arch/x86/kernel/smpboot_32.c

/*
 *	x86 SMP booting functions
 *
 *	(c) 1995 Alan Cox, Building #3 <alan@redhat.com>
 *	(c) 1998, 1999, 2000 Ingo Molnar <mingo@redhat.com>
 *
 *	Much of the core SMP work is based on previous work by Thomas Radke, to
 *	whom a great many thanks are extended.
 *
 *	Thanks to Intel for making available several different Pentium,
 *	Pentium Pro and Pentium-II/Xeon MP machines.
 *	Original development of Linux SMP code supported by Caldera.
 *
 *	This code is released under the GNU General Public License version 2 or
 *	later.
 *
 *	Fixes
 *		Felix Koop	:	NR_CPUS used properly
 *		Jose Renau	:	Handle single CPU case.
 *		Alan Cox	:	By repeated request 8) - Total BogoMIPS report.
 *		Greg Wright	:	Fix for kernel stacks panic.
 *		Erich Boleyn	:	MP v1.4 and additional changes.
 *	Matthias Sattler	:	Changes for 2.1 kernel map.
 *	Michel Lespinasse	:	Changes for 2.1 kernel map.
 *	Michael Chastain	:	Change trampoline.S to gnu as.
 *		Alan Cox	:	Dumb bug: 'B' step PPro's are fine
 *		Ingo Molnar	:	Added APIC timers, based on code
 *					from Jose Renau
 *		Ingo Molnar	:	various cleanups and rewrites
 *		Tigran Aivazian	:	fixed "0.00 in /proc/uptime on SMP" bug.
 *	Maciej W. Rozycki	:	Bits for genuine 82489DX APICs
 *		Martin J. Bligh	: 	Added support for multi-quad systems
 *		Dave Jones	:	Report invalid combinations of Athlon CPUs.
*		Rusty Russell	:	Hacked into shape for new "hotplug" boot process. */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/kernel_stat.h>
#include <linux/bootmem.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/percpu.h>
#include <linux/nmi.h>

#include <linux/delay.h>
#include <linux/mc146818rtc.h>
#include <asm/tlbflush.h>
#include <asm/desc.h>
#include <asm/arch_hooks.h>
#include <asm/nmi.h>

#include <mach_apic.h>
#include <mach_wakecpu.h>
#include <smpboot_hooks.h>
#include <asm/vmi.h>
#include <asm/mtrr.h>

/* Set if we find a B stepping CPU */
static int __cpuinitdata smp_b_stepping;

/* Number of siblings per CPU package */
int smp_num_siblings = 1;
EXPORT_SYMBOL(smp_num_siblings);

/* Last level cache ID of each logical CPU */
DEFINE_PER_CPU(u8, cpu_llc_id) = BAD_APICID;

/* representing HT siblings of each logical CPU */
DEFINE_PER_CPU(cpumask_t, cpu_sibling_map);
EXPORT_PER_CPU_SYMBOL(cpu_sibling_map);

/* representing HT and core siblings of each logical CPU */
DEFINE_PER_CPU(cpumask_t, cpu_core_map);
EXPORT_PER_CPU_SYMBOL(cpu_core_map);

/* bitmap of online cpus */
cpumask_t cpu_online_map __read_mostly;
EXPORT_SYMBOL(cpu_online_map);

cpumask_t cpu_callin_map;
cpumask_t cpu_callout_map;
cpumask_t cpu_possible_map;
EXPORT_SYMBOL(cpu_possible_map);
static cpumask_t smp_commenced_mask;

/* Per CPU bogomips and other parameters */
DEFINE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info);
EXPORT_PER_CPU_SYMBOL(cpu_info);

/* which logical CPU number maps to which CPU (physical APIC ID) */
u8 x86_cpu_to_apicid_init[NR_CPUS] __initdata =
			{ [0 ... NR_CPUS-1] = BAD_APICID };
void *x86_cpu_to_apicid_early_ptr;
DEFINE_PER_CPU(u8, x86_cpu_to_apicid) = BAD_APICID;
EXPORT_PER_CPU_SYMBOL(x86_cpu_to_apicid);

u8 apicid_2_node[MAX_APICID];

/*
 * Trampoline 80x86 program as an array.
 */

extern const unsigned char trampoline_data [];
extern const unsigned char trampoline_end  [];
static unsigned char *trampoline_base;

static void map_cpu_to_logical_apicid(void);

/* State of each CPU. */
DEFINE_PER_CPU(int, cpu_state) = { 0 };

/*
 * Currently trivial. Write the real->protected mode
 * bootstrap into the page concerned. The caller
 * has made sure it's suitably aligned.
 */

static unsigned long __cpuinit setup_trampoline(void)
{
	memcpy(trampoline_base, trampoline_data, trampoline_end - trampoline_data);
	return virt_to_phys(trampoline_base);
}

/*
 * We are called very early to get the low memory for the
 * SMP bootup trampoline page.
 */
void __init smp_alloc_memory(void)
{
	trampoline_base = alloc_bootmem_low_pages(PAGE_SIZE);
	/*
	 * Has to be in very low memory so we can execute
	 * real-mode AP code.
	 */
	if (__pa(trampoline_base) >= 0x9F000)
		BUG();
}

/*
 * The bootstrap kernel entry code has set these up. Save them for
 * a given CPU
 */

void __cpuinit smp_store_cpu_info(int id)
{
	struct cpuinfo_x86 *c = &cpu_data(id);

