diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 7db7723..d56187c 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -299,6 +299,7 @@
 /* Install a pte for a particular vaddr in kernel space. */
 void set_pte_vaddr(unsigned long vaddr, pte_t pte);
 
+extern void native_pagetable_reserve(u64 start, u64 end);
 #ifdef CONFIG_X86_32
 extern void native_pagetable_setup_start(pgd_t *base);
 extern void native_pagetable_setup_done(pgd_t *base);
diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 643ebf2..d3d8590 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -68,6 +68,17 @@
 };
 
 /**
+ * struct x86_init_mapping - platform specific initial kernel pagetable setup
+ * @pagetable_reserve:	reserve a range of addresses for kernel pagetable usage
+ *
+ * For more details on the purpose of this hook, look in
+ * init_memory_mapping and the commit that added it.
+ */
+struct x86_init_mapping {
+	void (*pagetable_reserve)(u64 start, u64 end);
+};
+
+/**
  * struct x86_init_paging - platform specific paging functions
  * @pagetable_setup_start:	platform specific pre paging_init() call
  * @pagetable_setup_done:	platform specific post paging_init() call
@@ -123,6 +134,7 @@
 	struct x86_init_mpparse		mpparse;
 	struct x86_init_irqs		irqs;
 	struct x86_init_oem		oem;
+	struct x86_init_mapping		mapping;
 	struct x86_init_paging		paging;
 	struct x86_init_timers		timers;
 	struct x86_init_iommu		iommu;
diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index c11514e9..75ef4b1 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -61,6 +61,10 @@
 		.banner			= default_banner,
 	},
 
+	.mapping = {
+		.pagetable_reserve		= native_pagetable_reserve,
+	},
+
 	.paging = {
 		.pagetable_setup_start	= native_pagetable_setup_start,
 		.pagetable_setup_done	= native_pagetable_setup_done,
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 286d289..722a4c3 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -81,6 +81,11 @@
 		end, pgt_buf_start << PAGE_SHIFT, pgt_buf_top << PAGE_SHIFT);
 }
 
+void native_pagetable_reserve(u64 start, u64 end)
+{
+	memblock_x86_reserve_range(start, end, "PGTABLE");
+}
+
 struct map_range {
 	unsigned long start;
 	unsigned long end;
@@ -272,9 +277,24 @@
 
 	__flush_tlb_all();
 
+	/*
+	 * Reserve the kernel pagetable pages we used (pgt_buf_start -
+	 * pgt_buf_end) and free the other ones (pgt_buf_end - pgt_buf_top)
+	 * so that they can be reused for other purposes.
+	 *
+	 * On native it just means calling memblock_x86_reserve_range, on Xen it
+	 * also means marking RW the pagetable pages that we allocated before
+	 * but that haven't been used.
+	 *
+	 * In fact on xen we mark RO the whole range pgt_buf_start -
+	 * pgt_buf_top, because we have to make sure that when
+	 * init_memory_mapping reaches the pagetable pages area, it maps
+	 * RO all the pagetable pages, including the ones that are beyond
+	 * pgt_buf_end at that time.
+	 */
 	if (!after_bootmem && pgt_buf_end > pgt_buf_start)
-		memblock_x86_reserve_range(pgt_buf_start << PAGE_SHIFT,
-				 pgt_buf_end << PAGE_SHIFT, "PGTABLE");
+		x86_init.mapping.pagetable_reserve(PFN_PHYS(pgt_buf_start),
+				PFN_PHYS(pgt_buf_end));
 
 	if (!after_bootmem)
 		early_memtest(start, end);
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index cf4ef61..0684f3c 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1275,6 +1275,20 @@
 {
 }
 
+static __init void xen_mapping_pagetable_reserve(u64 start, u64 end)
+{
+	/* reserve the range used */
+	native_pagetable_reserve(start, end);
+
+	/* set as RW the rest */
+	printk(KERN_DEBUG "xen: setting RW the range %llx - %llx\n", end,
+			PFN_PHYS(pgt_buf_top));
+	while (end < PFN_PHYS(pgt_buf_top)) {
+		make_lowmem_page_readwrite(__va(end));
+		end += PAGE_SIZE;
+	}
+}
+
 static void xen_post_allocator_init(void);
 
 static __init void xen_pagetable_setup_done(pgd_t *base)
@@ -2105,6 +2119,7 @@
 
 void __init xen_init_mmu_ops(void)
 {
+	x86_init.mapping.pagetable_reserve = xen_mapping_pagetable_reserve;
 	x86_init.paging.pagetable_setup_start = xen_pagetable_setup_start;
 	x86_init.paging.pagetable_setup_done = xen_pagetable_setup_done;
 	pv_mmu_ops = xen_mmu_ops;