[PATCH v2 0/5] xen: event handling cleanup

[PATCH v2 0/5] xen: event handling cleanup

[Juergen Gross]

Do some cleanups in Xen event handling code.

Changes in V2:
- addressed comments

Juergen Gross (5):
  xen: remove no longer used functions
  xen/events: make struct irq_info private to events_base.c
  xen/events: only register debug interrupt for 2-level events
  xen/events: unmask a fifo event channel only if it was masked
  Documentation: add xen.fifo_events kernel parameter description

 .../admin-guide/kernel-parameters.txt         |  7 ++
 arch/x86/xen/smp.c                            | 19 ++--
 arch/x86/xen/xen-ops.h                        |  2 +
 drivers/xen/events/events_2l.c                |  7 +-
 drivers/xen/events/events_base.c              | 94 +++++++++++++------
 drivers/xen/events/events_fifo.c              |  9 +-
 drivers/xen/events/events_internal.h          | 70 ++------------
 include/xen/events.h                          |  8 --
 8 files changed, 102 insertions(+), 114 deletions(-)

-- 
2.26.2

[PATCH v2 1/5] xen: remove no longer used functions

[Juergen Gross]

With the switch to the lateeoi model for interdomain event channels
some functions are no longer in use. Remove them.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
 drivers/xen/events/events_base.c | 21 ---------------------
 include/xen/events.h             |  8 --------
 2 files changed, 29 deletions(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index cc317739e786..436682db41c5 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -1145,14 +1145,6 @@ static int bind_interdomain_evtchn_to_irq_chip(unsigned int remote_domain,
 					       chip);
 }
 
-int bind_interdomain_evtchn_to_irq(unsigned int remote_domain,
-				   evtchn_port_t remote_port)
-{
-	return bind_interdomain_evtchn_to_irq_chip(remote_domain, remote_port,
-						   &xen_dynamic_chip);
-}
-EXPORT_SYMBOL_GPL(bind_interdomain_evtchn_to_irq);
-
 int bind_interdomain_evtchn_to_irq_lateeoi(unsigned int remote_domain,
 					   evtchn_port_t remote_port)
 {
@@ -1320,19 +1312,6 @@ static int bind_interdomain_evtchn_to_irqhandler_chip(
 	return irq;
 }
 
-int bind_interdomain_evtchn_to_irqhandler(unsigned int remote_domain,
-					  evtchn_port_t remote_port,
-					  irq_handler_t handler,
-					  unsigned long irqflags,
-					  const char *devname,
-					  void *dev_id)
-{
-	return bind_interdomain_evtchn_to_irqhandler_chip(remote_domain,
-				remote_port, handler, irqflags, devname,
-				dev_id, &xen_dynamic_chip);
-}
-EXPORT_SYMBOL_GPL(bind_interdomain_evtchn_to_irqhandler);
-
 int bind_interdomain_evtchn_to_irqhandler_lateeoi(unsigned int remote_domain,
 						  evtchn_port_t remote_port,
 						  irq_handler_t handler,
diff --git a/include/xen/events.h b/include/xen/events.h
index 3b8155c2ea03..8ec418e30c7f 100644
--- a/include/xen/events.h
+++ b/include/xen/events.h
@@ -35,16 +35,8 @@ int bind_ipi_to_irqhandler(enum ipi_vector ipi,
 			   unsigned long irqflags,
 			   const char *devname,
 			   void *dev_id);
-int bind_interdomain_evtchn_to_irq(unsigned int remote_domain,
-				   evtchn_port_t remote_port);
 int bind_interdomain_evtchn_to_irq_lateeoi(unsigned int remote_domain,
 					   evtchn_port_t remote_port);
-int bind_interdomain_evtchn_to_irqhandler(unsigned int remote_domain,
-					  evtchn_port_t remote_port,
-					  irq_handler_t handler,
-					  unsigned long irqflags,
-					  const char *devname,
-					  void *dev_id);
 int bind_interdomain_evtchn_to_irqhandler_lateeoi(unsigned int remote_domain,
 						  evtchn_port_t remote_port,
 						  irq_handler_t handler,
-- 
2.26.2

[PATCH v2 2/5] xen/events: make struct irq_info private to events_base.c

[Juergen Gross]

The struct irq_info of Xen's event handling is used only for two
evtchn_ops functions outside of events_base.c. Those two functions
can easily be switched to avoid that usage.

