Re: [PATCH v10 5/5] xen: enable dom0less guests to use console_io hypercalls

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 4 Feb 2026, dmukhin@xxxxxxx wrote:
> On Wed, Feb 04, 2026 at 03:37:12PM -0800, Stefano Stabellini wrote:
> > Enable dom0less guests on ARM to use console_io hypercalls:
> > - set input_allow = true for dom0less domains
> > - update the in-code comment in console.c
> > - prioritize the VUART check to retain the same behavior as today
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> 
> The code looks good, just one remark wrt prioritizing VUART check.
> 
> > ---
> >  xen/common/device-tree/dom0less-build.c |  2 ++
> >  xen/drivers/char/console.c              | 16 ++++++++++------
> >  2 files changed, 12 insertions(+), 6 deletions(-)
> > 
> > diff --git a/xen/common/device-tree/dom0less-build.c 
> > b/xen/common/device-tree/dom0less-build.c
> > index 840d14419d..cb7026fa7e 100644
> > --- a/xen/common/device-tree/dom0less-build.c
> > +++ b/xen/common/device-tree/dom0less-build.c
> > @@ -829,6 +829,8 @@ static int __init construct_domU(struct kernel_info 
> > *kinfo,
> >  
> >      rangeset_destroy(kinfo->xen_reg_assigned);
> >  
> > +    d->console->input_allowed = true;
> > +
> >      return rc;
> >  }
> >  
> > diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> > index d3ce925131..7f0c3d8376 100644
> > --- a/xen/drivers/char/console.c
> > +++ b/xen/drivers/char/console.c
> > @@ -610,11 +610,20 @@ static void __serial_rx(char c)
> >      if ( ACCESS_ONCE(console_rx) == 0 )
> >          return handle_keypress(c, false);
> >  
> > +    /* Includes an is_focus_domain() check. */
> >      d = console_get_domain();
> >      if ( !d )
> >          return;
> >  
> > -    if ( is_hardware_domain(d) )
> 
> Hardware domain on x86 may have an emulated UART (not in upstream, through,
> I need to send v8 for NS16550 series...). The patch which illustrates the
> idea:
>    https://lore.kernel.org/xen-devel/20250908211149.279143-2-dmukhin@xxxxxxxx/
> 
> So this code (hopefully soon) will need adjustment again.
>
> I would update the code to something like:
> 
> 
> 
>     if ( is_hardware_domain(d) && !domain_has_vuart(d) )
>     {
>         // handle hardware domain
>     }
> #ifdef CONFIG_SBSA_VUART_CONSOLE
>     else if ( domain_has_vuart(d) )
>         /* Deliver input to the emulated UART. */
>         rc = vpl011_rx_char_xen(d, c);
> #endif
> 
> 
> 
> But domain_has_vuart() needs to be defined for all architectures
> (currently it is hidden in arch/arm/vuart.c).
> 
> Or perhaps it is possible to postpone the change?

This change is needed to avoid regressions on ARM.

However, while I wouldn't be surprised if we need a change here for your
upcoming patch series, at the same time at the moment I don't see why
this check wouldn't work as it is for you as well.

On x86, CONFIG_SBSA_VUART_CONSOLE will never be set. It is OK to do this
first:

#ifdef CONFIG_SBSA_VUART_CONSOLE
    /* Prioritize vpl011 if enabled for this domain */
    if ( d->arch.vpl011.base_addr )
    {
        /* Deliver input to the emulated UART. */
        rc = vpl011_rx_char_xen(d, c);
    }
    else
#endif

It shouldn't hurt. The is_hardware_domain() check is also not necessary
anymore because any necessary check would be part of this check above: 

      d = console_get_domain();
      if ( !d )
          return;

So I am guessing that your series might actually leave this code
unchanged and instead might modify console_get_domain() or
max_console_rx.



> > +#ifdef CONFIG_SBSA_VUART_CONSOLE
> > +    /* Prioritize vpl011 if enabled for this domain */
> > +    if ( d->arch.vpl011.base_addr )
> > +    {
> > +        /* Deliver input to the emulated UART. */
> > +        rc = vpl011_rx_char_xen(d, c);
> > +    }
> > +    else
> > +#endif
> >      {
> >          unsigned long flags;
> >  
> > @@ -633,11 +642,6 @@ static void __serial_rx(char c)
> >           */
> >          send_guest_domain_virq(d, VIRQ_CONSOLE);
> >      }
> > -#ifdef CONFIG_SBSA_VUART_CONSOLE
> > -    else
> > -        /* Deliver input to the emulated UART. */
> > -        rc = vpl011_rx_char_xen(d, c);
> > -#endif
> >  
> >      if ( consoled_is_enabled() )
> >          /* Deliver input to the PV shim console. */
> > -- 
> > 2.25.1
> > 
> > 
>