[PATCH 2/7] vm-event: VM_EVENT_FLAG_DENY requires VM_EVENT_FLAG_VCPU_PAUSED

[Corneliu ZUZU <czuzu@bitdefender.com>]

For VM_EVENT_FLAG_DENY to work, the vcpu must be paused (sync = 1) until the
vm-event is handled. A vm-event response having VM_EVENT_FLAG_DENY flag set
should also set the VM_EVENT_FLAG_VCPU_PAUSED flag. Enforce that in
vm_event_register_write_resume().

Signed-off-by: Corneliu ZUZU <czuzu@bitdefender.com>
---
 xen/arch/x86/vm_event.c       | 3 ++-
 xen/include/public/vm_event.h | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
index 5635603..75647c4 100644
--- a/xen/arch/x86/vm_event.c
+++ b/xen/arch/x86/vm_event.c
@@ -70,7 +70,8 @@ void vm_event_toggle_singlestep(struct domain *d, struct vcpu *v)
 
 void vm_event_register_write_resume(struct vcpu *v, vm_event_response_t *rsp)
 {
-    if ( rsp->flags & VM_EVENT_FLAG_DENY )
+    if ( (rsp->flags & VM_EVENT_FLAG_DENY) &&
+         (rsp->flags & VM_EVENT_FLAG_VCPU_PAUSED) )
     {
         struct monitor_write_data *w = &v->arch.vm_event->write_data;
 
diff --git a/xen/include/public/vm_event.h b/xen/include/public/vm_event.h
index 586f43b..8f94e20 100644
--- a/xen/include/public/vm_event.h
+++ b/xen/include/public/vm_event.h
@@ -77,6 +77,7 @@
 /*
  * Deny completion of the operation that triggered the event.
  * Currently only useful for MSR and control-register write events.
+ * Requires the vCPU to be paused already (synchronous events only).
  */
 #define VM_EVENT_FLAG_DENY               (1 << 6)
 /*
-- 
2.5.0


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