This allows to make struct irq_info and its related access functions
private to events_base.c.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
 drivers/xen/events/events_2l.c       |  7 +--
 drivers/xen/events/events_base.c     | 63 ++++++++++++++++++++++---
 drivers/xen/events/events_fifo.c     |  6 +--
 drivers/xen/events/events_internal.h | 70 ++++------------------------
 4 files changed, 73 insertions(+), 73 deletions(-)

diff --git a/drivers/xen/events/events_2l.c b/drivers/xen/events/events_2l.c
index fe5ad0e89cd8..da87f3a1e351 100644
--- a/drivers/xen/events/events_2l.c
+++ b/drivers/xen/events/events_2l.c
@@ -47,10 +47,11 @@ static unsigned evtchn_2l_max_channels(void)
 	return EVTCHN_2L_NR_CHANNELS;
 }
 
-static void evtchn_2l_bind_to_cpu(struct irq_info *info, unsigned cpu)
+static void evtchn_2l_bind_to_cpu(evtchn_port_t evtchn, unsigned int cpu,
+				  unsigned int old_cpu)
 {
-	clear_bit(info->evtchn, BM(per_cpu(cpu_evtchn_mask, info->cpu)));
-	set_bit(info->evtchn, BM(per_cpu(cpu_evtchn_mask, cpu)));
+	clear_bit(evtchn, BM(per_cpu(cpu_evtchn_mask, old_cpu)));
+	set_bit(evtchn, BM(per_cpu(cpu_evtchn_mask, cpu)));
 }
 
 static void evtchn_2l_clear_pending(evtchn_port_t port)
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 436682db41c5..1c25580c7691 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -70,6 +70,57 @@
 #undef MODULE_PARAM_PREFIX
 #define MODULE_PARAM_PREFIX "xen."
 
+/* Interrupt types. */
+enum xen_irq_type {
+	IRQT_UNBOUND = 0,
+	IRQT_PIRQ,
+	IRQT_VIRQ,
+	IRQT_IPI,
+	IRQT_EVTCHN
+};
+
+/*
+ * Packed IRQ information:
+ * type - enum xen_irq_type
+ * event channel - irq->event channel mapping
+ * cpu - cpu this event channel is bound to
+ * index - type-specific information:
+ *    PIRQ - vector, with MSB being "needs EIO", or physical IRQ of the HVM
+ *           guest, or GSI (real passthrough IRQ) of the device.
+ *    VIRQ - virq number
+ *    IPI - IPI vector
+ *    EVTCHN -
+ */
+struct irq_info {
+	struct list_head list;
+	struct list_head eoi_list;
+	short refcnt;
+	short spurious_cnt;
+	enum xen_irq_type type; /* type */
+	unsigned irq;
+	evtchn_port_t evtchn;   /* event channel */
+	unsigned short cpu;     /* cpu bound */
+	unsigned short eoi_cpu; /* EOI must happen on this cpu-1 */
+	unsigned int irq_epoch; /* If eoi_cpu valid: irq_epoch of event */
+	u64 eoi_time;           /* Time in jiffies when to EOI. */
+
+	union {
+		unsigned short virq;
+		enum ipi_vector ipi;
+		struct {
+			unsigned short pirq;
+			unsigned short gsi;
+			unsigned char vector;
+			unsigned char flags;
+			uint16_t domid;
+		} pirq;
+	} u;
+};
+
+#define PIRQ_NEEDS_EOI	(1 << 0)
+#define PIRQ_SHAREABLE	(1 << 1)
+#define PIRQ_MSI_GROUP	(1 << 2)
+
 static uint __read_mostly event_loop_timeout = 2;
 module_param(event_loop_timeout, uint, 0644);
 
@@ -110,7 +161,7 @@ static DEFINE_PER_CPU(int [NR_VIRQS], virq_to_irq) = {[0 ... NR_VIRQS-1] = -1};
 /* IRQ <-> IPI mapping */
 static DEFINE_PER_CPU(int [XEN_NR_IPIS], ipi_to_irq) = {[0 ... XEN_NR_IPIS-1] = -1};
 
