diff -r 68b6bf9b5c8b xen/arch/x86/acpi/boot.c
--- a/xen/arch/x86/acpi/boot.c	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/arch/x86/acpi/boot.c	Thu Nov 12 04:08:43 2009 +0800
@@ -81,7 +81,6 @@ u8 acpi_enable_value, acpi_disable_value
 #warning ACPI uses CMPXCHG, i486 and later hardware
 #endif
 
-#define MAX_MADT_ENTRIES	256
 u8 x86_acpiid_to_apicid[MAX_MADT_ENTRIES] =
     {[0 ... MAX_MADT_ENTRIES - 1] = 0xff };
 EXPORT_SYMBOL(x86_acpiid_to_apicid);
diff -r 68b6bf9b5c8b xen/arch/x86/mpparse.c
--- a/xen/arch/x86/mpparse.c	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/arch/x86/mpparse.c	Thu Nov 12 04:08:43 2009 +0800
@@ -35,7 +35,7 @@
 
 /* Have we found an MP table */
 int smp_found_config;
-unsigned int __initdata maxcpus = NR_CPUS;
+unsigned int __devinitdata maxcpus = NR_CPUS;
 
 /*
  * Various Linux-internal data structures created from the
@@ -868,6 +868,20 @@ int __devinit mp_register_lapic (
     return MP_processor_info(&processor);
 }
 
+void mp_unregister_lapic(uint32_t apic_id, uint32_t cpu)
+{
+    if (!cpu || (apic_id == boot_cpu_physical_apicid))
+        return;
+
+    if (x86_cpu_to_apicid[cpu] != apic_id)
+        return;
+
+    physid_clear(apic_id, phys_cpu_present_map);
+
+    x86_cpu_to_apicid[cpu] = BAD_APICID;
+    cpu_clear(cpu, cpu_present_map);
+ }
+
 #ifdef	CONFIG_X86_IO_APIC
 
 #define MP_ISA_BUS		0
diff -r 68b6bf9b5c8b xen/arch/x86/numa.c
--- a/xen/arch/x86/numa.c	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/arch/x86/numa.c	Thu Nov 12 04:08:43 2009 +0800
@@ -42,9 +42,9 @@ nodemask_t __read_mostly node_online_map
 nodemask_t __read_mostly node_online_map = { { [0] = 1UL } };
 
 /* Default NUMA to off for now. acpi=on required to enable it. */
-int numa_off __initdata = 1;
-
-int acpi_numa __initdata;
+int numa_off __devinitdata = 1;
+
+int acpi_numa __devinitdata;
 
 /*
  * Given a shift value, try to populate memnodemap[]
@@ -53,7 +53,7 @@ int acpi_numa __initdata;
  * 0 if memnodmap[] too small (of shift too small)
  * -1 if node overlap or lost ram (shift too big)
  */
-static int __init
+static int __devinit
 populate_memnodemap(const struct node *nodes, int numnodes, int shift)
 {
 	int i; 
@@ -259,7 +259,7 @@ static __init int numa_setup(char *opt)
  * prior to this call, and this initialization is good enough
  * for the fake NUMA cases.
  */
-void __init init_cpu_to_node(void)
+void __devinit init_cpu_to_node(void)
 {
 	int i;
  	for (i = 0; i < NR_CPUS; i++) {
diff -r 68b6bf9b5c8b xen/arch/x86/platform_hypercall.c
--- a/xen/arch/x86/platform_hypercall.c	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/arch/x86/platform_hypercall.c	Thu Nov 12 04:08:43 2009 +0800
@@ -463,6 +463,12 @@ ret_t do_platform_op(XEN_GUEST_HANDLE(xe
     }
     break;
 
+    case XENPF_cpu_hotadd:
+        ret = cpu_add(op->u.cpu_add.apic_id,
+                      op->u.cpu_add.acpi_id,
+                      op->u.cpu_add.pxm);
+    break;
+
     default:
         ret = -ENOSYS;
         break;
diff -r 68b6bf9b5c8b xen/arch/x86/setup.c
--- a/xen/arch/x86/setup.c	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/arch/x86/setup.c	Thu Nov 12 04:08:43 2009 +0800
@@ -246,7 +246,7 @@ static void __init init_idle_domain(void
     setup_idle_pagetable();
 }
 
