evtchn: arrange for preemption in evtchn_destroy()

Especially closing of fully established interdomain channels can take
quite some time, due to the locking involved. Therefore we shouldn't
assume we can clean up still active ports all in one go. Besides adding
the necessary preemption check, also avoid pointlessly starting from
(or now really ending at) 0; 1 is the lowest numbered port which may
need closing.

Since we're now reducing ->valid_evtchns, free_xen_event_channel(),
and (at least to be on the safe side) notify_via_xen_event_channel()
need to cope with attempts to close / unbind from / send through already
closed (and no longer valid, as per port_is_valid()) ports.

This is part of XSA-344.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 2ddd7986c1cb1b9e4e29eb93a42bce36f118e924..cacede4cf0bbc839ff39c0073f00a93bbb3fda6b 100644 (file)
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -646,7 +646,6 @@ int domain_kill(struct domain *d)
         if ( d->is_dying != DOMDYING_alive )
             return domain_kill(d);
         d->is_dying = DOMDYING_dying;
-        evtchn_destroy(d);
         gnttab_release_mappings(d);
         tmem_destroy(d->tmem_client);
         vnuma_destroy(d->vnuma);
@@ -654,6 +653,9 @@ int domain_kill(struct domain *d)
         d->tmem_client = NULL;
         /* fallthrough */
     case DOMDYING_dying:
+        rc = evtchn_destroy(d);
+        if ( rc )
+            break;
         rc = domain_relinquish_resources(d);
         if ( rc != 0 )
             break;

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index 753950b81a5dbb398e4e80314ec540ea75c9dee6..52ba2b0c0c3334e1306b199c1e7a8ea00a6e9e99 100644 (file)
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -1291,7 +1291,16 @@ int alloc_unbound_xen_event_channel(
 
 void free_xen_event_channel(struct domain *d, int port)
 {
-    BUG_ON(!port_is_valid(d, port));
+    if ( !port_is_valid(d, port) )
+    {
+        /*
+         * Make sure ->is_dying is read /after/ ->valid_evtchns, pairing
+         * with the spin_barrier() and BUG_ON() in evtchn_destroy().
+         */
+        smp_rmb();
+        BUG_ON(!d->is_dying);
+        return;
+    }
 
     evtchn_close(d, port, 0);
 }
@@ -1303,7 +1312,17 @@ void notify_via_xen_event_channel(struct domain *ld, int lport)
     struct domain *rd;
     unsigned long flags;
 
-    ASSERT(port_is_valid(ld, lport));
+    if ( !port_is_valid(ld, lport) )
+    {
+        /*
+         * Make sure ->is_dying is read /after/ ->valid_evtchns, pairing
+         * with the spin_barrier() and BUG_ON() in evtchn_destroy().
+         */
+        smp_rmb();
+        ASSERT(ld->is_dying);
+        return;
+    }
+
     lchn = evtchn_from_port(ld, lport);
 
     spin_lock_irqsave(&lchn->lock, flags);
@@ -1375,8 +1394,7 @@ int evtchn_init(struct domain *d)
     return 0;
 }
 
-
-void evtchn_destroy(struct domain *d)
+int evtchn_destroy(struct domain *d)
 {
     unsigned int i;
 
@@ -1385,14 +1403,29 @@ void evtchn_destroy(struct domain *d)
     spin_barrier(&d->event_lock);
 
     /* Close all existing event channels. */
-    for ( i = 0; port_is_valid(d, i); i++ )
+    for ( i = d->valid_evtchns; --i; )
+    {
         evtchn_close(d, i, 0);
 
+        /*
+         * Avoid preempting when called from domain_create()'s error path,
+         * and don't check too often (choice of frequency is arbitrary).
+         */
+        if ( i && !(i & 0x3f) && d->is_dying != DOMDYING_dead &&
+             hypercall_preempt_check() )
+        {
+            write_atomic(&d->valid_evtchns, i);
+            return -ERESTART;
+        }
+    }
+
     ASSERT(!d->active_evtchns);
 
     clear_global_virq_handlers(d);
 
     evtchn_fifo_destroy(d);
+
+    return 0;
 }
 
 

diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index a8ebfe6d955f7b488b0e0564c22b286f930fb364..46958de3d1bb4c2786d4e962ea8e7f86fce73b3e 100644 (file)
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -135,7 +135,7 @@ struct evtchn
 } __attribute__((aligned(64)));
 
 int  evtchn_init(struct domain *d); /* from domain_create */
-void evtchn_destroy(struct domain *d); /* from domain_kill */
+int  evtchn_destroy(struct domain *d); /* from domain_kill */
 void evtchn_destroy_final(struct domain *d); /* from complete_domain_destroy */
 
 struct waitqueue_vcpu;