	*c = boot_cpu_data;
	c->cpu_index = id;
	if (id!=0)
		identify_secondary_cpu(c);
	/*
	 * Mask B, Pentium, but not Pentium MMX
	 */
	if (c->x86_vendor == X86_VENDOR_INTEL &&
	    c->x86 == 5 &&
	    c->x86_mask >= 1 && c->x86_mask <= 4 &&
	    c->x86_model <= 3)
		/*
		 * Remember we have B step Pentia with bugs
		 */
		smp_b_stepping = 1;

	/*
	 * Certain Athlons might work (for various values of 'work') in SMP
	 * but they are not certified as MP capable.
	 */
	if ((c->x86_vendor == X86_VENDOR_AMD) && (c->x86 == 6)) {

		if (num_possible_cpus() == 1)
			goto valid_k7;

		/* Athlon 660/661 is valid. */	
		if ((c->x86_model==6) && ((c->x86_mask==0) || (c->x86_mask==1)))
			goto valid_k7;

		/* Duron 670 is valid */
		if ((c->x86_model==7) && (c->x86_mask==0))
			goto valid_k7;

		/*
		 * Athlon 662, Duron 671, and Athlon >model 7 have capability bit.
		 * It's worth noting that the A5 stepping (662) of some Athlon XP's
		 * have the MP bit set.
		 * See http://www.heise.de/newsticker/data/jow-18.10.01-000 for more.
		 */
		if (((c->x86_model==6) && (c->x86_mask>=2)) ||
		    ((c->x86_model==7) && (c->x86_mask>=1)) ||
		     (c->x86_model> 7))
			if (cpu_has_mp)
				goto valid_k7;

		/* If we get here, it's not a certified SMP capable AMD system. */
		add_taint(TAINT_UNSAFE_SMP);
	}

valid_k7:
	;
}

extern void calibrate_delay(void);

static atomic_t init_deasserted;

static void __cpuinit smp_callin(void)
{
	int cpuid, phys_id;
	unsigned long timeout;

	/*
	 * If waken up by an INIT in an 82489DX configuration
	 * we may get here before an INIT-deassert IPI reaches
	 * our local APIC.  We have to wait for the IPI or we'll
	 * lock up on an APIC access.
	 */
	wait_for_init_deassert(&init_deasserted);

	/*
	 * (This works even if the APIC is not enabled.)
	 */
	phys_id = GET_APIC_ID(apic_read(APIC_ID));
	cpuid = smp_processor_id();
	if (cpu_isset(cpuid, cpu_callin_map)) {
		printk("huh, phys CPU#%d, CPU#%d already present??\n",
					phys_id, cpuid);
		BUG();
	}
	Dprintk("CPU#%d (phys ID: %d) waiting for CALLOUT\n", cpuid, phys_id);

	/*
	 * STARTUP IPIs are fragile beasts as they might sometimes
	 * trigger some glue motherboard logic. Complete APIC bus
	 * silence for 1 second, this overestimates the time the
	 * boot CPU is spending to send the up to 2 STARTUP IPIs
	 * by a factor of two. This should be enough.
	 */

	/*
	 * Waiting 2s total for startup (udelay is not yet working)
	 */
	timeout = jiffies + 2*HZ;
	while (time_before(jiffies, timeout)) {
		/*
		 * Has the boot CPU finished it's STARTUP sequence?
		 */
		if (cpu_isset(cpuid, cpu_callout_map))
			break;
		rep_nop();
	}

	if (!time_before(jiffies, timeout)) {
		printk("BUG: CPU%d started up but did not get a callout!\n",
			cpuid);
		BUG();
	}

	/*
	 * the boot CPU has finished the init stage and is spinning
	 * on callin_map until we finish. We are free to set up this
	 * CPU, first the APIC. (this is probably redundant on most
	 * boards)
	 */

	Dprintk("CALLIN, before setup_local_APIC().\n");
	smp_callin_clear_local_apic();
	setup_local_APIC();
	map_cpu_to_logical_apicid();

	/*
	 * Get our bogomips.
	 */
	calibrate_delay();
	Dprintk("Stack at about %p\n",&cpuid);

	/*
	 * Save our processor parameters
	 */
	smp_store_cpu_info(cpuid);

	/*
	 * Allow the master to continue.
	 */
	cpu_set(cpuid, cpu_callin_map);
}

static int cpucount;

/* maps the cpu to the sched domain representing multi-core */
cpumask_t cpu_coregroup_map(int cpu)
{
	struct cpuinfo_x86 *c = &cpu_data(cpu);
	/*
	 * For perf, we return last level cache shared map.
	 * And for power savings, we return cpu_core_map
	 */
	if (sched_mc_power_savings || sched_smt_power_savings)
		return per_cpu(cpu_core_map, cpu);
	else
		return c->llc_shared_map;
}

