xen: fix 32-bit build resulting from mmu move

Moving the mmu code from enlighten.c to mmu.c inadvertently broke the
32-bit build.  Fix it.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/xen/mmu.c

@@ -1396,6 +1396,43 @@ static void xen_pgd_free(struct mm_struct *mm, pgd_t *pgd)
 #endif
 }
 
+#ifdef CONFIG_HIGHPTE
+static void *xen_kmap_atomic_pte(struct page *page, enum km_type type)
+{
+	pgprot_t prot = PAGE_KERNEL;
+
+	if (PagePinned(page))
+		prot = PAGE_KERNEL_RO;
+
+	if (0 && PageHighMem(page))
+		printk("mapping highpte %lx type %d prot %s\n",
+		       page_to_pfn(page), type,
+		       (unsigned long)pgprot_val(prot) & _PAGE_RW ? "WRITE" : "READ");
+
+	return kmap_atomic_prot(page, type, prot);
+}
+#endif
+
+#ifdef CONFIG_X86_32
+static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte)
+{
+	/* If there's an existing pte, then don't allow _PAGE_RW to be set */
+	if (pte_val_ma(*ptep) & _PAGE_PRESENT)
+		pte = __pte_ma(((pte_val_ma(*ptep) & _PAGE_RW) | ~_PAGE_RW) &
+			       pte_val_ma(pte));
+
+	return pte;
+}
+
+/* Init-time set_pte while constructing initial pagetables, which
+   doesn't allow RO pagetable pages to be remapped RW */
+static __init void xen_set_pte_init(pte_t *ptep, pte_t pte)
+{
+	pte = mask_rw_pte(ptep, pte);
+
+	xen_set_pte(ptep, pte);
+}
+#endif
 
 /* Early in boot, while setting up the initial pagetable, assume
    everything is pinned. */