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>

1 files changed, 6 insertions, 7 deletions

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index bc1a31f7e6..5bf52ff566 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -939,17 +939,16 @@ int arch_set_info_guest(
 #undef c
 }
 
-void arch_vcpu_reset(struct vcpu *v)
+int arch_vcpu_reset(struct vcpu *v)
 {
     if ( !is_hvm_vcpu(v) )
     {
         destroy_gdt(v);
-        vcpu_destroy_pagetables(v, 0);
-    }
-    else
-    {
-        vcpu_end_shutdown_deferral(v);
+        return vcpu_destroy_pagetables(v);
     }
+
+    vcpu_end_shutdown_deferral(v);
+    return 0;
 }
 
 /* 
@@ -1960,7 +1959,7 @@ int domain_relinquish_resources(struct domain *d)
         /* Drop the in-use references to page-table bases. */
         for_each_vcpu ( d, v )
         {
-            ret = vcpu_destroy_pagetables(v, 1);
+            ret = vcpu_destroy_pagetables(v);
             if ( ret )
                 return ret;