-int **evtchn_to_irq;
+static int **evtchn_to_irq;
 #ifdef CONFIG_X86
 static unsigned long *pirq_eoi_map;
 #endif
@@ -190,7 +241,7 @@ int get_evtchn_to_irq(evtchn_port_t evtchn)
 }
 
 /* Get info for IRQ */
-struct irq_info *info_for_irq(unsigned irq)
+static struct irq_info *info_for_irq(unsigned irq)
 {
 	if (irq < nr_legacy_irqs())
 		return legacy_info_ptrs[irq];
@@ -228,7 +279,7 @@ static int xen_irq_info_common_setup(struct irq_info *info,
 
 	irq_clear_status_flags(irq, IRQ_NOREQUEST|IRQ_NOAUTOEN);
 
-	return xen_evtchn_port_setup(info);
+	return xen_evtchn_port_setup(evtchn);
 }
 
 static int xen_irq_info_evtchn_setup(unsigned irq,
@@ -351,7 +402,7 @@ static enum xen_irq_type type_from_irq(unsigned irq)
 	return info_for_irq(irq)->type;
 }
 
-unsigned cpu_from_irq(unsigned irq)
+static unsigned cpu_from_irq(unsigned irq)
 {
 	return info_for_irq(irq)->cpu;
 }
@@ -391,7 +442,7 @@ static void bind_evtchn_to_cpu(evtchn_port_t evtchn, unsigned int cpu)
 #ifdef CONFIG_SMP
 	cpumask_copy(irq_get_affinity_mask(irq), cpumask_of(cpu));
 #endif
-	xen_evtchn_port_bind_to_cpu(info, cpu);
+	xen_evtchn_port_bind_to_cpu(evtchn, cpu, info->cpu);
 
 	info->cpu = cpu;
 }
@@ -745,7 +796,7 @@ static unsigned int __startup_pirq(unsigned int irq)
 	info->evtchn = evtchn;
 	bind_evtchn_to_cpu(evtchn, 0);
 
-	rc = xen_evtchn_port_setup(info);
+	rc = xen_evtchn_port_setup(evtchn);
 	if (rc)
 		goto err;
 
diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 6085a808da95..243e7b6d7b96 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -138,9 +138,8 @@ static void init_array_page(event_word_t *array_page)
 		array_page[i] = 1 << EVTCHN_FIFO_MASKED;
 }
 
-static int evtchn_fifo_setup(struct irq_info *info)
+static int evtchn_fifo_setup(evtchn_port_t port)
 {
-	evtchn_port_t port = info->evtchn;
 	unsigned new_array_pages;
 	int ret;
 
@@ -186,7 +185,8 @@ static int evtchn_fifo_setup(struct irq_info *info)
 	return ret;
 }
 
-static void evtchn_fifo_bind_to_cpu(struct irq_info *info, unsigned cpu)
+static void evtchn_fifo_bind_to_cpu(evtchn_port_t evtchn, unsigned int cpu, 
+				    unsigned int old_cpu)
 {
 	/* no-op */
 }
diff --git a/drivers/xen/events/events_internal.h b/drivers/xen/events/events_internal.h
index 82937d90d7d7..0a97c0549db7 100644
--- a/drivers/xen/events/events_internal.h
+++ b/drivers/xen/events/events_internal.h
@@ -7,65 +7,15 @@
 #ifndef __EVENTS_INTERNAL_H__
 #define __EVENTS_INTERNAL_H__
 
