[Xen-changelog] [xen master] evtchn: use a per-event channel lock for sending events

[patchbot@xxxxxxx]

commit de6acb78bf0e137cbe5b72cee4a35ca018d759cc
Author:     David Vrabel <david.vrabel@xxxxxxxxxx>
AuthorDate: Mon Jun 22 11:39:03 2015 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jun 22 11:39:03 2015 +0200

    evtchn: use a per-event channel lock for sending events
    
    When sending an event, use a new per-event channel lock to safely
    validate the event channel state.
    
    This new lock must be held when changing event channel state.  Note
    that the event channel lock must also be held when changing state from
    ECS_FREE or it will race with a concurrent get_free_port() call.
    
    To avoid having to take the remote event channel locks when sending to
    an interdomain event channel, the local and remote channel locks are
    both held when binding or closing an interdomain event channel.
    
    This significantly  increases the  number of events  that can  be sent
    from multiple  VCPUs.  But struct  evtchn increases in  size, reducing
    the number that fit into a single page to 64 (instead of 128).
    
    Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/common/event_channel.c |   81 +++++++++++++++++++++++++++++++++++++-------
 xen/include/xen/sched.h    |    1 +
 2 files changed, 69 insertions(+), 13 deletions(-)

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index c469db5..09ed5a6 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -139,6 +139,7 @@ static struct evtchn *alloc_evtchn_bucket(struct domain *d, 
unsigned int port)
             return NULL;
         }
         chn[i].port = port + i;
+        spin_lock_init(&chn[i].lock);
     }
     return chn;
 }
@@ -229,11 +230,15 @@ static long evtchn_alloc_unbound(evtchn_alloc_unbound_t 
*alloc)
     if ( rc )
         goto out;
 
+    spin_lock(&chn->lock);
+
     chn->state = ECS_UNBOUND;
     if ( (chn->u.unbound.remote_domid = alloc->remote_dom) == DOMID_SELF )
         chn->u.unbound.remote_domid = current->domain->domain_id;
     evtchn_port_init(d, chn);
 
+    spin_unlock(&chn->lock);
+
     alloc->port = port;
 
  out:
@@ -244,6 +249,28 @@ static long evtchn_alloc_unbound(evtchn_alloc_unbound_t 
*alloc)
 }
 
 
+static void double_evtchn_lock(struct evtchn *lchn, struct evtchn *rchn)
+{
+    if ( lchn < rchn )
+    {
+        spin_lock(&lchn->lock);
+        spin_lock(&rchn->lock);
+    }
+    else
+    {
+        if ( lchn != rchn )
+            spin_lock(&rchn->lock);
+        spin_lock(&lchn->lock);
+    }
+}
+
+static void double_evtchn_unlock(struct evtchn *lchn, struct evtchn *rchn)
+{
+    spin_unlock(&lchn->lock);
+    if ( lchn != rchn )
+        spin_unlock(&rchn->lock);
+}
+
 static long evtchn_bind_interdomain(evtchn_bind_interdomain_t *bind)
 {
     struct evtchn *lchn, *rchn;
@@ -286,6 +313,8 @@ static long 
evtchn_bind_interdomain(evtchn_bind_interdomain_t *bind)
     if ( rc )
         goto out;
 
+    double_evtchn_lock(lchn, rchn);
+
     lchn->u.interdomain.remote_dom  = rd;
     lchn->u.interdomain.remote_port = rport;
     lchn->state                     = ECS_INTERDOMAIN;
@@ -301,6 +330,8 @@ static long 
evtchn_bind_interdomain(evtchn_bind_interdomain_t *bind)
      */
     evtchn_port_set_pending(ld, lchn->notify_vcpu_id, lchn);
 
+    double_evtchn_unlock(lchn, rchn);
+
     bind->local_port = lport;
 
  out:
@@ -341,11 +372,16 @@ static long evtchn_bind_virq(evtchn_bind_virq_t *bind)
         ERROR_EXIT(port);
 
     chn = evtchn_from_port(d, port);
+
+    spin_lock(&chn->lock);
+
     chn->state          = ECS_VIRQ;
     chn->notify_vcpu_id = vcpu;
     chn->u.virq         = virq;
     evtchn_port_init(d, chn);
 
+    spin_unlock(&chn->lock);
+
     v->virq_to_evtchn[virq] = bind->port = port;
 
  out:
@@ -372,10 +408,15 @@ static long evtchn_bind_ipi(evtchn_bind_ipi_t *bind)
         ERROR_EXIT(port);
 
     chn = evtchn_from_port(d, port);
+
+    spin_lock(&chn->lock);
+
     chn->state          = ECS_IPI;
     chn->notify_vcpu_id = vcpu;
     evtchn_port_init(d, chn);
 
