diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 02c710bebf7a..44dcad43989d 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1021,10 +1021,6 @@ static void xen_reboot(int reason)
 {
 	struct sched_shutdown r = { .reason = reason };
 
-#ifdef CONFIG_SMP
-	stop_other_cpus();
-#endif
-
 	if (HYPERVISOR_sched_op(SCHEDOP_shutdown, &r))
 		BUG();
 }
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 01afd8a94607..b5a7f928234b 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -181,24 +181,21 @@ char * __init xen_memory_setup(void)
 	for (i = 0; i < memmap.nr_entries; i++) {
 		unsigned long long end = map[i].addr + map[i].size;
 
-		if (map[i].type == E820_RAM) {
-			if (map[i].addr < mem_end && end > mem_end) {
-				/* Truncate region to max_mem. */
-				u64 delta = end - mem_end;
+		if (map[i].type == E820_RAM && end > mem_end) {
+			/* RAM off the end - may be partially included */
+			u64 delta = min(map[i].size, end - mem_end);
 
-				map[i].size -= delta;
-				extra_pages += PFN_DOWN(delta);
+			map[i].size -= delta;
+			end -= delta;
 
-				end = mem_end;
-			}
+			extra_pages += PFN_DOWN(delta);
 		}
 
-		if (end > xen_extra_mem_start)
+		if (map[i].size > 0 && end > xen_extra_mem_start)
 			xen_extra_mem_start = end;
 
-		/* If region is non-RAM or below mem_end, add what remains */
-		if ((map[i].type != E820_RAM || map[i].addr < mem_end) &&
-		    map[i].size > 0)
+		/* Add region if any remains */
+		if (map[i].size > 0)
 			e820_add_region(map[i].addr, map[i].size, map[i].type);
 	}
 
@@ -252,20 +249,6 @@ char * __init xen_memory_setup(void)
 	return "Xen";
 }
 
-static void xen_idle(void)
-{
-	local_irq_disable();
-
-	if (need_resched())
-		local_irq_enable();
-	else {
-		current_thread_info()->status &= ~TS_POLLING;
-		smp_mb__after_clear_bit();
-		safe_halt();
-		current_thread_info()->status |= TS_POLLING;
-	}
-}
-
 /*
  * Set the bit indicating "nosegneg" library variants should be used.
  * We only need to bother in pure 32-bit mode; compat 32-bit processes
@@ -362,7 +345,11 @@ void __init xen_arch_setup(void)
 	       MAX_GUEST_CMDLINE > COMMAND_LINE_SIZE ?
 	       COMMAND_LINE_SIZE : MAX_GUEST_CMDLINE);
 
-	pm_idle = xen_idle;
+	/* Set up idle, making sure it calls safe_halt() pvop */
+#ifdef CONFIG_X86_32
+	boot_cpu_data.hlt_works_ok = 1;
+#endif
+	pm_idle = default_idle;
 
 	fiddle_vdso();
 }
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 2b17ad5b4b32..43f9f02c7db0 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -412,8 +412,16 @@ static int __init balloon_init(void)
 
 	register_balloon(&balloon_sysdev);
 
-	/* Initialise the balloon with excess memory space. */
-	extra_pfn_end = min(e820_end_of_ram_pfn(),
+	/*
+	 * Initialise the balloon with excess memory space.  We need
+	 * to make sure we don't add memory which doesn't exist or
+	 * logically exist.  The E820 map can be trimmed to be smaller
+	 * than the amount of physical memory due to the mem= command
+	 * line parameter.  And if this is a 32-bit non-HIGHMEM kernel
+	 * on a system with memory which requires highmem to access,
+	 * don't try to use it.
+	 */
+	extra_pfn_end = min(min(max_pfn, e820_end_of_ram_pfn()),
 			    (unsigned long)PFN_DOWN(xen_extra_mem_start + xen_extra_mem_size));
 	for (pfn = PFN_UP(xen_extra_mem_start);
 	     pfn < extra_pfn_end;
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 2811bb988ea0..0009e489272c 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -423,7 +423,7 @@ static int find_unbound_irq(void)
 	if (irq == start)
 		goto no_irqs;
 
-	res = irq_alloc_desc_at(irq, 0);
+	res = irq_alloc_desc_at(irq, -1);
 
 	if (WARN_ON(res != irq))
 		return -1;
@@ -630,7 +630,7 @@ int xen_map_pirq_gsi(unsigned pirq, unsigned gsi, int shareable, char *name)
 	if (identity_mapped_irq(gsi) || (!xen_initial_domain() &&
 				xen_pv_domain())) {
 		irq = gsi;
-		irq_alloc_desc_at(irq, 0);
+		irq_alloc_desc_at(irq, -1);
 	} else
 		irq = find_unbound_irq();