[PATCH 2/3] xen/vm_event: add vm_event_check_pending_op

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

Perform sanity checking when shutting vm_event down to determine whether
it is safe to do so. Error out with -EAGAIN in case pending operations
have been found for the domain.

Signed-off-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
---
 xen/arch/x86/vm_event.c        | 23 +++++++++++++++++++++++
 xen/common/vm_event.c          | 17 ++++++++++++++---
 xen/include/asm-arm/vm_event.h |  7 +++++++
 xen/include/asm-x86/vm_event.h |  2 ++
 4 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
index 848d69c1b0..558b7da4b1 100644
--- a/xen/arch/x86/vm_event.c
+++ b/xen/arch/x86/vm_event.c
@@ -297,6 +297,29 @@ void vm_event_emulate_check(struct vcpu *v, 
vm_event_response_t *rsp)
     };
 }
 
+bool vm_event_check_pending_op(struct vcpu *v)
+{
+    struct monitor_write_data *w = &v->arch.vm_event->write_data;
+
+    if ( !v->arch.vm_event->sync_event )
+        return false;
+
+    if ( w->do_write.cr0 )
+        return true;
+    if ( w->do_write.cr3 )
+        return true;
+    if ( w->do_write.cr4 )
+        return true;
+    if ( w->do_write.msr )
+        return true;
+    if ( v->arch.vm_event->set_gprs )
+        return true;
+    if ( v->arch.vm_event->emulate_flags )
+        return true;
+
+    return false;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/common/vm_event.c b/xen/common/vm_event.c
index 127f2d58f1..2df327a42c 100644
--- a/xen/common/vm_event.c
+++ b/xen/common/vm_event.c
@@ -183,6 +183,7 @@ static int vm_event_disable(struct domain *d, struct 
vm_event_domain **p_ved)
     if ( vm_event_check_ring(ved) )
     {
         struct vcpu *v;
+        bool pending_op = false;
 
         spin_lock(&ved->lock);
 
@@ -192,9 +193,6 @@ static int vm_event_disable(struct domain *d, struct 
vm_event_domain **p_ved)
             return -EBUSY;
         }
 
-        /* Free domU's event channel and leave the other one unbound */
-        free_xen_event_channel(d, ved->xen_port);
-
         /* Unblock all vCPUs */
         for_each_vcpu ( d, v )
         {
@@ -203,8 +201,21 @@ static int vm_event_disable(struct domain *d, struct 
vm_event_domain **p_ved)
                 vcpu_unpause(v);
                 ved->blocked--;
             }
+
+            if ( vm_event_check_pending_op(v) )
+                pending_op = true;
         }
 
+        /* vm_event ops are still pending until vCPUs get scheduled */
+        if ( pending_op )
+        {
+            spin_unlock(&ved->lock);
+            return -EAGAIN;
+        }
+
+        /* Free domU's event channel and leave the other one unbound */
+        free_xen_event_channel(d, ved->xen_port);
+
         destroy_ring_for_helper(&ved->ring_page, ved->ring_pg_struct);
 
         vm_event_cleanup_domain(d);
diff --git a/xen/include/asm-arm/vm_event.h b/xen/include/asm-arm/vm_event.h
index 14d1d341cc..5cbc9c6dc2 100644
--- a/xen/include/asm-arm/vm_event.h
+++ b/xen/include/asm-arm/vm_event.h
@@ -58,4 +58,11 @@ void vm_event_sync_event(struct vcpu *v, bool value)
     /* Not supported on ARM. */
 }
 
+static inline
+bool vm_event_check_pending_op(struct vcpu *v)
+{
+    /* Not supported on ARM. */
+    return false;
+}
+
 #endif /* __ASM_ARM_VM_EVENT_H__ */
diff --git a/xen/include/asm-x86/vm_event.h b/xen/include/asm-x86/vm_event.h
index 785e741fba..9c5ce3129c 100644
--- a/xen/include/asm-x86/vm_event.h
+++ b/xen/include/asm-x86/vm_event.h
@@ -54,4 +54,6 @@ void vm_event_emulate_check(struct vcpu *v, 
vm_event_response_t *rsp);
 
 void vm_event_sync_event(struct vcpu *v, bool value);
 
+bool vm_event_check_pending_op(struct vcpu *v);
+
 #endif /* __ASM_X86_VM_EVENT_H__ */
-- 
2.26.1