Subject: [patch 26/30] xen/events: Use immediate affinity setting

From: Thomas Gleixner <[email-masked]>
Date: Thu, 10 Dec 2020 20:26:02 +0100

There is absolutely no reason to mimic the x86 deferred affinity
setting. This mechanism is required to handle the hardware induced issues
of IO/APIC and MSI and is not in use when the interrupts are remapped.

XEN does not need this and can simply change the affinity from the calling
context. The core code invokes this with the interrupt descriptor lock held
so it is fully serialized against any other operation.

Mark the interrupts with IRQ_MOVE_PCNTXT to disable the deferred affinity
setting. The conditional mask/unmask operation is already handled in
xen_rebind_evtchn_to_cpu().

This makes XEN on x86 use the same mechanics as on e.g. ARM64 where
deferred affinity setting is not required and not implemented and the code
path in the ack functions is compiled out.

Signed-off-by: Thomas Gleixner <[email-masked]>
Cc: Boris Ostrovsky <[email-masked]>
Cc: Juergen Gross <[email-masked]>
Cc: Stefano Stabellini <[email-masked]>
Cc: [email-masked]
---
 drivers/xen/events/events_base.c |   35 +++++++++--------------------------
 1 file changed, 9 insertions(+), 26 deletions(-)

--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -628,6 +628,11 @@ static void xen_irq_init(unsigned irq)
 	info->refcnt = -1;
 
 	set_info_for_irq(irq, info);
+	/*
+	 * Interrupt affinity setting can be immediate. No point
+	 * in delaying it until an interrupt is handled.
+	 */
+	irq_set_status_flags(irq, IRQ_MOVE_PCNTXT);
 
 	INIT_LIST_HEAD(&info->eoi_list);
 	list_add_tail(&info->list, &xen_irq_list_head);
@@ -739,18 +744,7 @@ static void eoi_pirq(struct irq_data *da
 	if (!VALID_EVTCHN(evtchn))
 		return;
 
-	if (unlikely(irqd_is_setaffinity_pending(data)) &&
-	    likely(!irqd_irq_disabled(data))) {
-		int masked = test_and_set_mask(evtchn);
-
-		clear_evtchn(evtchn);
-
-		irq_move_masked_irq(data);
-
-		if (!masked)
-			unmask_evtchn(evtchn);
-	} else
-		clear_evtchn(evtchn);
+	clear_evtchn(evtchn);
 
 	if (pirq_needs_eoi(data->irq)) {
 		rc = HYPERVISOR_physdev_op(PHYSDEVOP_eoi, &eoi);
@@ -1641,7 +1635,6 @@ void rebind_evtchn_irq(evtchn_port_t evt
 	mutex_unlock(&irq_mapping_update_lock);
 
         bind_evtchn_to_cpu(evtchn, info->cpu);
-	/* This will be deferred until interrupt is processed */
 	irq_set_affinity(irq, cpumask_of(info->cpu));
 
 	/* Unmask the event channel. */
@@ -1688,8 +1681,9 @@ static int set_affinity_irq(struct irq_d
 			    bool force)
 {
 	unsigned tcpu = cpumask_first_and(dest, cpu_online_mask);
-	int ret = xen_rebind_evtchn_to_cpu(evtchn_from_irq(data->irq), tcpu);
+	int ret;
 
+	ret = xen_rebind_evtchn_to_cpu(evtchn_from_irq(data->irq), tcpu);
 	if (!ret)
 		irq_data_update_effective_affinity(data, cpumask_of(tcpu));
 
@@ -1719,18 +1713,7 @@ static void ack_dynirq(struct irq_data *
 	if (!VALID_EVTCHN(evtchn))
 		return;
 
-	if (unlikely(irqd_is_setaffinity_pending(data)) &&
-	    likely(!irqd_irq_disabled(data))) {
-		int masked = test_and_set_mask(evtchn);
-
-		clear_evtchn(evtchn);
-
-		irq_move_masked_irq(data);
-
-		if (!masked)
-			unmask_evtchn(evtchn);
-	} else
-		clear_evtchn(evtchn);
+	clear_evtchn(evtchn);
 }
 
 static void mask_ack_dynirq(struct irq_data *data)