Re: [PATCH 1/2] hvc_xen: support PV on HVM consoles

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Jan 26, 2012 at 12:43:26PM +0000, Stefano Stabellini wrote:
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> ---
>  drivers/tty/hvc/hvc_xen.c          |   86 +++++++++++++++++++++++++++++-------
>  include/xen/interface/hvm/params.h |    6 ++-
>  2 files changed, 75 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
> index 52fdf60..dd6641f 100644
> --- a/drivers/tty/hvc/hvc_xen.c
> +++ b/drivers/tty/hvc/hvc_xen.c
> @@ -24,9 +24,12 @@
>  #include <linux/init.h>
>  #include <linux/types.h>
>  
> +#include <asm/io.h>
>  #include <asm/xen/hypervisor.h>
>  
>  #include <xen/xen.h>
> +#include <xen/interface/xen.h>
> +#include <xen/hvm.h>
>  #include <xen/page.h>
>  #include <xen/events.h>
>  #include <xen/interface/io/console.h>
> @@ -42,9 +45,13 @@ static int xencons_irq;
>  /* ------------------------------------------------------------------ */
>  
>  static unsigned long console_pfn = ~0ul;
> +static unsigned int console_evtchn = ~0ul;
> +static struct xencons_interface *xencons_if = NULL;
>  
>  static inline struct xencons_interface *xencons_interface(void)
>  {
> +	if (xencons_if != NULL)
> +		return xencons_if;
>  	if (console_pfn == ~0ul)
>  		return mfn_to_virt(xen_start_info->console.domU.mfn);
>  	else
> @@ -54,7 +61,10 @@ static inline struct xencons_interface *xencons_interface(void)
>  static inline void notify_daemon(void)
>  {
>  	/* Use evtchn: this is called early, before irq is set up. */
> -	notify_remote_via_evtchn(xen_start_info->console.domU.evtchn);
> +	if (console_evtchn == ~0ul)
> +		notify_remote_via_evtchn(xen_start_info->console.domU.evtchn);
> +	else
> +		notify_remote_via_evtchn(console_evtchn);
>  }
>  
>  static int __write_console(const char *data, int len)
> @@ -157,28 +167,65 @@ static struct hv_ops dom0_hvc_ops = {
>  	.notifier_hangup = notifier_hangup_irq,
>  };
>  
> +static int xen_hvm_console_init(void)
> +{
> +	int r;
> +	uint64_t v = 0;
> +	unsigned long mfn;
> +
> +	if (!xen_hvm_domain())
> +		return -ENODEV;
> +
> +	if (xencons_if != NULL)
> +		return -EBUSY;
> +
> +	r = hvm_get_parameter(HVM_PARAM_CONSOLE_EVTCHN, &v);
> +	if (r < 0)
> +		return -ENODEV;
> +	console_evtchn = v;
> +	hvm_get_parameter(HVM_PARAM_CONSOLE_PFN, &v);
> +	if (r < 0)
> +		return -ENODEV;

If we fail here, the console_evtchn is still going to be set
meaning that "notify_daemon"  will use the event channel. Thought
I can't think of the notify daemon being called after the init had
failed so this might not be an issue.

> +	mfn = v;
> +	xencons_if = ioremap(mfn << PAGE_SHIFT, PAGE_SIZE);
> +	if (xencons_if == NULL)
> +		return -ENODEV;

Ditto. If we fail, we have the 'console_evtchn' set to something
else than ~0UL.

> +
> +	return 0;
> +}
> +
>  static int __init xen_hvc_init(void)
>  {
>  	struct hvc_struct *hp;
>  	struct hv_ops *ops;
> +	int r;
>  
> -	if (!xen_pv_domain())
> +	if (!xen_domain())
> +		return -ENODEV;
> +
> +	if (xen_pv_domain() && !xen_initial_domain() &&
> +			!xen_start_info->console.domU.evtchn)

Ewww.. What about just leaving the check:
>  		return -ENODEV;
>  
>  	if (xen_initial_domain()) {
>  		ops = &dom0_hvc_ops;
>  		xencons_irq = bind_virq_to_irq(VIRQ_CONSOLE, 0);
>  	} else {
> -		if (!xen_start_info->console.domU.evtchn)
> -			return -ENODEV;

this one as 'if (xen_pv_domain()) && !xen-..)

