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..37b8b0f 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 __init 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 55c965b..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)
@@ -1463,119 +1477,6 @@
 	return ret;
 }
 
-#ifdef CONFIG_X86_64
-static __initdata u64 __last_pgt_set_rw = 0;
-static __initdata u64 __pgt_buf_start = 0;
-static __initdata u64 __pgt_buf_end = 0;
-static __initdata u64 __pgt_buf_top = 0;
-/*
- * As a consequence of the commit:
- * 
- * commit 4b239f458c229de044d6905c2b0f9fe16ed9e01e
- * Author: Yinghai Lu <yinghai@kernel.org>
- * Date:   Fri Dec 17 16:58:28 2010 -0800
- * 
- *     x86-64, mm: Put early page table high
- * 
- * at some point init_memory_mapping is going to reach the pagetable pages
- * area and map those pages too (mapping them as normal memory that falls
- * in the range of addresses passed to init_memory_mapping as argument).
- * Some of those pages are already pagetable pages (they are in the range
- * pgt_buf_start-pgt_buf_end) therefore they are going to be mapped RO and
- * everything is fine.
- * Some of these pages are not pagetable pages yet (they fall in the range
- * pgt_buf_end-pgt_buf_top; for example the page at pgt_buf_end) so they
- * are going to be mapped RW.  When these pages become pagetable pages and
- * are hooked into the pagetable, xen will find that the guest has already
- * a RW mapping of them somewhere and fail the operation.
- * The reason Xen requires pagetables to be RO is that the hypervisor needs
- * to verify that the pagetables are valid before using them. The validation
- * operations are called "pinning".
- * 
- * In order to fix the issue we mark all the pages in the entire range
- * pgt_buf_start-pgt_buf_top as RO, however when the pagetable allocation
- * is completed only the range pgt_buf_start-pgt_buf_end is reserved by
- * init_memory_mapping. Hence the kernel is going to crash as soon as one
- * of the pages in the range pgt_buf_end-pgt_buf_top is reused (b/c those
- * ranges are RO).
- * 
- * For this reason, 'mark_rw_past_pgt' is introduced which is called _after_
- * the init_memory_mapping has completed (in a perfect world we would
- * call this function from init_memory_mapping, but lets ignore that).
- * 
- * Because we are called _after_ init_memory_mapping the pgt_buf_[start,
- * end,top] have all changed to new values (b/c init_memory_mapping
- * is called and setting up another new page-table). Hence, the first time
- * we enter this function, we save away the pgt_buf_start value and update
- * the pgt_buf_[end,top].
- * 
- * When we detect that the "old" pgt_buf_start through pgt_buf_end
- * PFNs have been reserved (so memblock_x86_reserve_range has been called),
- * we immediately set out to RW the "old" pgt_buf_end through pgt_buf_top.
- * 
- * And then we update those "old" pgt_buf_[end|top] with the new ones
- * so that we can redo this on the next pagetable.
- */
-static __init void mark_rw_past_pgt(void) {
-
-	if (pgt_buf_end > pgt_buf_start) {
-		u64 addr, size;
-
-		/* Save it away. */
-		if (!__pgt_buf_start) {
-			__pgt_buf_start = pgt_buf_start;
-			__pgt_buf_end = pgt_buf_end;
-			__pgt_buf_top = pgt_buf_top;
-			return;
-		}
-		/* If we get the range that starts at __pgt_buf_end that means
-		 * the range is reserved, and that in 'init_memory_mapping'
-		 * the 'memblock_x86_reserve_range' has been called with the
-		 * outdated __pgt_buf_start, __pgt_buf_end (the "new"
-		 * pgt_buf_[start|end|top] refer now to a new pagetable.
-		 * Note: we are called _after_ the pgt_buf_[..] have been
-		 * updated.*/
-
-		addr = memblock_x86_find_in_range_size(PFN_PHYS(__pgt_buf_start),
-						       &size, PAGE_SIZE);
-
-		/* Still not reserved, meaning 'memblock_x86_reserve_range'
-		 * hasn't been called yet. Update the _end and _top.*/
-		if (addr == PFN_PHYS(__pgt_buf_start)) {
-			__pgt_buf_end = pgt_buf_end;
-			__pgt_buf_top = pgt_buf_top;
-			return;
-		}
-
-		/* OK, the area is reserved, meaning it is time for us to
-		 * set RW for the old end->top PFNs. */
-
-		/* ..unless we had already done this. */
-		if (__pgt_buf_end == __last_pgt_set_rw)
-			return;
-
-		addr = PFN_PHYS(__pgt_buf_end);
-		
-		/* set as RW the rest */
-		printk(KERN_DEBUG "xen: setting RW the range %llx - %llx\n",
-			PFN_PHYS(__pgt_buf_end), PFN_PHYS(__pgt_buf_top));
-		
-		while (addr < PFN_PHYS(__pgt_buf_top)) {
-			make_lowmem_page_readwrite(__va(addr));
-			addr += PAGE_SIZE;
-		}
-		/* And update everything so that we are ready for the next
-		 * pagetable (the one created for regions past 4GB) */
-		__last_pgt_set_rw = __pgt_buf_end;
-		__pgt_buf_start = pgt_buf_start;
-		__pgt_buf_end = pgt_buf_end;
-		__pgt_buf_top = pgt_buf_top;
-	}
-	return;
-}
-#else
-static __init void mark_rw_past_pgt(void) { }
-#endif
 static void xen_pgd_free(struct mm_struct *mm, pgd_t *pgd)
 {
 #ifdef CONFIG_X86_64
@@ -1602,14 +1503,6 @@
 	unsigned long pfn = pte_pfn(pte);
 
 	/*
-	 * A bit of optimization. We do not need to call the workaround
-	 * when xen_set_pte_init is called with a PTE with 0 as PFN.
-	 * That is b/c the pagetable at that point are just being populated
-	 * with empty values and we can save some cycles by not calling
-	 * the 'memblock' code.*/
-	if (pfn)
-		mark_rw_past_pgt();
-	/*
 	 * If the new pfn is within the range of the newly allocated
 	 * kernel pagetable, and it isn't being mapped into an
 	 * early_ioremap fixmap slot as a freshly allocated page, make sure
@@ -2118,8 +2011,6 @@
 
 static __init void xen_post_allocator_init(void)
 {
-	mark_rw_past_pgt();
-
 #ifdef CONFIG_XEN_DEBUG
 	pv_mmu_ops.make_pte = PV_CALLEE_SAVE(xen_make_pte_debug);
 #endif
@@ -2228,6 +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;