-static void __init srat_detect_node(int cpu)
+void __devinit srat_detect_node(int cpu)
 {
     unsigned node;
     u32 apicid = x86_cpu_to_apicid[cpu];
@@ -483,6 +483,10 @@ void __init __start_xen(unsigned long mb
     asm volatile ( "mov %%cr4,%0" : "=r" (this_cpu(cr4)) );
 
     smp_prepare_boot_cpu();
+
+#ifdef CONFIG_HOTPLUG_CPU
+    prefill_possible_map();
+#endif
 
     /* We initialise the serial devices very early so we can get debugging. */
     ns16550.io_base = 0x3f8;
diff -r 68b6bf9b5c8b xen/arch/x86/smpboot.c
--- a/xen/arch/x86/smpboot.c	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/arch/x86/smpboot.c	Thu Nov 12 04:08:43 2009 +0800
@@ -1435,6 +1435,78 @@ void enable_nonboot_cpus(void)
 	 */
 	smpboot_restore_warm_reset_vector();
 }
+
+int prefill_possible_map(void)
+{
+   int i;
+
+   for (i = 0; i < NR_CPUS; i++)
+       cpu_set(i, cpu_possible_map);
+   return 0;
+}
+
+int cpu_add(uint32_t apic_id, uint32_t acpi_id, uint32_t pxm)
+{
+    int cpu = -1;
+
+#ifndef CONFIG_ACPI
+    return -ENOSYS;
+#endif
+
+    dprintk(XENLOG_DEBUG, "cpu_add apic_id %x acpi_id %x pxm %x\n",
+             apic_id, acpi_id, pxm);
+
+    if ( acpi_id > MAX_MADT_ENTRIES || apic_id > MAX_APICS || pxm > 256 )
+        return -EINVAL;
+
+    /* Detect if the cpu has been added before */
+    if ( x86_acpiid_to_apicid[acpi_id] != 0xff)
+    {
+        if (x86_acpiid_to_apicid[acpi_id] != apic_id)
+            return -EINVAL;
+        else
+            return -EEXIST;
+    }
+
+    if ( physid_isset(apic_id, phys_cpu_present_map) )
+        return -EEXIST;
+
+	spin_lock(&cpu_add_remove_lock);
+
+    cpu = mp_register_lapic(apic_id, 1);
+
+    if (cpu < 0)
+    {
+        spin_unlock(&cpu_add_remove_lock);
+        return cpu;
+    }
+
+    x86_acpiid_to_apicid[acpi_id] = apic_id;
+
+    if ( !srat_disabled() )
+    {
+        int node;
+
+        node = setup_node(pxm);
+        if (node < 0)
+        {
+            dprintk(XENLOG_WARNING, "Setup node failed for pxm %x\n", pxm);
+            x86_acpiid_to_apicid[acpi_id] = 0xff;
+            mp_unregister_lapic(apic_id, cpu);
+            spin_unlock(&cpu_add_remove_lock);
+            return node;
+        }
+        apicid_to_node[apic_id] = node;
+    }
+
+    srat_detect_node(cpu);
+    numa_add_cpu(cpu);
+    spin_unlock(&cpu_add_remove_lock);
+    dprintk(XENLOG_INFO, "Add CPU %x with index %x\n", apic_id, cpu);
+    return cpu;
+}
+
+
 #else /* ... !CONFIG_HOTPLUG_CPU */
 int __cpu_disable(void)
 {
@@ -1445,6 +1517,11 @@ void __cpu_die(unsigned int cpu)
 {
 	/* We said "no" in __cpu_disable */
 	BUG();
+}
+
+int cpu_add(uint32_t apic_id, uint32_t acpi_id, uint32_t pxm)
+{
+    return -ENOSYS;
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
diff -r 68b6bf9b5c8b xen/arch/x86/srat.c
--- a/xen/arch/x86/srat.c	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/arch/x86/srat.c	Thu Nov 12 04:08:43 2009 +0800
@@ -41,7 +41,7 @@ int pxm_to_node(int pxm)
 	return (signed char)pxm2node[pxm];
 }
 