-/* Interrupt types. */
-enum xen_irq_type {
-	IRQT_UNBOUND = 0,
-	IRQT_PIRQ,
-	IRQT_VIRQ,
-	IRQT_IPI,
-	IRQT_EVTCHN
-};
-
-/*
- * Packed IRQ information:
- * type - enum xen_irq_type
- * event channel - irq->event channel mapping
- * cpu - cpu this event channel is bound to
- * index - type-specific information:
- *    PIRQ - vector, with MSB being "needs EIO", or physical IRQ of the HVM
- *           guest, or GSI (real passthrough IRQ) of the device.
- *    VIRQ - virq number
- *    IPI - IPI vector
- *    EVTCHN -
- */
-struct irq_info {
-	struct list_head list;
-	struct list_head eoi_list;
-	short refcnt;
-	short spurious_cnt;
-	enum xen_irq_type type;	/* type */
-	unsigned irq;
-	evtchn_port_t evtchn;	/* event channel */
-	unsigned short cpu;	/* cpu bound */
-	unsigned short eoi_cpu;	/* EOI must happen on this cpu */
-	unsigned int irq_epoch;	/* If eoi_cpu valid: irq_epoch of event */
-	u64 eoi_time;		/* Time in jiffies when to EOI. */
-
-	union {
-		unsigned short virq;
-		enum ipi_vector ipi;
-		struct {
-			unsigned short pirq;
-			unsigned short gsi;
-			unsigned char vector;
-			unsigned char flags;
-			uint16_t domid;
-		} pirq;
-	} u;
-};
-
-#define PIRQ_NEEDS_EOI	(1 << 0)
-#define PIRQ_SHAREABLE	(1 << 1)
-#define PIRQ_MSI_GROUP	(1 << 2)
-
 struct evtchn_loop_ctrl;
 
 struct evtchn_ops {
 	unsigned (*max_channels)(void);
 	unsigned (*nr_channels)(void);
 
-	int (*setup)(struct irq_info *info);
-	void (*bind_to_cpu)(struct irq_info *info, unsigned cpu);
+	int (*setup)(evtchn_port_t port);
+	void (*bind_to_cpu)(evtchn_port_t evtchn, unsigned int cpu,
+			    unsigned int old_cpu);
 
 	void (*clear_pending)(evtchn_port_t port);
 	void (*set_pending)(evtchn_port_t port);
@@ -83,12 +33,9 @@ struct evtchn_ops {
 
 extern const struct evtchn_ops *evtchn_ops;
 
-extern int **evtchn_to_irq;
 int get_evtchn_to_irq(evtchn_port_t evtchn);
 void handle_irq_for_port(evtchn_port_t port, struct evtchn_loop_ctrl *ctrl);
 
-struct irq_info *info_for_irq(unsigned irq);
-unsigned cpu_from_irq(unsigned irq);
 unsigned int cpu_from_evtchn(evtchn_port_t evtchn);
 
 static inline unsigned xen_evtchn_max_channels(void)
@@ -100,17 +47,18 @@ static inline unsigned xen_evtchn_max_channels(void)
  * Do any ABI specific setup for a bound event channel before it can
  * be unmasked and used.
  */
-static inline int xen_evtchn_port_setup(struct irq_info *info)
+static inline int xen_evtchn_port_setup(evtchn_port_t evtchn)
 {
 	if (evtchn_ops->setup)
-		return evtchn_ops->setup(info);
+		return evtchn_ops->setup(evtchn);
 	return 0;
 }
 
-static inline void xen_evtchn_port_bind_to_cpu(struct irq_info *info,
-					       unsigned cpu)
+static inline void xen_evtchn_port_bind_to_cpu(evtchn_port_t evtchn,
+					       unsigned int cpu,
+					       unsigned int old_cpu)
 {
-	evtchn_ops->bind_to_cpu(info, cpu);
+	evtchn_ops->bind_to_cpu(evtchn, cpu, old_cpu);
 }
 
 static inline void clear_evtchn(evtchn_port_t port)
-- 
2.26.2

[PATCH v2 3/5] xen/events: only register debug interrupt for 2-level events

[Juergen Gross]

xen_debug_interrupt() is specific to 2-level event handling. So don't
register it with fifo event handling being active.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
V2:
- rename fifo_events variable to xen_fifo_events (Jan Beulich)
---
 arch/x86/xen/smp.c               | 19 +++++++++++--------
 arch/x86/xen/xen-ops.h           |  2 ++
 drivers/xen/events/events_base.c | 10 ++++++----
 3 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 2097fa0ebdb5..c1b2f764b29a 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -88,14 +88,17 @@ int xen_smp_intr_init(unsigned int cpu)
 	per_cpu(xen_callfunc_irq, cpu).irq = rc;
 	per_cpu(xen_callfunc_irq, cpu).name = callfunc_name;
 