/* representing cpus for which sibling maps can be computed */
static cpumask_t cpu_sibling_setup_map;

void __cpuinit set_cpu_sibling_map(int cpu)
{
	int i;
	struct cpuinfo_x86 *c = &cpu_data(cpu);

	cpu_set(cpu, cpu_sibling_setup_map);

	if (smp_num_siblings > 1) {
		for_each_cpu_mask(i, cpu_sibling_setup_map) {
			if (c->phys_proc_id == cpu_data(i).phys_proc_id &&
			    c->cpu_core_id == cpu_data(i).cpu_core_id) {
				cpu_set(i, per_cpu(cpu_sibling_map, cpu));
				cpu_set(cpu, per_cpu(cpu_sibling_map, i));
				cpu_set(i, per_cpu(cpu_core_map, cpu));
				cpu_set(cpu, per_cpu(cpu_core_map, i));
				cpu_set(i, c->llc_shared_map);
				cpu_set(cpu, cpu_data(i).llc_shared_map);
			}
		}
	} else {
		cpu_set(cpu, per_cpu(cpu_sibling_map, cpu));
	}

	cpu_set(cpu, c->llc_shared_map);

	if (current_cpu_data.x86_max_cores == 1) {
		per_cpu(cpu_core_map, cpu) = per_cpu(cpu_sibling_map, cpu);
		c->booted_cores = 1;
		return;
	}

	for_each_cpu_mask(i, cpu_sibling_setup_map) {
		if (per_cpu(cpu_llc_id, cpu) != BAD_APICID &&
		    per_cpu(cpu_llc_id, cpu) == per_cpu(cpu_llc_id, i)) {
			cpu_set(i, c->llc_shared_map);
			cpu_set(cpu, cpu_data(i).llc_shared_map);
		}
		if (c->phys_proc_id == cpu_data(i).phys_proc_id) {
			cpu_set(i, per_cpu(cpu_core_map, cpu));
			cpu_set(cpu, per_cpu(cpu_core_map, i));
			/*
			 *  Does this new cpu bringup a new core?
			 */
			if (cpus_weight(per_cpu(cpu_sibling_map, cpu)) == 1) {
				/*
				 * for each core in package, increment
				 * the booted_cores for this new cpu
				 */
				if (first_cpu(per_cpu(cpu_sibling_map, i)) == i)
					c->booted_cores++;
				/*
				 * increment the core count for all
				 * the other cpus in this package
				 */
				if (i != cpu)
					cpu_data(i).booted_cores++;
			} else if (i != cpu && !c->booted_cores)
				c->booted_cores = cpu_data(i).booted_cores;
		}
	}
}

/*
 * Activate a secondary processor.
 */
static void __cpuinit start_secondary(void *unused)
{
	/*
	 * Don't put *anything* before cpu_init(), SMP booting is too
	 * fragile that we want to limit the things done here to the
	 * most necessary things.
	 */
#ifdef CONFIG_VMI
	vmi_bringup();
#endif
	cpu_init();
	preempt_disable();
	smp_callin();
	while (!cpu_isset(smp_processor_id(), smp_commenced_mask))
		rep_nop();
	/*
	 * Check TSC synchronization with the BP:
	 */
	check_tsc_sync_target();

	setup_secondary_clock();
	if (nmi_watchdog == NMI_IO_APIC) {
		disable_8259A_irq(0);
		enable_NMI_through_LVT0();
		enable_8259A_irq(0);
	}
	/*
	 * low-memory mappings have been cleared, flush them from
	 * the local TLBs too.
	 */
	local_flush_tlb();

	/* This must be done before setting cpu_online_map */
	set_cpu_sibling_map(raw_smp_processor_id());
	wmb();

	/*
	 * We need to hold call_lock, so there is no inconsistency
	 * between the time smp_call_function() determines number of
	 * IPI recipients, and the time when the determination is made
	 * for which cpus receive the IPI. Holding this
	 * lock helps us to not include this cpu in a currently in progress
	 * smp_call_function().
	 */
	lock_ipi_call_lock();
	cpu_set(smp_processor_id(), cpu_online_map);
	unlock_ipi_call_lock();
	per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;

	/* We can take interrupts now: we're officially "up". */
	local_irq_enable();

	wmb();
	cpu_idle();
}

/*
 * Everything has been set up for the secondary
 * CPUs - they just need to reload everything
 * from the task structure
 * This function must not return.
 */
void __devinit initialize_secondary(void)
{
	/*
	 * We don't actually need to load the full TSS,
	 * basically just the stack pointer and the ip.
	 */

	asm volatile(
		"movl %0,%%esp\n\t"
		"jmp *%1"
		:
		:"m" (current->thread.sp),"m" (current->thread.ip));
}

/* Static state in head.S used to set up a CPU */
extern struct {
	void * sp;
	unsigned short ss;
} stack_start;

#ifdef CONFIG_NUMA

/* which logical CPUs are on which nodes */
cpumask_t node_to_cpumask_map[MAX_NUMNODES] __read_mostly =
				{ [0 ... MAX_NUMNODES-1] = CPU_MASK_NONE };
EXPORT_SYMBOL(node_to_cpumask_map);
/* which node each logical CPU is on */
int cpu_to_node_map[NR_CPUS] __read_mostly = { [0 ... NR_CPUS-1] = 0 };
EXPORT_SYMBOL(cpu_to_node_map);

/* set up a mapping between cpu and node. */
static inline void map_cpu_to_node(int cpu, int node)
{
	printk("Mapping cpu %d to node %d\n", cpu, node);
	cpu_set(cpu, node_to_cpumask_map[node]);
	cpu_to_node_map[cpu] = node;
}

/* undo a mapping between cpu and node. */
static inline void unmap_cpu_to_node(int cpu)
{
	int node;

	printk("Unmapping cpu %d from all nodes\n", cpu);
	for (node = 0; node < MAX_NUMNODES; node ++)
		cpu_clear(cpu, node_to_cpumask_map[node]);
	cpu_to_node_map[cpu] = 0;
}
#else /* !CONFIG_NUMA */