-static __init int setup_node(int pxm)
+__devinit int setup_node(int pxm)
 {
 	unsigned node = pxm2node[pxm];
 	if (node == 0xff) {
@@ -91,11 +91,6 @@ static __init void bad_srat(void)
 	acpi_numa = -1;
 	for (i = 0; i < MAX_LOCAL_APIC; i++)
 		apicid_to_node[i] = NUMA_NO_NODE;
-}
-
-static __init inline int srat_disabled(void)
-{
-	return numa_off || acpi_numa < 0;
 }
 
 /*
diff -r 68b6bf9b5c8b xen/include/asm-x86/acpi.h
--- a/xen/include/asm-x86/acpi.h	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/include/asm-x86/acpi.h	Thu Nov 12 04:08:43 2009 +0800
@@ -150,6 +150,7 @@ struct acpi_sleep_info {
 
 #endif /* CONFIG_ACPI_SLEEP */
 
+#define MAX_MADT_ENTRIES	256
 extern u8 x86_acpiid_to_apicid[];
 #define MAX_LOCAL_APIC 256
 
diff -r 68b6bf9b5c8b xen/include/asm-x86/numa.h
--- a/xen/include/asm-x86/numa.h	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/include/asm-x86/numa.h	Thu Nov 12 04:08:43 2009 +0800
@@ -30,7 +30,13 @@ extern void numa_init_array(void);
 extern void numa_init_array(void);
 extern int numa_off;
 
+static __devinit inline int srat_disabled(void)
+{
+	return numa_off || acpi_numa < 0;
+}
 extern void numa_set_node(int cpu, int node);
+extern int setup_node(int pxm);
+extern void srat_detect_node(int cpu);
 
 extern void setup_node_bootmem(int nodeid, u64 start, u64 end);
 extern unsigned char apicid_to_node[256];
diff -r 68b6bf9b5c8b xen/include/asm-x86/smp.h
--- a/xen/include/asm-x86/smp.h	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/include/asm-x86/smp.h	Thu Nov 12 04:08:43 2009 +0800
@@ -66,6 +66,8 @@ extern void cpu_uninit(void);
 extern void cpu_uninit(void);
 extern void disable_nonboot_cpus(void);
 extern void enable_nonboot_cpus(void);
+int prefill_possible_map(void);
+int cpu_add(uint32_t apic_id, uint32_t acpi_id, uint32_t pxm);
 #else
 static inline int cpu_is_offline(int cpu) {return 0;}
 static inline void disable_nonboot_cpus(void) {}
diff -r 68b6bf9b5c8b xen/include/public/platform.h
--- a/xen/include/public/platform.h	Thu Nov 12 04:08:25 2009 +0800
+++ b/xen/include/public/platform.h	Thu Nov 12 04:08:43 2009 +0800
@@ -338,6 +338,14 @@ typedef struct xenpf_cpu_ol xenpf_cpu_ol
 typedef struct xenpf_cpu_ol xenpf_cpu_ol_t;
 DEFINE_XEN_GUEST_HANDLE(xenpf_cpu_ol_t);
 
+#define XENPF_cpu_hotadd    58
+struct xenpf_cpu_hotadd
+{
+	uint32_t apic_id;
+	uint32_t acpi_id;
+	uint32_t pxm;
+};
+
 struct xen_platform_op {
     uint32_t cmd;
     uint32_t interface_version; /* XENPF_INTERFACE_VERSION */
@@ -355,6 +363,7 @@ struct xen_platform_op {
         struct xenpf_set_processor_pminfo set_pminfo;
         struct xenpf_pcpuinfo          pcpu_info;
         struct xenpf_cpu_ol            cpu_ol;
+        struct xenpf_cpu_hotadd        cpu_add;
         uint8_t                        pad[128];
     } u;
 };