse wrote:
> > > On Tue, 2023-10-24 at 15:20 +0100, Paul Durrant wrote:
> > > > On 16/10/2023 16:19, David Woodhouse wrote:
> > > > > From: David Woodhouse <dwmw@xxxxxxxxxxxx>
> > > > >
> > > > > The primary console is special because the toolstack maps a page at a
> > > > > fixed GFN and also allocates the guest-side event channel. Add support
> > > > > for that in emulated mode, so that we can have a primary console.
> > > > >
> > > > > Add a *very* rudimentary stub of foriegnmem ops for emulated mode, which
> > > > > supports literally nothing except a single-page mapping of the console
> > > > > page. This might as well have been a hack in the xen_console driver, but
> > > > > this way at least the special-casing is kept within the Xen emulation
> > > > > code, and it gives us a hook for a more complete implementation if/when
> > > > > we ever do need one.
> > > > Why can't you map the console page via the grant table like the xenstore
> > > > page?
> > > I suppose we could, but I didn't really want the generic xen-console
> > > device code having any more of a special case for 'Xen emulation' than
> > > it does already by having to call xen_primary_console_create().
> > But doesn't is save you the whole foreignmem thing? You can use the
> > grant table for primary and secondary consoles.
> Yes. And I could leave the existing foreignmem thing just for the case
> of primary console under true Xen. It's probably not that awful a
> special case, in the end.
>
> Then again, I was surprised I didn't *already* have a foreignmem ops
> for the emulated case, and we're probably going to want to continue
> fleshing it out later, so I don't really mind adding it.
True. We'll need it for some of the other more fun protocols like vkbd 
or fb. Still, I think it'd be nicer to align the xenstore and primary 
console code to look similar and punt the work until then :-)
  Paul