-	debug_name = kasprintf(GFP_KERNEL, "debug%d", cpu);
-	rc = bind_virq_to_irqhandler(VIRQ_DEBUG, cpu, xen_debug_interrupt,
-				     IRQF_PERCPU | IRQF_NOBALANCING,
-				     debug_name, NULL);
-	if (rc < 0)
-		goto fail;
-	per_cpu(xen_debug_irq, cpu).irq = rc;
-	per_cpu(xen_debug_irq, cpu).name = debug_name;
+	if (!xen_fifo_events) {
+		debug_name = kasprintf(GFP_KERNEL, "debug%d", cpu);
+		rc = bind_virq_to_irqhandler(VIRQ_DEBUG, cpu,
+					     xen_debug_interrupt,
+					     IRQF_PERCPU | IRQF_NOBALANCING,
+					     debug_name, NULL);
+		if (rc < 0)
+			goto fail;
+		per_cpu(xen_debug_irq, cpu).irq = rc;
+		per_cpu(xen_debug_irq, cpu).name = debug_name;
+	}
 
 	callfunc_name = kasprintf(GFP_KERNEL, "callfuncsingle%d", cpu);
 	rc = bind_ipi_to_irqhandler(XEN_CALL_FUNCTION_SINGLE_VECTOR,
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 45d556f71858..9546c3384c75 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -29,6 +29,8 @@ extern struct start_info *xen_start_info;
 extern struct shared_info xen_dummy_shared_info;
 extern struct shared_info *HYPERVISOR_shared_info;
 
+extern bool xen_fifo_events;
+
 void xen_setup_mfn_list_list(void);
 void xen_build_mfn_list_list(void);
 void xen_setup_machphys_mapping(void);
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 1c25580c7691..6038c4c35db5 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -2050,8 +2050,8 @@ void xen_setup_callback_vector(void) {}
 static inline void xen_alloc_callback_vector(void) {}
 #endif
 
-static bool fifo_events = true;
-module_param(fifo_events, bool, 0);
+bool xen_fifo_events = true;
+module_param_named(fifo_events, xen_fifo_events, bool, 0);
 
 static int xen_evtchn_cpu_prepare(unsigned int cpu)
 {
@@ -2080,10 +2080,12 @@ void __init xen_init_IRQ(void)
 	int ret = -EINVAL;
 	evtchn_port_t evtchn;
 
-	if (fifo_events)
+	if (xen_fifo_events)
 		ret = xen_evtchn_fifo_init();
-	if (ret < 0)
+	if (ret < 0) {
 		xen_evtchn_2l_init();
+		xen_fifo_events = false;
+	}
 
 	xen_cpu_init_eoi(smp_processor_id());
 
-- 
2.26.2

Re: [PATCH v2 3/5] xen/events: only register debug interrupt for 2-level events

[Jan Beulich]

On 22.10.2020 11:49, Juergen Gross wrote:
> @@ -2080,10 +2080,12 @@ void __init xen_init_IRQ(void)
>  	int ret = -EINVAL;
>  	evtchn_port_t evtchn;
>  
> -	if (fifo_events)
> +	if (xen_fifo_events)
>  		ret = xen_evtchn_fifo_init();
> -	if (ret < 0)
> +	if (ret < 0) {
>  		xen_evtchn_2l_init();
> +		xen_fifo_events = false;
> +	}

Another note: While it may not matter right here, maybe better
first set the variable and the call the function?

Jan

Re: [PATCH v2 3/5] xen/events: only register debug interrupt for 2-level events

[Jürgen Groß]

On 22.10.20 12:35, Jan Beulich wrote:
> On 22.10.2020 11:49, Juergen Gross wrote:
>> @@ -2080,10 +2080,12 @@ void __init xen_init_IRQ(void)
>>   	int ret = -EINVAL;
>>   	evtchn_port_t evtchn;
>>   
>> -	if (fifo_events)
>> +	if (xen_fifo_events)
>>   		ret = xen_evtchn_fifo_init();
>> -	if (ret < 0)
>> +	if (ret < 0) {
>>   		xen_evtchn_2l_init();
>> +		xen_fifo_events = false;
>> +	}
> 
> Another note: While it may not matter right here, maybe better
> first set the variable and the call the function?

