Re: [PATCH v4 8/8] emul/vuart: introduce console forwarding enforcement via vUART

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 31 Jul 2025, dmkhn@xxxxxxxxx wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx> 
> 
> It may be useful to enforce console forwarding over the virtual UART. E.g.
> hardware domain uses PV console by default, but it may be necessary to have
> console forwarded to the hardware domain via emulated UART.
> 
> Add CONFIG_VUART_CONSOLE_FOCUS to enforce such behavior.
> 
> Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>

I realize that hyperlaunch is not merged yet, but I think this one would
be best as a hyperlaunch configuration option rather than a kconfig. But
it is certainly useful for testing until Hyperlaunch is merged!


> ---
> Changes since v3:
> - new patch
> ---
>  xen/arch/x86/domain.c         | 6 ++++++
>  xen/common/emul/vuart/Kconfig | 5 +++++
>  xen/drivers/char/console.c    | 2 +-
>  3 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
> index 39b0c0b199b9..40ff92ad6c61 100644
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -848,6 +848,12 @@ int arch_domain_create(struct domain *d,
>      if ( is_hardware_domain(d) && is_pv_domain(d) )
>          emflags |= XEN_X86_EMU_PIT;
>  
> +    if ( IS_ENABLED(CONFIG_VUART_CONSOLE_FOCUS) &&
> +         IS_ENABLED(CONFIG_VUART_NS16550) &&
> +         is_hardware_domain(d) &&
> +         is_hvm_domain(d) )
> +        emflags |= XEN_X86_EMU_NS16550;
> +
>      if ( emflags & ~XEN_X86_EMU_ALL )
>      {
>          printk(XENLOG_G_ERR
> diff --git a/xen/common/emul/vuart/Kconfig b/xen/common/emul/vuart/Kconfig
> index ebefd90d913e..1069ca95f2db 100644
> --- a/xen/common/emul/vuart/Kconfig
> +++ b/xen/common/emul/vuart/Kconfig
> @@ -51,4 +51,9 @@ config VUART_NS16550_DEBUG
>       help
>         Enable development debugging.
>  
> +config VUART_CONSOLE_FOCUS
> +     bool "Console input forwarding via UART emulator"
> +     help
> +       Enable physical console input forwarding to guest OS via emulated 
> UART.
> +
>  endmenu
> diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> index 93254979817b..d142f5511d61 100644
> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -597,7 +597,7 @@ static void __serial_rx(char c)
>      if ( !d )
>          return;
>  
> -    if ( is_hardware_domain(d) )
> +    if ( !IS_ENABLED(CONFIG_VUART_CONSOLE_FOCUS) && is_hardware_domain(d) )
>      {
>          /*
>           * Deliver input to the hardware domain buffer, unless it is
> -- 
> 2.34.1
> 
>