Re: [PATCH v4 1/8] xen/domain: introduce common emulation flags

[dmkhn@xxxxxxxxx]

On Wed, Aug 06, 2025 at 03:56:42PM +0200, Roger Pau Monné wrote:
> On Tue, Aug 05, 2025 at 12:54:31AM +0000, dmkhn@xxxxxxxxx wrote:
> > + Cc: Oleskii
> >
> > On Mon, Aug 04, 2025 at 11:46:36AM +0200, Jan Beulich wrote:
> > > On 31.07.2025 21:21, dmkhn@xxxxxxxxx wrote:
> > > > --- a/xen/include/xen/sched.h
> > > > +++ b/xen/include/xen/sched.h
> > > > @@ -652,6 +652,8 @@ struct domain
> > > >      unsigned int *llc_colors;
> > > >  #endif
> > > >
> > > > +    uint32_t emulation_flags;
> > >
> > > Just one further remark: The field probably never should have been of this
> > > type; unsigned int will do, and imo will want switching to while the field
> > > is being moved. (Before giving an x86 ack, I want to convince myself 
> > > though
> > > that this is moving us in the right direction.)
> >
> > Hi Jan,
> >
> > I can definitely use different mechanism for virt ns16550: add a new field 
> > in
> > xen_arch_domainconfig. That will also simplify some of the emulation_flags
> > checks on x86 and will be more flexible wrt emulator configuration (e.g. I 
> > can
> > allow passing I/O ports ranges).
> 
> For the time being, I would leave emulation_flags in
> xen_arch_domainconfig.

Ack; agreed.

>  The set of emulated devices is
> architecture-specific, and pulling it to the generic struct is IMO not
> specially helpful, as you then have the definition of the flags
> decoupled from the field definition.

NS16550 is not an arch-specific device though.
But yes, current implementation _is_ arch-specific.

> 
> For the emulated UART, I don't think you need a new field in
> xen_arch_domainconfig, just a new bit in emulation_flags? IOW:

I think new field is needed, since there are four legacy PC UART resource
sets selectable by the user. I'm dropping COM port build-time selection
and reworking it to be xl-configurable. That will be more flexible and
there will be less in-hypervisor changes.

> 
> #define _XEN_X86_EMU_VUART          11
> #define XEN_X86_EMU_VUART           (1U << _XEN_X86_EMU_VUART)
> 
> Thanks, Roger.