I don't think this is really important, TBH.

This code is executed before other cpus are up and we'd have major
other problems in case the sequence would really matter here.


Juergen

Re: [PATCH v2 3/5] xen/events: only register debug interrupt for 2-level events

[Jan Beulich]

On 22.10.2020 15:09, Jürgen Groß wrote:
> On 22.10.20 12:35, Jan Beulich wrote:
>> On 22.10.2020 11:49, Juergen Gross wrote:
>>> @@ -2080,10 +2080,12 @@ void __init xen_init_IRQ(void)
>>>   	int ret = -EINVAL;
>>>   	evtchn_port_t evtchn;
>>>   
>>> -	if (fifo_events)
>>> +	if (xen_fifo_events)
>>>   		ret = xen_evtchn_fifo_init();
>>> -	if (ret < 0)
>>> +	if (ret < 0) {
>>>   		xen_evtchn_2l_init();
>>> +		xen_fifo_events = false;
>>> +	}
>>
>> Another note: While it may not matter right here, maybe better
>> first set the variable and the call the function?
> 
> I don't think this is really important, TBH.
> 
> This code is executed before other cpus are up and we'd have major
> other problems in case the sequence would really matter here.

Fair enough; I was thinking in particular that it ought to be
legitimate for xen_evtchn_2l_init() to BUG_ON(xen_fifo_events).

Jan

[PATCH v2 4/5] xen/events: unmask a fifo event channel only if it was masked

[Juergen Gross]

Unmasking an event channel with fifo events channels being used can
require a hypercall to be made, so try to avoid that by checking
whether the event channel was really masked.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
V2:
- move test for already unmasked into loop (Jan Beulich)
---
 drivers/xen/events/events_fifo.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 243e7b6d7b96..b234f1766810 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -237,6 +237,9 @@ static bool clear_masked_cond(volatile event_word_t *word)
 	w = *word;
 
 	do {
+		if (!(w & (1 << EVTCHN_FIFO_MASKED)))
+			return true;
+
 		if (w & (1 << EVTCHN_FIFO_PENDING))
 			return false;
 
-- 
2.26.2

[PATCH v2 5/5] Documentation: add xen.fifo_events kernel parameter description

[Juergen Gross]

The kernel boot parameter xen.fifo_events isn't listed in
Documentation/admin-guide/kernel-parameters.txt. Add it.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 02d4adbf98d2..526d65d8573a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5978,6 +5978,13 @@
 			After which time (jiffies) the event handling loop
 			should start to delay EOI handling. Default is 2.
 
+	xen.fifo_events=	[XEN]
+			Boolean parameter to disable using fifo event handling
+			even if available. Normally fifo event handling is
+			preferred over the 2-level event handling, as it is
+			fairer and the number of possible event channels is
+			much higher. Default is on (use fifo events).
+
 	nopv=		[X86,XEN,KVM,HYPER_V,VMWARE]
 			Disables the PV optimizations forcing the guest to run
 			as generic guest with no PV drivers. Currently support
-- 
2.26.2

Re: [PATCH v2 0/5] xen: event handling cleanup

[boris.ostrovsky]

On 10/22/20 5:49 AM, Juergen Gross wrote:
> Do some cleanups in Xen event handling code.
>
> Changes in V2:
> - addressed comments
>
> Juergen Gross (5):
>   xen: remove no longer used functions
>   xen/events: make struct irq_info private to events_base.c
>   xen/events: only register debug interrupt for 2-level events
>   xen/events: unmask a fifo event channel only if it was masked
>   Documentation: add xen.fifo_events kernel parameter description
>
>  .../admin-guide/kernel-parameters.txt         |  7 ++
>  arch/x86/xen/smp.c                            | 19 ++--
>  arch/x86/xen/xen-ops.h                        |  2 +
>  drivers/xen/events/events_2l.c                |  7 +-
>  drivers/xen/events/events_base.c              | 94 +++++++++++++------
>  drivers/xen/events/events_fifo.c              |  9 +-
>  drivers/xen/events/events_internal.h          | 70 ++------------
>  include/xen/events.h                          |  8 --
>  8 files changed, 102 insertions(+), 114 deletions(-)
>

Applied to for-linus-5.10b.


-boris