x86/mem_sharing: enable mem_sharing on first memop

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>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index da7d142ad8b37e51e1a927f0b1e1b3c58adb69c0..c39e56f5b93d3e9f5518295cb6ee478704b0c833 100644 (file)
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1400,6 +1400,24 @@ 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 -EOPNOTSUPP;
+
+        if ( unlikely(!hap_enabled(d)) )
+            return -ENODEV;
+
+        if ( unlikely(is_iommu_enabled(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;
@@ -1421,10 +1439,8 @@ 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 )
     {
@@ -1432,10 +1448,6 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
     {
         shr_handle_t handle;
 
-        rc = -EINVAL;
-        if ( !mem_sharing_enabled(d) )
-            goto out;
-
         rc = nominate_page(d, _gfn(mso.u.nominate.u.gfn), 0, &handle);
         mso.u.nominate.handle = handle;
     }
@@ -1447,9 +1459,6 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
         gfn_t gfn;
         shr_handle_t handle;
 
-        rc = -EINVAL;
-        if ( !mem_sharing_enabled(d) )
-            goto out;
         rc = mem_sharing_gref_to_gfn(d->grant_table, gref, &gfn, NULL);
         if ( rc < 0 )
             goto out;
@@ -1465,10 +1474,6 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
         struct domain *cd;
         shr_handle_t sh, ch;
 
-        rc = -EINVAL;
-        if ( !mem_sharing_enabled(d) )
-            goto out;
-
         rc = rcu_lock_live_remote_domain_by_id(mso.u.share.client_domain,
                                                &cd);
         if ( rc )
@@ -1535,10 +1540,6 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
         struct domain *cd;
         shr_handle_t sh;
 
-        rc = -EINVAL;
-        if ( !mem_sharing_enabled(d) )
-            goto out;
-
         rc = rcu_lock_live_remote_domain_by_id(mso.u.share.client_domain,
                                                &cd);
         if ( rc )
@@ -1597,9 +1598,6 @@ int mem_sharing_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_sharing_op_t) arg)
               mso.u.range.opaque > mso.u.range.last_gfn) )
             goto out;
 
-        if ( !mem_sharing_enabled(d) )
-            goto out;
-
         rc = rcu_lock_live_remote_domain_by_id(mso.u.range.client_domain,
                                                &cd);
         if ( rc )
@@ -1691,18 +1689,10 @@ 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(is_iommu_enabled(d) && mec->u.enable) )
-            rc = -EXDEV;
-        else
-            d->arch.hvm.mem_sharing_enabled = mec->u.enable;
+        rc = mem_sharing_control(d, mec->u.enable);
         break;
 
     default: