It is wasteful to require separate hypercalls to enable sharing on both the
parent and the client domain during VM forking. To speed things up we enable
sharing on the first memop in case it wasn't already enabled.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@intel.com>
---
 xen/arch/x86/mm/mem_sharing.c | 39 +++++++++++++++++++++--------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index 99f24fcf6c..65aa64be99 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1402,6 +1402,24 @@ static int range_share(struct domain *d, struct domain *cd,
     return rc;
 }
 
+static inline int mem_sharing_control(struct domain *d, bool enable)
+{
+    if ( enable )
+    {
+        if ( unlikely(!is_hvm_domain(d)) )
+            return -ENOSYS;
+
+        if ( unlikely(!hap_enabled(d)) )
+            return -ENODEV;
+
+        if ( unlikely(has_iommu_pt(d)) )
+            return -EXDEV;
+    }
+
+    d->arch.hvm.mem_sharing.enabled = enable;
+    return 0;
+}
+
 int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
 {
     int rc;
@@ -1423,10 +1441,8 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
     if ( rc )
         goto out;
 
-    /* Only HAP is supported */
-    rc = -ENODEV;
-    if ( !mem_sharing_enabled(d) )
-        goto out;
+    if ( !mem_sharing_enabled(d) && (rc = mem_sharing_control(d, true)) )
+        return rc;
 
     switch ( mso.op )
     {
@@ -1675,24 +1691,15 @@ int mem_sharing_domctl(struct domain *d, struct xen_domctl_mem_sharing_op *mec)
 {
     int rc;
 
-    /* Only HAP is supported */
-    if ( !hap_enabled(d) )
-         return -ENODEV;
-
     switch(mec->op)
     {
         case XEN_DOMCTL_MEM_SHARING_CONTROL:
-        {
-            rc = 0;
-            if ( unlikely(has_iommu_pt(d) && mec->u.enable) )
-                rc = -EXDEV;
-            else
-                d->arch.hvm.mem_sharing.enabled = mec->u.enable;
-        }
-        break;
+            rc = mem_sharing_control(d, mec->u.enable);
+            break;
 
         default:
             rc = -ENOSYS;
+            break;
     }
 
     return rc;
-- 
2.20.1


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