x86: make vcpu_reset() preemptible

... as dropping the old page tables may take significant amounts of
time.

This is part of CVE-2013-1918 / XSA-45.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>

2 files changed, 17 insertions, 8 deletions

diff --git a/xen/common/domain.c b/xen/common/domain.c
index ce45d66b45..7cca65507d 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -868,14 +868,18 @@ void domain_unpause_by_systemcontroller(struct domain *d)
         domain_unpause(d);
 }
 
-void vcpu_reset(struct vcpu *v)
+int vcpu_reset(struct vcpu *v)
 {
     struct domain *d = v->domain;
+    int rc;
 
     vcpu_pause(v);
     domain_lock(d);
 
-    arch_vcpu_reset(v);
+    set_bit(_VPF_in_reset, &v->pause_flags);
+    rc = arch_vcpu_reset(v);
+    if ( rc )
+        goto out_unlock;
 
     set_bit(_VPF_down, &v->pause_flags);
 
@@ -891,9 +895,13 @@ void vcpu_reset(struct vcpu *v)
 #endif
     cpumask_clear(v->cpu_affinity_tmp);
     clear_bit(_VPF_blocked, &v->pause_flags);
+    clear_bit(_VPF_in_reset, &v->pause_flags);
 
+ out_unlock:
     domain_unlock(v->domain);
     vcpu_unpause(v);
+
+    return rc;
 }
 
 
diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 73b12c8a4d..1d00cfc95f 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -332,13 +332,15 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
         ret = -EINVAL;
         if ( (d == current->domain) || /* no domain_pause() */
              (vcpu >= d->max_vcpus) || ((v = d->vcpu[vcpu]) == NULL) )
-            goto svc_out;
+            break;
 
         if ( guest_handle_is_null(op->u.vcpucontext.ctxt) )
         {
-            vcpu_reset(v);
-            ret = 0;
-            goto svc_out;
+            ret = vcpu_reset(v);
+            if ( ret == -EAGAIN )
+                ret = hypercall_create_continuation(
+                          __HYPERVISOR_domctl, "h", u_domctl);
+            break;
         }
 
 #ifdef CONFIG_COMPAT
@@ -347,7 +349,7 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
 #endif
         ret = -ENOMEM;
         if ( (c.nat = alloc_vcpu_guest_context()) == NULL )
-            goto svc_out;
+            break;
 
 #ifdef CONFIG_COMPAT
         if ( !is_pv_32on64_vcpu(v) )
@@ -368,7 +370,6 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
             domain_unpause(d);
         }
 
-    svc_out:
         free_vcpu_guest_context(c.nat);
     }
     break;