[PATCH v2 6/8] evtchn: convert vIRQ lock to an r/w one

[Jan Beulich <jbeulich@xxxxxxxx>]

There's no need to serialize all sending of vIRQ-s; all that's needed
is serialization against the closing of the respective event channels
(so far by means of a barrier). To facilitate the conversion, switch to
an ordinary write locked region in evtchn_close().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Don't introduce/use rw_barrier() here. Add comment to
    evtchn_bind_virq(). Re-base.

--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -160,7 +160,7 @@ struct vcpu *vcpu_create(struct domain *
     v->vcpu_id = vcpu_id;
     v->dirty_cpu = VCPU_CPU_CLEAN;
 
-    spin_lock_init(&v->virq_lock);
+    rwlock_init(&v->virq_lock);
 
     tasklet_init(&v->continue_hypercall_tasklet, NULL, NULL);
 
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -449,6 +449,13 @@ int evtchn_bind_virq(evtchn_bind_virq_t
 
     spin_unlock_irqrestore(&chn->lock, flags);
 
+    /*
+     * If by any, the update of virq_to_evtchn[] would need guarding by
+     * virq_lock, but since this is the last action here, there's no strict
+     * need to acquire the lock. Hnece holding event_lock isn't helpful
+     * anymore at this point, but utilize that its unlocking acts as the
+     * otherwise necessary smp_wmb() here.
+     */
     v->virq_to_evtchn[virq] = bind->port = port;
 
  out:
@@ -638,10 +645,10 @@ int evtchn_close(struct domain *d1, int
     case ECS_VIRQ:
         for_each_vcpu ( d1, v )
         {
-            if ( v->virq_to_evtchn[chn1->u.virq] != port1 )
-                continue;
-            v->virq_to_evtchn[chn1->u.virq] = 0;
-            spin_barrier(&v->virq_lock);
+            write_lock_irqsave(&v->virq_lock, flags);
+            if ( v->virq_to_evtchn[chn1->u.virq] == port1 )
+                v->virq_to_evtchn[chn1->u.virq] = 0;
+            write_unlock_irqrestore(&v->virq_lock, flags);
         }
         break;
 
@@ -797,7 +804,7 @@ void send_guest_vcpu_virq(struct vcpu *v
 
     ASSERT(!virq_is_global(virq));
 
-    spin_lock_irqsave(&v->virq_lock, flags);
+    read_lock_irqsave(&v->virq_lock, flags);
 
     port = v->virq_to_evtchn[virq];
     if ( unlikely(port == 0) )
@@ -807,7 +814,7 @@ void send_guest_vcpu_virq(struct vcpu *v
     evtchn_port_set_pending(d, v->vcpu_id, evtchn_from_port(d, port));
 
  out:
-    spin_unlock_irqrestore(&v->virq_lock, flags);
+    read_unlock_irqrestore(&v->virq_lock, flags);
 }
 
 void send_guest_global_virq(struct domain *d, uint32_t virq)
@@ -826,7 +833,7 @@ void send_guest_global_virq(struct domai
     if ( unlikely(v == NULL) )
         return;
 
-    spin_lock_irqsave(&v->virq_lock, flags);
+    read_lock_irqsave(&v->virq_lock, flags);
 
     port = v->virq_to_evtchn[virq];
     if ( unlikely(port == 0) )
@@ -836,7 +843,7 @@ void send_guest_global_virq(struct domai
     evtchn_port_set_pending(d, chn->notify_vcpu_id, chn);
 
  out:
-    spin_unlock_irqrestore(&v->virq_lock, flags);
+    read_unlock_irqrestore(&v->virq_lock, flags);
 }
 
 void send_guest_pirq(struct domain *d, const struct pirq *pirq)
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -235,7 +235,7 @@ struct vcpu
 
     /* IRQ-safe virq_lock protects against delivering VIRQ to stale evtchn. */
     evtchn_port_t    virq_to_evtchn[NR_VIRQS];
-    spinlock_t       virq_lock;
+    rwlock_t         virq_lock;
 
     /* Tasklet for continue_hypercall_on_cpu(). */
     struct tasklet   continue_hypercall_tasklet;