#define map_cpu_to_node(cpu, node)	({})
#define unmap_cpu_to_node(cpu)	({})

#endif /* CONFIG_NUMA */

u8 cpu_2_logical_apicid[NR_CPUS] __read_mostly = { [0 ... NR_CPUS-1] = BAD_APICID };

static void map_cpu_to_logical_apicid(void)
{
	int cpu = smp_processor_id();
	int apicid = logical_smp_processor_id();
	int node = apicid_to_node(apicid);

	if (!node_online(node))
		node = first_online_node;

	cpu_2_logical_apicid[cpu] = apicid;
	map_cpu_to_node(cpu, node);
}

static void unmap_cpu_to_logical_apicid(int cpu)
{
	cpu_2_logical_apicid[cpu] = BAD_APICID;
	unmap_cpu_to_node(cpu);
}

static inline void __inquire_remote_apic(int apicid)
{
	int i, regs[] = { APIC_ID >> 4, APIC_LVR >> 4, APIC_SPIV >> 4 };
	char *names[] = { "ID", "VERSION", "SPIV" };
	int timeout;
	unsigned long status;

	printk("Inquiring remote APIC #%d...\n", apicid);

	for (i = 0; i < ARRAY_SIZE(regs); i++) {
		printk("... APIC #%d %s: ", apicid, names[i]);

		/*
		 * Wait for idle.
		 */
		status = safe_apic_wait_icr_idle();
		if (status)
			printk("a previous APIC delivery may have failed\n");

		apic_write_around(APIC_ICR2, SET_APIC_DEST_FIELD(apicid));
		apic_write_around(APIC_ICR, APIC_DM_REMRD | regs[i]);

		timeout = 0;
		do {
			udelay(100);
			status = apic_read(APIC_ICR) & APIC_ICR_RR_MASK;
		} while (status == APIC_ICR_RR_INPROG && timeout++ < 1000);

		switch (status) {
		case APIC_ICR_RR_VALID:
			status = apic_read(APIC_RRR);
			printk("%lx\n", status);
			break;
		default:
			printk("failed\n");
		}
	}
}

#ifdef WAKE_SECONDARY_VIA_NMI
/* 
 * Poke the other CPU in the eye via NMI to wake it up. Remember that the normal
 * INIT, INIT, STARTUP sequence will reset the chip hard for us, and this
 * won't ... remember to clear down the APIC, etc later.
 */
static int __devinit
wakeup_secondary_cpu(int logical_apicid, unsigned long start_eip)
{
	unsigned long send_status, accept_status = 0;
	int maxlvt;

	/* Target chip */
	apic_write_around(APIC_ICR2, SET_APIC_DEST_FIELD(logical_apicid));

	/* Boot on the stack */
	/* Kick the second */
	apic_write_around(APIC_ICR, APIC_DM_NMI | APIC_DEST_LOGICAL);

	Dprintk("Waiting for send to finish...\n");
	send_status = safe_apic_wait_icr_idle();

	/*
	 * Give the other CPU some time to accept the IPI.
	 */
	udelay(200);
	/*
	 * Due to the Pentium erratum 3AP.
	 */
	maxlvt = lapic_get_maxlvt();
	if (maxlvt > 3) {
		apic_read_around(APIC_SPIV);
		apic_write(APIC_ESR, 0);
	}
	accept_status = (apic_read(APIC_ESR) & 0xEF);
	Dprintk("NMI sent.\n");

	if (send_status)
		printk("APIC never delivered???\n");
	if (accept_status)
		printk("APIC delivery error (%lx).\n", accept_status);

	return (send_status | accept_status);
}
#endif	/* WAKE_SECONDARY_VIA_NMI */

#ifdef WAKE_SECONDARY_VIA_INIT
static int __devinit
wakeup_secondary_cpu(int phys_apicid, unsigned long start_eip)
{
	unsigned long send_status, accept_status = 0;
	int maxlvt, num_starts, j;

	/*
	 * Be paranoid about clearing APIC errors.
	 */
	if (APIC_INTEGRATED(apic_version[phys_apicid])) {
		apic_read_around(APIC_SPIV);
		apic_write(APIC_ESR, 0);
		apic_read(APIC_ESR);
	}

	Dprintk("Asserting INIT.\n");

	/*
	 * Turn INIT on target chip
	 */
	apic_write_around(APIC_ICR2, SET_APIC_DEST_FIELD(phys_apicid));

	/*
	 * Send IPI
	 */
	apic_write_around(APIC_ICR, APIC_INT_LEVELTRIG | APIC_INT_ASSERT
				| APIC_DM_INIT);

	Dprintk("Waiting for send to finish...\n");
	send_status = safe_apic_wait_icr_idle();

	mdelay(10);

	Dprintk("Deasserting INIT.\n");

	/* Target chip */
	apic_write_around(APIC_ICR2, SET_APIC_DEST_FIELD(phys_apicid));

	/* Send IPI */
	apic_write_around(APIC_ICR, APIC_INT_LEVELTRIG | APIC_DM_INIT);

	Dprintk("Waiting for send to finish...\n");
	send_status = safe_apic_wait_icr_idle();

	atomic_set(&init_deasserted, 1);

