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

[dmukhin@xen.org]

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@amd.com>

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@ford.com/

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?

What do you think?

> +#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
> 
>