Re: [Xen-devel] [PATCH v2 20/21] xen: support console_switching between Dom0 and DomUs on ARM

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 17 Jul 2018, Julien Grall wrote:
> Hi Stefano,
> 
> On 07/07/2018 00:12, 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.
> > 
> > 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 v2:
> > - only call vpl011_rx_char if the vpl011 has been initialized
> > ---
> >   xen/drivers/char/console.c | 50
> > ++++++++++++++++++++++++++++++++--------------
> >   1 file changed, 35 insertions(+), 15 deletions(-)
> > 
> > diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> > index 0f05369..d590bc0 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. */
> > @@ -389,29 +392,49 @@ 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.
> > */
> > +static int __read_mostly xen_rx = 1; /* 1 => input passed to domain 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]);
> > +    xen_rx++;
> > +    if ( xen_rx == max_init_domid + 1 )
> > +        xen_rx = 0;
> > +
> > +    if ( !xen_rx )
> > +        printk("*** Serial input xen_rx=%d -> %s", xen_rx, "Xen");
> > +    else
> > +        printk("*** Serial input xen_rx=%d -> DOM%d", xen_rx, xen_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 ( xen_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;
> > +    if ( xen_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_ARM
> > +    else
> > +    {
> > +        struct domain *d = get_domain_by_id(xen_rx - 1);
> > +        if ( !d->arch.vpl011.ring_enable && d->arch.vpl011.inring != NULL )
> 
> It sounds like you want to provide a macro here. So would make clearer what
> you are actually checking.

I would rather add a in-code comment because it is the only instance of
this check in the codebase.


> > +            vpl011_rx_char(d, c);
> 
> What happen in the case vpl011 is not enabled for that domain?

Yes, that is a mistake in this version of the series. I have already
fixed the issue in my v3 dev branch.


> Shouldn't you at least warn there are no console available?

I'll add a warning


> > +    }
> > +#endif
> >       /* Always notify the guest: prevents receive path from getting stuck.
> > */
> 
> This comment seems a bit wrong now, altough the comment seem to suggest may
> need to be taken care.

I'll update the comment, it is only relevant to the hardware domain


> >       send_global_virq(VIRQ_CONSOLE);
> >   @@ -923,7 +946,7 @@ void __init console_endboot(void)
> >        * a useful 'how to switch' message.
> >        */
> >       if ( opt_conswitch[1] == 'x' )
> > -        xen_rx = !xen_rx;
> > +        xen_rx = 0;
> >         register_keyhandler('w', dump_console_ring_key,
> >                           "synchronously dump console ring buffer (dmesg)",
> > 0);
> > @@ -933,9 +956,6 @@ void __init console_endboot(void)
> >                               "decrease log level threshold", 0);
> >       register_irq_keyhandler('G', &do_toggle_guest,
> >                               "toggle host/guest log level adjustment", 0);
> > -
> > -    /* Serial input is directed to DOM0 by default. */
> > -    switch_serial_input();
> >   }
> >     int __init console_has(const char *device)

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