	/*
	 * Should we send STARTUP IPIs ?
	 *
	 * Determine this based on the APIC version.
	 * If we don't have an integrated APIC, don't send the STARTUP IPIs.
	 */
	if (APIC_INTEGRATED(apic_version[phys_apicid]))
		num_starts = 2;
	else
		num_starts = 0;

	/*
	 * Paravirt / VMI wants a startup IPI hook here to set up the
	 * target processor state.
	 */
	startup_ipi_hook(phys_apicid, (unsigned long) start_secondary,
		         (unsigned long) stack_start.sp);

	/*
	 * Run STARTUP IPI loop.
	 */
	Dprintk("#startup loops: %d.\n", num_starts);

	maxlvt = lapic_get_maxlvt();

	for (j = 1; j <= num_starts; j++) {
		Dprintk("Sending STARTUP #%d.\n",j);
		apic_read_around(APIC_SPIV);
		apic_write(APIC_ESR, 0);
		apic_read(APIC_ESR);
		Dprintk("After apic_write.\n");

		/*
		 * STARTUP IPI
		 */

		/* Target chip */
		apic_write_around(APIC_ICR2, SET_APIC_DEST_FIELD(phys_apicid));

		/* Boot on the stack */
		/* Kick the second */
		apic_write_around(APIC_ICR, APIC_DM_STARTUP
					| (start_eip >> 12));

		/*
		 * Give the other CPU some time to accept the IPI.
		 */
		udelay(300);

		Dprintk("Startup point 1.\n");

		Dprintk("Waiting for send to finish...\n");
		send_status = safe_apic_wait_icr_idle();

		/*
		 * Give the other CPU some time to accept the IPI.
		 */
		udelay(200);
		/*
		 * Due to the Pentium erratum 3AP.
		 */
		if (maxlvt > 3) {
			apic_read_around(APIC_SPIV);
			apic_write(APIC_ESR, 0);
		}
		accept_status = (apic_read(APIC_ESR) & 0xEF);
		if (send_status || accept_status)
			break;
	}
	Dprintk("After Startup.\n");

	if (send_status)
		printk("APIC never delivered???\n");
	if (accept_status)
		printk("APIC delivery error (%lx).\n", accept_status);

	return (send_status | accept_status);
}
#endif	/* WAKE_SECONDARY_VIA_INIT */

extern cpumask_t cpu_initialized;
static inline int alloc_cpu_id(void)
{
	cpumask_t	tmp_map;
	int cpu;
	cpus_complement(tmp_map, cpu_present_map);
	cpu = first_cpu(tmp_map);
	if (cpu >= NR_CPUS)
		return -ENODEV;
	return cpu;
}

#ifdef CONFIG_HOTPLUG_CPU
static struct task_struct * __cpuinitdata cpu_idle_tasks[NR_CPUS];
static inline struct task_struct * __cpuinit alloc_idle_task(int cpu)
{
	struct task_struct *idle;

	if ((idle = cpu_idle_tasks[cpu]) != NULL) {
		/* initialize thread_struct.  we really want to avoid destroy
		 * idle tread
		 */
		idle->thread.sp = (unsigned long)task_pt_regs(idle);
		init_idle(idle, cpu);
		return idle;
	}
	idle = fork_idle(cpu);

	if (!IS_ERR(idle))
		cpu_idle_tasks[cpu] = idle;
	return idle;
}
#else
#define alloc_idle_task(cpu) fork_idle(cpu)
#endif

static int __cpuinit do_boot_cpu(int apicid, int cpu)
/*
 * NOTE - on most systems this is a PHYSICAL apic ID, but on multiquad
 * (ie clustered apic addressing mode), this is a LOGICAL apic ID.
 * Returns zero if CPU booted OK, else error code from wakeup_secondary_cpu.
 */
{
	struct task_struct *idle;
	unsigned long boot_error;
	int timeout;
	unsigned long start_eip;
	unsigned short nmi_high = 0, nmi_low = 0;

	/*
	 * Save current MTRR state in case it was changed since early boot
	 * (e.g. by the ACPI SMI) to initialize new CPUs with MTRRs in sync:
	 */
	mtrr_save_state();

	/*
	 * We can't use kernel_thread since we must avoid to
	 * reschedule the child.
	 */
	idle = alloc_idle_task(cpu);
	if (IS_ERR(idle))
		panic("failed fork for CPU %d", cpu);

	init_gdt(cpu);
 	per_cpu(current_task, cpu) = idle;
	early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);

	idle->thread.ip = (unsigned long) start_secondary;
	/* start_eip had better be page-aligned! */
	start_eip = setup_trampoline();

	++cpucount;
	alternatives_smp_switch(1);

	/* So we see what's up   */
	printk("Booting processor %d/%d ip %lx\n", cpu, apicid, start_eip);
	/* Stack for startup_32 can be just as for start_secondary onwards */
	stack_start.sp = (void *) idle->thread.sp;

	irq_ctx_init(cpu);

	per_cpu(x86_cpu_to_apicid, cpu) = apicid;
	/*
	 * This grunge runs the startup process for
	 * the targeted processor.
	 */

	atomic_set(&init_deasserted, 0);

	Dprintk("Setting warm reset code and vector.\n");

	store_NMI_vector(&nmi_high, &nmi_low);

	smpboot_setup_warm_reset_vector(start_eip);

	/*
	 * Starting actual IPI sequence...
	 */
	boot_error = wakeup_secondary_cpu(apicid, start_eip);

	if (!boot_error) {
		/*
		 * allow APs to start initializing.
		 */
		Dprintk("Before Callout %d.\n", cpu);
		cpu_set(cpu, cpu_callout_map);
		Dprintk("After Callout %d.\n", cpu);

