adjust a few RCU domain locking calls

x86's do_physdev_op() had a case where the locking was entirely
superfluous. Its physdev_map_pirq() further had a case where the lock
was being obtained too early, needlessly complicating early exit paths.

Grant table code had two open coded instances of
rcu_lock_target_domain_by_id(), and a third code section could be
consolidated by using the newly introduced helper function.

The memory hypercall code had two more instances of open coding
rcu_lock_target_domain_by_id(), but note that here this is not just
cleanup, but also fixes an error return path in memory_exchange() to
actually return an error.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

1 files changed, 36 insertions, 47 deletions

diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index a9864d7db7..b81dcff353 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -24,7 +24,7 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
 
-#include <xen/config.h>
+#include <xen/err.h>
 #include <xen/iocap.h>
 #include <xen/lib.h>
 #include <xen/sched.h>
@@ -195,6 +195,30 @@ double_gt_unlock(struct grant_table *lgt, struct grant_table *rgt)
         spin_unlock(&rgt->lock);
 }
 
+static struct domain *gt_lock_target_domain_by_id(domid_t dom)
+{
+    struct domain *d;
+    int rc = GNTST_general_error;
+
+    switch ( rcu_lock_target_domain_by_id(dom, &d) )
+    {
+    case 0:
+        return d;
+
+    case -ESRCH:
+        gdprintk(XENLOG_INFO, "Bad domid %d.\n", dom);
+        rc = GNTST_bad_domain;
+        break;
+
+    case -EPERM:
+        rc = GNTST_permission_denied;
+        break;
+    }
+
+    ASSERT(rc < 0 && -rc <= MAX_ERRNO);
+    return ERR_PTR(rc);
+}
+
 static inline int
 __get_maptrack_handle(
     struct grant_table *t)
@@ -1261,7 +1285,6 @@ gnttab_setup_table(
     struct grant_table *gt;
     int            i;
     unsigned long  gmfn;
-    domid_t        dom;
 
     if ( count != 1 )
         return -EINVAL;
@@ -1281,25 +1304,11 @@ gnttab_setup_table(
         goto out1;
     }
 
-    dom = op.dom;
-    if ( dom == DOMID_SELF )
+    d = gt_lock_target_domain_by_id(op.dom);
+    if ( IS_ERR(d) )
     {
-        d = rcu_lock_current_domain();
-    }
-    else
-    {
-        if ( unlikely((d = rcu_lock_domain_by_id(dom)) == NULL) )
-        {
-            gdprintk(XENLOG_INFO, "Bad domid %d.\n", dom);
-            op.status = GNTST_bad_domain;
-            goto out1;
-        }
-
-        if ( unlikely(!IS_PRIV_FOR(current->domain, d)) )
-        {
-            op.status = GNTST_permission_denied;
-            goto out2;
-        }
+        op.status = PTR_ERR(d);
+        goto out1;
     }
 
     if ( xsm_grant_setup(current->domain, d) )
@@ -1352,7 +1361,6 @@ gnttab_query_size(
 {
     struct gnttab_query_size op;
     struct domain *d;
-    domid_t        dom;
     int rc;
 
     if ( count != 1 )
@@ -1364,25 +1372,11 @@ gnttab_query_size(
         return -EFAULT;
     }
 
-    dom = op.dom;
-    if ( dom == DOMID_SELF )
-    {
-        d = rcu_lock_current_domain();
-    }
-    else
+    d = gt_lock_target_domain_by_id(op.dom);
+    if ( IS_ERR(d) )
     {
-        if ( unlikely((d = rcu_lock_domain_by_id(dom)) == NULL) )
-        {
-            gdprintk(XENLOG_INFO, "Bad domid %d.\n", dom);
-            op.status = GNTST_bad_domain;
-            goto query_out;
-        }
-
-        if ( unlikely(!IS_PRIV_FOR(current->domain, d)) )
-        {
-            op.status = GNTST_permission_denied;
-            goto query_out_unlock;
-        }
+        op.status = PTR_ERR(d);
+        goto query_out;
     }
 
     rc = xsm_grant_query_size(current->domain, d);
@@ -2251,15 +2245,10 @@ gnttab_get_status_frames(XEN_GUEST_HANDLE(gnttab_get_status_frames_t) uop,
         return -EFAULT;
     }
 
-    rc = rcu_lock_target_domain_by_id(op.dom, &d);
-    if ( rc < 0 )
+    d = gt_lock_target_domain_by_id(op.dom);
+    if ( IS_ERR(d) )
     {
-        if ( rc == -ESRCH )
-            op.status = GNTST_bad_domain;
-        else if ( rc == -EPERM )
-            op.status = GNTST_permission_denied;
-        else
-            op.status = GNTST_general_error;
+        op.status = PTR_ERR(d);
         goto out1;
     }
     rc = xsm_grant_setup(current->domain, d);