[PATCH for-4.22? 6/9] domctl: handle XEN_DOMCTL_getvcpuinfo without acquiring domctl lock

[Jan Beulich <jbeulich@xxxxxxxx>]

Like for XEN_DOMCTL_getdomaininfo there's no need to hold the domctl
lock for XEN_DOMCTL_getvcpuinfo. While moving the code also switch to
using domain_vcpu().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Tentatively-acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -546,6 +546,33 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
     if ( ret )
         goto domctl_out_unlock_rcuonly;
 
+    switch ( op->cmd )
+    {
+    case XEN_DOMCTL_getvcpuinfo:
+    {
+        const struct vcpu *v;
+
+        if ( (v = domain_vcpu(d, op->u.getvcpuinfo.vcpu)) == NULL )
+        {
+            ret = -ENOENT;
+            goto domctl_out_unlock_rcuonly;
+        }
+
+        op->u.getvcpuinfo.online   = !(v->pause_flags & VPF_down);
+        op->u.getvcpuinfo.blocked  = !!(v->pause_flags & VPF_blocked);
+        op->u.getvcpuinfo.running  = v->is_running;
+        op->u.getvcpuinfo.cpu_time = vcpu_runstate_get_running(v);
+        op->u.getvcpuinfo.cpu      = v->processor;
+
+        copyback = true;
+        goto domctl_out_unlock_rcuonly;
+    }
+
+    default:
+        /* Everything else handled further up or further down. */
+        break;
+    }
+
     if ( !domctl_lock_acquire() )
     {
         if ( d && d != dom_io )
@@ -792,28 +819,6 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
         break;
     }
 
-    case XEN_DOMCTL_getvcpuinfo:
-    {
-        const struct vcpu *v;
-
-        ret = -EINVAL;
-        if ( op->u.getvcpuinfo.vcpu >= d->max_vcpus )
-            break;
-
-        ret = -ESRCH;
-        if ( (v = d->vcpu[op->u.getvcpuinfo.vcpu]) == NULL )
-            break;
-
-        op->u.getvcpuinfo.online   = !(v->pause_flags & VPF_down);
-        op->u.getvcpuinfo.blocked  = !!(v->pause_flags & VPF_blocked);
-        op->u.getvcpuinfo.running  = v->is_running;
-        op->u.getvcpuinfo.cpu_time = vcpu_runstate_get_running(v);
-        op->u.getvcpuinfo.cpu      = v->processor;
-        ret = 0;
-        copyback = 1;
-        break;
-    }
-
     case XEN_DOMCTL_max_mem:
     {
         uint64_t new_max = op->u.max_mem.max_memkb >> (PAGE_SHIFT - 10);