		/*
		 * Wait 5s total for a response
		 */
		for (timeout = 0; timeout < 50000; timeout++) {
			if (cpu_isset(cpu, cpu_callin_map))
				break;	/* It has booted */
			udelay(100);
		}

		if (cpu_isset(cpu, cpu_callin_map)) {
			/* number CPUs logically, starting from 1 (BSP is 0) */
			Dprintk("OK.\n");
			printk("CPU%d: ", cpu);
			print_cpu_info(&cpu_data(cpu));
			Dprintk("CPU has booted.\n");
		} else {
			boot_error= 1;
			if (*((volatile unsigned char *)trampoline_base)
					== 0xA5)
				/* trampoline started but...? */
				printk("Stuck ??\n");
			else
				/* trampoline code not run */
				printk("Not responding.\n");
			inquire_remote_apic(apicid);
		}
	}

	if (boot_error) {
		/* Try to put things back the way they were before ... */
		unmap_cpu_to_logical_apicid(cpu);
		cpu_clear(cpu, cpu_callout_map); /* was set here (do_boot_cpu()) */
		cpu_clear(cpu, cpu_initialized); /* was set by cpu_init() */
		cpucount--;
	} else {
		per_cpu(x86_cpu_to_apicid, cpu) = apicid;
		cpu_set(cpu, cpu_present_map);
	}

	/* mark "stuck" area as not stuck */
	*((volatile unsigned long *)trampoline_base) = 0;

	return boot_error;
}

#ifdef CONFIG_HOTPLUG_CPU
void cpu_exit_clear(void)
{
	int cpu = raw_smp_processor_id();

	idle_task_exit();

	cpucount --;
	cpu_uninit();
	irq_ctx_exit(cpu);

	cpu_clear(cpu, cpu_callout_map);
	cpu_clear(cpu, cpu_callin_map);

	cpu_clear(cpu, smp_commenced_mask);
	unmap_cpu_to_logical_apicid(cpu);
}

struct warm_boot_cpu_info {
	struct completion *complete;
	struct work_struct task;
	int apicid;
	int cpu;
};

static void __cpuinit do_warm_boot_cpu(struct work_struct *work)
{
	struct warm_boot_cpu_info *info =
		container_of(work, struct warm_boot_cpu_info, task);
	do_boot_cpu(info->apicid, info->cpu);
	complete(info->complete);
}

static int __cpuinit __smp_prepare_cpu(int cpu)
{
	DECLARE_COMPLETION_ONSTACK(done);
	struct warm_boot_cpu_info info;
	int	apicid, ret;

	apicid = per_cpu(x86_cpu_to_apicid, cpu);
	if (apicid == BAD_APICID) {
		ret = -ENODEV;
		goto exit;
	}

	info.complete = &done;
	info.apicid = apicid;
	info.cpu = cpu;
	INIT_WORK(&info.task, do_warm_boot_cpu);

	/* init low mem mapping */
	clone_pgd_range(swapper_pg_dir, swapper_pg_dir + USER_PGD_PTRS,
			min_t(unsigned long, KERNEL_PGD_PTRS, USER_PGD_PTRS));
	flush_tlb_all();
	schedule_work(&info.task);
	wait_for_completion(&done);

	zap_low_mappings();
	ret = 0;
exit:
	return ret;
}
#endif

/*
 * Cycle through the processors sending APIC IPIs to boot each.
 */

static int boot_cpu_logical_apicid;
/* Where the IO area was mapped on multiquad, always 0 otherwise */
void *xquad_portio;
#ifdef CONFIG_X86_NUMAQ
EXPORT_SYMBOL(xquad_portio);
#endif

static void __init smp_boot_cpus(unsigned int max_cpus)
{
	int apicid, cpu, bit, kicked;
	unsigned long bogosum = 0;

	/*
	 * Setup boot CPU information
	 */
	smp_store_cpu_info(0); /* Final full version of the data */
	printk("CPU%d: ", 0);
	print_cpu_info(&cpu_data(0));

	boot_cpu_physical_apicid = GET_APIC_ID(apic_read(APIC_ID));
	boot_cpu_logical_apicid = logical_smp_processor_id();
	per_cpu(x86_cpu_to_apicid, 0) = boot_cpu_physical_apicid;

	current_thread_info()->cpu = 0;

	set_cpu_sibling_map(0);

	/*
	 * If we couldn't find an SMP configuration at boot time,
	 * get out of here now!
	 */
	if (!smp_found_config && !acpi_lapic) {
		printk(KERN_NOTICE "SMP motherboard not detected.\n");
		smpboot_clear_io_apic_irqs();
		phys_cpu_present_map = physid_mask_of_physid(0);
		if (APIC_init_uniprocessor())
			printk(KERN_NOTICE "Local APIC not detected."
					   " Using dummy APIC emulation.\n");
		map_cpu_to_logical_apicid();
		cpu_set(0, per_cpu(cpu_sibling_map, 0));
		cpu_set(0, per_cpu(cpu_core_map, 0));
		return;
	}

