Re: [Xen-devel] [PATCH v3 23/25] xen: support console_switching between Dom0 and DomUs on ARM

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

OOI, on the previous version you said you will explore the CTRL-x N 
solution (where N is the domID console to switch too). What was the 
result here?
On 01/08/18 00:28, Stefano Stabellini wrote:
> Today Ctrl-AAA is used to switch between Xen and Dom0. Extend the
> mechanism to allow for switching between Xen, Dom0, and any of the
> initial DomU created from Xen alongside Dom0 out of information provided
> via device tree.
>
> Rename xen_rx to console_rx to match the new behavior.
>
> Clarify existing comment about "notify the guest", making it clear that
> it is only about the hardware domain.
>
> Export a function named console_input_domain() to allow others to know
> which domains has input at a given time.
>
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> CC: andrew.cooper3@xxxxxxxxxx
> CC: George.Dunlap@xxxxxxxxxxxxx
> CC: ian.jackson@xxxxxxxxxxxxx
> CC: jbeulich@xxxxxxxx
> CC: konrad.wilk@xxxxxxxxxx
> CC: tim@xxxxxxx
> CC: wei.liu2@xxxxxxxxxx
> ---
> Changes in v3:
> - only call vpl011 functions ifdef CONFIG_SBSA_VUART_CONSOLE
> - add blank line and spaces
> - remove xen_rx from print messages
> - rename xen_rx to console_rx
> - keep switch_serial_input() at boot
> - add better comments
> - fix existing comment
> - add warning if no guests console/uart is available
> - add console_input_domain function
>
> Changes in v2:
> - only call vpl011_rx_char if the vpl011 has been initialized
> ---
>   xen/drivers/char/console.c | 71 +++++++++++++++++++++++++++++++++++++---------
>   xen/include/xen/console.h  |  2 ++
>   2 files changed, 60 insertions(+), 13 deletions(-)
>
> diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> index 0f05369..cd4dfb1 100644
> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -31,10 +31,13 @@
>   #include <xen/early_printk.h>
>   #include <xen/warning.h>
>   #include <xen/pv_console.h>
> +#include <asm/setup.h>
>   
>   #ifdef CONFIG_X86
>   #include <xen/consoled.h>
>   #include <asm/guest.h>
> +#else
> +#include <asm/vpl011.h>
>   #endif
>   
>   /* console: comma-separated list of console outputs. */
> @@ -389,30 +392,72 @@ static void dump_console_ring_key(unsigned char key)
>       free_xenheap_pages(buf, order);
>   }
>   
> -/* CTRL-<switch_char> switches input direction between Xen and DOM0. */
> +/*
> + * CTRL-<switch_char> switches input direction between Xen, Dom0 and
> + * DomUs.
> + */
>   #define switch_code (opt_conswitch[0]-'a'+1)
> -static int __read_mostly xen_rx = 1; /* FALSE => input passed to domain 0. */
> +/*
> + * console_rx=0 => input to xen
> + * console_rx=1 => input to dom0
> + * console_rx=N => input dom(N-1)
> + */
> +static int __read_mostly console_rx = 0;
> +
> +struct domain *console_input_domain(void)
> +{
> +    return get_domain_by_id(console_rx - 1);
Please take care of the case where console_rx == 0.

> +}
>   
>   static void switch_serial_input(void)
>   {
> -    static char *input_str[2] = { "DOM0", "Xen" };
> -    xen_rx = !xen_rx;
> -    printk("*** Serial input -> %s", input_str[xen_rx]);
> +    console_rx++;
> +    if ( console_rx == max_init_domid + 2 )
> +        console_rx = 0;
> +
> +    if ( !console_rx )
> +        printk("*** Serial input to Xen");
> +    else
> +        printk("*** Serial input to DOM%d", console_rx - 1);
> +
>       if ( switch_code )
> -        printk(" (type 'CTRL-%c' three times to switch input to %s)",
> -               opt_conswitch[0], input_str[!xen_rx]);
> +        printk(" (type 'CTRL-%c' three times to switch input)",
> +               opt_conswitch[0]);
>       printk("\n");
>   }
>   
>   static void __serial_rx(char c, struct cpu_user_regs *regs)
>   {
> -    if ( xen_rx )
> +    if ( console_rx == 0 )
>           return handle_keypress(c, regs);
>   
> -    /* Deliver input to guest buffer, unless it is already full. */
> -    if ( (serial_rx_prod-serial_rx_cons) != SERIAL_RX_SIZE )
> -        serial_rx_ring[SERIAL_RX_MASK(serial_rx_prod++)] = c;
> -    /* Always notify the guest: prevents receive path from getting stuck. */
> +    if ( console_rx == 1 )
> +    {
> +        /* Deliver input to guest buffer, unless it is already full. */
> +        if ( (serial_rx_prod - serial_rx_cons) != SERIAL_RX_SIZE )
> +            serial_rx_ring[SERIAL_RX_MASK(serial_rx_prod++)] = c;
> +    }
> +#ifdef CONFIG_SBSA_VUART_CONSOLE
> +    else
> +    {
> +        struct domain *d = get_domain_by_id(console_rx - 1);
I don't think this is correct to assume the domain will always be 
present. With this series, it would be possible to retire a domain and 
therefore get_domain_by_id() would return NULL here. This would result 
to a data abort below.
Also, I think you want to use rcu_lock_by_domain here (I am not 100% 
sure though).
> +
> +        /*
> +         * If we have a properly initialized vpl011 console for the
> +         * domain, without a full PV ring to Dom0 (in that case input
> +         * comes from the PV ring), then send the character to it.
> +         */
> +        if ( !d->arch.vpl011.backend_in_domain && d->arch.vpl011.xen != NULL )
> +            vpl011_rx_char_xen(d, c);
> +        else
> +            printk("Cannot send chars to Dom%d: no UART available\n",
> +                   d->domain_id);
> +    }
> +#endif
> +    /*
> +     * Always notify the hardware domain: prevents receive path from
That's not true. If you look at send_global_virq, it will send to the 
domain that register the VIRQ. That may be the hardware domain but could 
be someone else.
However, I still don't understand how this work in presence of multiple 
backend here. Why would you notify Domain B everytime a character is 
redirected to domain A/C/D the console?
> +     * getting stuck.
> +     */
>       send_global_virq(VIRQ_CONSOLE);
>   
>   #ifdef CONFIG_X86
> @@ -923,7 +968,7 @@ void __init console_endboot(void)
>        * a useful 'how to switch' message.
>        */
>       if ( opt_conswitch[1] == 'x' )
> -        xen_rx = !xen_rx;
> +        console_rx = 0;
>   
>       register_keyhandler('w', dump_console_ring_key,
>                           "synchronously dump console ring buffer (dmesg)", 0);
> diff --git a/xen/include/xen/console.h b/xen/include/xen/console.h
> index ea06fd8..2fe3912 100644
> --- a/xen/include/xen/console.h
> +++ b/xen/include/xen/console.h
> @@ -31,6 +31,8 @@ void console_end_sync(void);
>   void console_start_log_everything(void);
>   void console_end_log_everything(void);
>   
> +struct domain *console_input_domain(void);
> +
>   /*
>    * Steal output from the console. Returns +ve identifier, else -ve error.
>    * Takes the handle of the serial line to steal, and steal callback function.
Cheers,

--
Julien Grall

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