+    spin_unlock(&chn->lock);
+
     bind->port = port;
 
  out:
@@ -450,11 +491,15 @@ static long evtchn_bind_pirq(evtchn_bind_pirq_t *bind)
         goto out;
     }
 
+    spin_lock(&chn->lock);
+
     chn->state  = ECS_PIRQ;
     chn->u.pirq.irq = pirq;
     link_pirq_port(port, chn, v);
     evtchn_port_init(d, chn);
 
+    spin_unlock(&chn->lock);
+
     bind->port = port;
 
 #ifdef CONFIG_X86
@@ -575,15 +620,24 @@ static long evtchn_close(struct domain *d1, int port1, 
bool_t guest)
         BUG_ON(chn2->state != ECS_INTERDOMAIN);
         BUG_ON(chn2->u.interdomain.remote_dom != d1);
 
+        double_evtchn_lock(chn1, chn2);
+
+        free_evtchn(d1, chn1);
+
         chn2->state = ECS_UNBOUND;
         chn2->u.unbound.remote_domid = d1->domain_id;
-        break;
+
+        double_evtchn_unlock(chn1, chn2);
+
+        goto out;
 
     default:
         BUG();
     }
 
+    spin_lock(&chn1->lock);
     free_evtchn(d1, chn1);
+    spin_unlock(&chn1->lock);
 
  out:
     if ( d2 != NULL )
@@ -604,21 +658,18 @@ int evtchn_send(struct domain *ld, unsigned int lport)
     struct domain *rd;
     int            rport, ret = 0;
 
-    spin_lock(&ld->event_lock);
-
-    if ( unlikely(!port_is_valid(ld, lport)) )
-    {
-        spin_unlock(&ld->event_lock);
+    if ( !port_is_valid(ld, lport) )
         return -EINVAL;
-    }
 
     lchn = evtchn_from_port(ld, lport);
 
+    spin_lock(&lchn->lock);
+
     /* Guest cannot send via a Xen-attached event channel. */
     if ( unlikely(consumer_is_xen(lchn)) )
     {
-        spin_unlock(&ld->event_lock);
-        return -EINVAL;
+        ret = -EINVAL;
+        goto out;
     }
 
     ret = xsm_evtchn_send(XSM_HOOK, ld, lchn);
@@ -647,7 +698,7 @@ int evtchn_send(struct domain *ld, unsigned int lport)
     }
 
 out:
-    spin_unlock(&ld->event_lock);
+    spin_unlock(&lchn->lock);
 
     return ret;
 }
@@ -1154,11 +1205,15 @@ int alloc_unbound_xen_event_channel(
     if ( rc )
         goto out;
 
+    spin_lock(&chn->lock);
+
     chn->state = ECS_UNBOUND;
     chn->xen_consumer = get_xen_consumer(notification_fn);
     chn->notify_vcpu_id = lvcpu;
     chn->u.unbound.remote_domid = remote_domid;
 
+    spin_unlock(&chn->lock);
+
  out:
     spin_unlock(&ld->event_lock);
 
@@ -1178,11 +1233,11 @@ void notify_via_xen_event_channel(struct domain *ld, 
int lport)
     struct evtchn *lchn, *rchn;
     struct domain *rd;
 
-    spin_lock(&ld->event_lock);
-
     ASSERT(port_is_valid(ld, lport));
     lchn = evtchn_from_port(ld, lport);
 
+    spin_lock(&lchn->lock);
+
     if ( likely(lchn->state == ECS_INTERDOMAIN) )
     {
         ASSERT(consumer_is_xen(lchn));
@@ -1191,7 +1246,7 @@ void notify_via_xen_event_channel(struct domain *ld, int 
lport)
         evtchn_port_set_pending(rd, rchn->notify_vcpu_id, rchn);
     }
 
-    spin_unlock(&ld->event_lock);
+    spin_unlock(&lchn->lock);
 }
 
 void evtchn_check_pollers(struct domain *d, unsigned int port)
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index d810e1c..ce10a66 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -79,6 +79,7 @@ extern domid_t hardware_domid;
 
 struct evtchn
 {
+    spinlock_t lock;
 #define ECS_FREE         0 /* Channel is available for use.                  */
 #define ECS_RESERVED     1 /* Channel is reserved.                           */
 #define ECS_UNBOUND      2 /* Channel is waiting to bind to a remote domain. */
--
generated by git-patchbot for /home/xen/git/xen.git#master

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