That might make the code nicer to read?

> -
>  		ops = &domU_hvc_ops;
> -		xencons_irq = bind_evtchn_to_irq(xen_start_info->console.domU.evtchn);
> +		if (xen_pv_domain()) {
> +			console_pfn = mfn_to_pfn(xen_start_info->console.domU.mfn);
> +			console_evtchn = xen_start_info->console.domU.evtchn;
> +		} else {
> +			r = xen_hvm_console_init();
> +			if (r < 0)
> +				return r;
> +		}
> +		xencons_irq = bind_evtchn_to_irq(console_evtchn);
> +		if (xencons_irq < 0)
> +			xencons_irq = 0; /* NO_IRQ */
> +		else
> +			irq_set_noprobe(xencons_irq);
>  	}
> -	if (xencons_irq < 0)
> -		xencons_irq = 0; /* NO_IRQ */
> -	else
> -		irq_set_noprobe(xencons_irq);
>  
>  	hp = hvc_alloc(HVC_COOKIE, xencons_irq, ops, 256);
>  	if (IS_ERR(hp))
> @@ -186,15 +233,13 @@ static int __init xen_hvc_init(void)
>  
>  	hvc = hp;
>  
> -	console_pfn = mfn_to_pfn(xen_start_info->console.domU.mfn);
> -
>  	return 0;
>  }
>  
>  void xen_console_resume(void)
>  {
>  	if (xencons_irq)
> -		rebind_evtchn_irq(xen_start_info->console.domU.evtchn, xencons_irq);
> +		rebind_evtchn_irq(console_evtchn, xencons_irq);
>  }
>  
>  static void __exit xen_hvc_fini(void)
> @@ -205,16 +250,22 @@ static void __exit xen_hvc_fini(void)
>  
>  static int xen_cons_init(void)
>  {
> -	struct hv_ops *ops;
> +	const struct hv_ops *ops;
>  
> -	if (!xen_pv_domain())
> +	if (!xen_domain())
>  		return 0;
>  
>  	if (xen_initial_domain())
>  		ops = &dom0_hvc_ops;
> -	else
> +	else {
>  		ops = &domU_hvc_ops;
>  
> +		if (xen_pv_domain())
> +			console_evtchn = xen_start_info->console.domU.evtchn;
> +		else
> +			xen_hvm_console_init();
> +	}
> +
>  	hvc_instantiate(HVC_COOKIE, 0, ops);
>  	return 0;
>  }
> @@ -230,6 +281,9 @@ static void xenboot_write_console(struct console *console, const char *string,
>  	unsigned int linelen, off = 0;
>  	const char *pos;
>  
> +	if (!xen_pv_domain())
> +		return;
> +
>  	dom0_write_console(0, string, len);
>  
>  	if (xen_initial_domain())
> diff --git a/include/xen/interface/hvm/params.h b/include/xen/interface/hvm/params.h
> index 1888d8c..1b4f923 100644
> --- a/include/xen/interface/hvm/params.h
> +++ b/include/xen/interface/hvm/params.h
> @@ -90,6 +90,10 @@
>  /* Boolean: Enable aligning all periodic vpts to reduce interrupts */
>  #define HVM_PARAM_VPT_ALIGN    16
>  
> -#define HVM_NR_PARAMS          17
> +/* Console debug shared memory ring and event channel */
> +#define HVM_PARAM_CONSOLE_PFN    17
> +#define HVM_PARAM_CONSOLE_EVTCHN 18
> +
> +#define HVM_NR_PARAMS          19
>  
>  #endif /* __XEN_PUBLIC_HVM_PARAMS_H__ */
> -- 
> 1.7.2.5