[PATCH 11/12] 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
(by means of a barrier). To facilitate the conversion, introduce a new
rw_barrier().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- 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
@@ -640,7 +640,7 @@ int evtchn_close(struct domain *d1, int
             if ( v->virq_to_evtchn[chn1->u.virq] != port1 )
                 continue;
             v->virq_to_evtchn[chn1->u.virq] = 0;
-            spin_barrier(&v->virq_lock);
+            rw_barrier(&v->virq_lock);
         }
         break;
 
@@ -794,7 +794,7 @@ 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 +807,7 @@ void send_guest_vcpu_virq(struct vcpu *v
     spin_unlock(&chn->lock);
 
  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 +826,7 @@ 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) )
@@ -838,7 +838,7 @@ void send_guest_global_virq(struct domai
     spin_unlock(&chn->lock);
 
  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/common/spinlock.c
+++ b/xen/common/spinlock.c
@@ -2,7 +2,7 @@
 #include <xen/irq.h>
 #include <xen/smp.h>
 #include <xen/time.h>
-#include <xen/spinlock.h>
+#include <xen/rwlock.h>
 #include <xen/guest_access.h>
 #include <xen/preempt.h>
 #include <public/sysctl.h>
@@ -334,6 +334,12 @@ void _spin_unlock_recursive(spinlock_t *
     }
 }
 
+void _rw_barrier(rwlock_t *lock)
+{
+    check_barrier(&lock->lock.debug);
+    do { smp_mb(); } while ( _rw_is_locked(lock) );
+}
+
 #ifdef CONFIG_DEBUG_LOCK_PROFILE
 
 struct lock_profile_anc {
--- a/xen/include/xen/rwlock.h
+++ b/xen/include/xen/rwlock.h
@@ -237,6 +237,8 @@ static inline int _rw_is_write_locked(rw
     return (atomic_read(&lock->cnts) & _QW_WMASK) == _QW_LOCKED;
 }
 
+void _rw_barrier(rwlock_t *lock);
+
 #define read_lock(l)                  _read_lock(l)
 #define read_lock_irq(l)              _read_lock_irq(l)
 #define read_lock_irqsave(l, f)                                 \
@@ -266,6 +268,7 @@ static inline int _rw_is_write_locked(rw
 #define rw_is_locked(l)               _rw_is_locked(l)
 #define rw_is_write_locked(l)         _rw_is_write_locked(l)
 
+#define rw_barrier(l)                 _rw_barrier(l)
 
 typedef struct percpu_rwlock percpu_rwlock_t;
 
--- 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;