	/*
	 * Should not be necessary because the MP table should list the boot
	 * CPU too, but we do it for the sake of robustness anyway.
	 * Makes no sense to do this check in clustered apic mode, so skip it
	 */
	if (!check_phys_apicid_present(boot_cpu_physical_apicid)) {
		printk("weird, boot CPU (#%d) not listed by the BIOS.\n",
				boot_cpu_physical_apicid);
		physid_set(hard_smp_processor_id(), phys_cpu_present_map);
	}

	/*
	 * If we couldn't find a local APIC, then get out of here now!
	 */
	if (APIC_INTEGRATED(apic_version[boot_cpu_physical_apicid]) && !cpu_has_apic) {
		printk(KERN_ERR "BIOS bug, local APIC #%d not detected!...\n",
			boot_cpu_physical_apicid);
		printk(KERN_ERR "... forcing use of dummy APIC emulation. (tell your hw vendor)\n");
		smpboot_clear_io_apic_irqs();
		phys_cpu_present_map = physid_mask_of_physid(0);
		map_cpu_to_logical_apicid();
		cpu_set(0, per_cpu(cpu_sibling_map, 0));
		cpu_set(0, per_cpu(cpu_core_map, 0));
		return;
	}

	verify_local_APIC();

	/*
	 * If SMP should be disabled, then really disable it!
	 */
	if (!max_cpus) {
		smp_found_config = 0;
		printk(KERN_INFO "SMP mode deactivated, forcing use of dummy APIC emulation.\n");

		if (nmi_watchdog == NMI_LOCAL_APIC) {
			printk(KERN_INFO "activating minimal APIC for NMI watchdog use.\n");
			connect_bsp_APIC();
			setup_local_APIC();
		}
		smpboot_clear_io_apic_irqs();
		phys_cpu_present_map = physid_mask_of_physid(0);
		map_cpu_to_logical_apicid();
		cpu_set(0, per_cpu(cpu_sibling_map, 0));
		cpu_set(0, per_cpu(cpu_core_map, 0));
		return;
	}

	connect_bsp_APIC();
	setup_local_APIC();
	map_cpu_to_logical_apicid();


	setup_portio_remap();

	/*
	 * Scan the CPU present map and fire up the other CPUs via do_boot_cpu
	 *
	 * In clustered apic mode, phys_cpu_present_map is a constructed thus:
	 * bits 0-3 are quad0, 4-7 are quad1, etc. A perverse twist on the 
	 * clustered apic ID.
	 */
	Dprintk("CPU present map: %lx\n", physids_coerce(phys_cpu_present_map));

	kicked = 1;
	for (bit = 0; kicked < NR_CPUS && bit < MAX_APICS; bit++) {
		apicid = cpu_present_to_apicid(bit);
		/*
		 * Don't even attempt to start the boot CPU!
		 */
		if ((apicid == boot_cpu_apicid) || (apicid == BAD_APICID))
			continue;

		if (!check_apicid_present(bit))
			continue;
		if (max_cpus <= cpucount+1)
			continue;

		if (((cpu = alloc_cpu_id()) <= 0) || do_boot_cpu(apicid, cpu))
			printk("CPU #%d not responding - cannot use it.\n",
								apicid);
		else
			++kicked;
	}

	/*
	 * Cleanup possible dangling ends...
	 */
	smpboot_restore_warm_reset_vector();

	/*
	 * Allow the user to impress friends.
	 */
	Dprintk("Before bogomips.\n");
	for_each_possible_cpu(cpu)
		if (cpu_isset(cpu, cpu_callout_map))
			bogosum += cpu_data(cpu).loops_per_jiffy;
	printk(KERN_INFO
		"Total of %d processors activated (%lu.%02lu BogoMIPS).\n",
		cpucount+1,
		bogosum/(500000/HZ),
		(bogosum/(5000/HZ))%100);
	
	Dprintk("Before bogocount - setting activated=1.\n");

	if (smp_b_stepping)
		printk(KERN_WARNING "WARNING: SMP operation may be unreliable with B stepping processors.\n");

	/*
	 * Don't taint if we are running SMP kernel on a single non-MP
	 * approved Athlon
	 */
	if (tainted & TAINT_UNSAFE_SMP) {
		if (cpucount)
			printk (KERN_INFO "WARNING: This combination of AMD processors is not suitable for SMP.\n");
		else
			tainted &= ~TAINT_UNSAFE_SMP;
	}

	Dprintk("Boot done.\n");

	/*
	 * construct cpu_sibling_map, so that we can tell sibling CPUs
	 * efficiently.
	 */
	for_each_possible_cpu(cpu) {
		cpus_clear(per_cpu(cpu_sibling_map, cpu));
		cpus_clear(per_cpu(cpu_core_map, cpu));
	}

	cpu_set(0, per_cpu(cpu_sibling_map, 0));
	cpu_set(0, per_cpu(cpu_core_map, 0));

	smpboot_setup_io_apic();

	setup_boot_clock();
}

/* These are wrappers to interface to the new boot process.  Someone
   who understands all this stuff should rewrite it properly. --RR 15/Jul/02 */
void __init native_smp_prepare_cpus(unsigned int max_cpus)
{
	smp_commenced_mask = cpumask_of_cpu(0);
	cpu_callin_map = cpumask_of_cpu(0);
	mb();
	smp_boot_cpus(max_cpus);
}

void __init native_smp_prepare_boot_cpu(void)
{
	unsigned int cpu = smp_processor_id();

	init_gdt(cpu);
	switch_to_new_gdt();

	cpu_set(cpu, cpu_online_map);
	cpu_set(cpu, cpu_callout_map);
	cpu_set(cpu, cpu_present_map);
	cpu_set(cpu, cpu_possible_map);
	__get_cpu_var(cpu_state) = CPU_ONLINE;
}

