diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index f5e86ee..e8e3493 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1408,7 +1408,6 @@ static void __xen_write_cr3(bool kernel, unsigned long cr3)
 		xen_mc_callback(set_current_cr3, (void *)cr3);
 	}
 }
-
 static void xen_write_cr3(unsigned long cr3)
 {
 	BUG_ON(preemptible());
@@ -1434,6 +1433,45 @@ static void xen_write_cr3(unsigned long cr3)
 	xen_mc_issue(PARAVIRT_LAZY_CPU);  /* interrupts restored */
 }
 
+#ifdef CONFIG_X86_64
+/*
+ * At the start of the day - when Xen launches a guest, it has already
+ * built pagetables for the guest. We diligently look over them
+ * in xen_setup_kernel_pagetable and graft as appropiate them in the
+ * init_level4_pgt and its friends. Then when we are happy we load
+ * the new init_level4_pgt - and continue on.
+ *
+ * The generic code starts (start_kernel) and 'init_mem_mapping' sets
+ * up the rest of the pagetables. When it has completed it loads the cr3.
+ * N.B. that baremetal would start at 'start_kernel' (and the early
+ * #PF handler would create bootstrap pagetables) - so we are running
+ * with the same assumptions as what to do when write_cr3 is executed
+ * at this point.
+ *
+ * Since there are no user-page tables at all, we have two variants
+ * of xen_write_cr3 - the early bootup (this one), and the late one
+ * (xen_write_cr3). The reason we have to do that is that in 64-bit
+ * the Linux kernel and user-space are both in ring 3 while the
+ * hypervisor is in ring 0.
+ */
+static void __init xen_write_cr3_init(unsigned long cr3)
+{
+	BUG_ON(preemptible());
+
+	xen_mc_batch();  /* disables interrupts */
+
+	/* Update while interrupts are disabled, so its atomic with
+	   respect to ipis */
+	this_cpu_write(xen_cr3, cr3);
+
+	__xen_write_cr3(true, cr3);
+
+	xen_mc_issue(PARAVIRT_LAZY_CPU);  /* interrupts restored */
+
+	pv_mmu_ops.write_cr3 = &xen_write_cr3;
+}
+#endif
+
 static int xen_pgd_alloc(struct mm_struct *mm)
 {
 	pgd_t *pgd = mm->pgd;
@@ -2102,11 +2140,7 @@ static const struct pv_mmu_ops xen_mmu_ops __initconst = {
 	.write_cr2 = xen_write_cr2,
 
 	.read_cr3 = xen_read_cr3,
-#ifdef CONFIG_X86_32
 	.write_cr3 = xen_write_cr3_init,
-#else
-	.write_cr3 = xen_write_cr3,
-#endif
 
 	.flush_tlb_user = xen_flush_tlb,
 	.flush_tlb_kernel = xen_flush_tlb,