#ifdef CONFIG_HOTPLUG_CPU
void remove_siblinginfo(int cpu)
{
	int sibling;
	struct cpuinfo_x86 *c = &cpu_data(cpu);

	for_each_cpu_mask(sibling, per_cpu(cpu_core_map, cpu)) {
		cpu_clear(cpu, per_cpu(cpu_core_map, sibling));
		/*/
		 * last thread sibling in this cpu core going down
		 */
		if (cpus_weight(per_cpu(cpu_sibling_map, cpu)) == 1)
			cpu_data(sibling).booted_cores--;
	}
			
	for_each_cpu_mask(sibling, per_cpu(cpu_sibling_map, cpu))
		cpu_clear(cpu, per_cpu(cpu_sibling_map, sibling));
	cpus_clear(per_cpu(cpu_sibling_map, cpu));
	cpus_clear(per_cpu(cpu_core_map, cpu));
	c->phys_proc_id = 0;
	c->cpu_core_id = 0;
	cpu_clear(cpu, cpu_sibling_setup_map);
}

int __cpu_disable(void)
{
	cpumask_t map = cpu_online_map;
	int cpu = smp_processor_id();

	/*
	 * Perhaps use cpufreq to drop frequency, but that could go
	 * into generic code.
 	 *
	 * We won't take down the boot processor on i386 due to some
	 * interrupts only being able to be serviced by the BSP.
	 * Especially so if we're not using an IOAPIC	-zwane
	 */
	if (cpu == 0)
		return -EBUSY;
	if (nmi_watchdog == NMI_LOCAL_APIC)
		stop_apic_nmi_watchdog(NULL);
	clear_local_APIC();
	/* Allow any queued timer interrupts to get serviced */
	local_irq_enable();
	mdelay(1);
	local_irq_disable();

	remove_siblinginfo(cpu);

	cpu_clear(cpu, map);
	fixup_irqs(map);
	/* It's now safe to remove this processor from the online map */
	cpu_clear(cpu, cpu_online_map);
	return 0;
}

void __cpu_die(unsigned int cpu)
{
	/* We don't do anything here: idle task is faking death itself. */
	unsigned int i;

	for (i = 0; i < 10; i++) {
		/* They ack this in play_dead by setting CPU_DEAD */
		if (per_cpu(cpu_state, cpu) == CPU_DEAD) {
			printk ("CPU %d is now offline\n", cpu);
			if (1 == num_online_cpus())
				alternatives_smp_switch(0);
			return;
		}
		msleep(100);
	}
 	printk(KERN_ERR "CPU %u didn't die...\n", cpu);
}
#else /* ... !CONFIG_HOTPLUG_CPU */
int __cpu_disable(void)
{
	return -ENOSYS;
}

void __cpu_die(unsigned int cpu)
{
	/* We said "no" in __cpu_disable */
	BUG();
}
#endif /* CONFIG_HOTPLUG_CPU */

int __cpuinit native_cpu_up(unsigned int cpu)
{
	unsigned long flags;
#ifdef CONFIG_HOTPLUG_CPU
	int ret = 0;

	/*
	 * We do warm boot only on cpus that had booted earlier
	 * Otherwise cold boot is all handled from smp_boot_cpus().
	 * cpu_callin_map is set during AP kickstart process. Its reset
	 * when a cpu is taken offline from cpu_exit_clear().
	 */
	if (!cpu_isset(cpu, cpu_callin_map))
		ret = __smp_prepare_cpu(cpu);

	if (ret)
		return -EIO;
#endif

	/* In case one didn't come up */
	if (!cpu_isset(cpu, cpu_callin_map)) {
		printk(KERN_DEBUG "skipping cpu%d, didn't come online\n", cpu);
		return -EIO;
	}

	per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
	/* Unleash the CPU! */
	cpu_set(cpu, smp_commenced_mask);

	/*
	 * Check TSC synchronization with the AP (keep irqs disabled
	 * while doing so):
	 */
	local_irq_save(flags);
	check_tsc_sync_source(cpu);
	local_irq_restore(flags);

	while (!cpu_isset(cpu, cpu_online_map)) {
		cpu_relax();
		touch_nmi_watchdog();
	}

	return 0;
}

void __init native_smp_cpus_done(unsigned int max_cpus)
{
#ifdef CONFIG_X86_IO_APIC
	setup_ioapic_dest();
#endif
	zap_low_mappings();
}

void __init smp_intr_init(void)
{
	/*
	 * IRQ0 must be given a fixed assignment and initialized,
	 * because it's used before the IO-APIC is set up.
	 */
	set_intr_gate(FIRST_DEVICE_VECTOR, interrupt[0]);

	/*
	 * The reschedule interrupt is a CPU-to-CPU reschedule-helper
	 * IPI, driven by wakeup.
	 */
	set_intr_gate(RESCHEDULE_VECTOR, reschedule_interrupt);

	/* IPI for invalidation */
	set_intr_gate(INVALIDATE_TLB_VECTOR, invalidate_interrupt);

	/* IPI for generic function call */
	set_intr_gate(CALL_FUNCTION_VECTOR, call_function_interrupt);
}

/*
 * If the BIOS enumerates physical processors before logical,
 * maxcpus=N at enumeration-time can be used to disable HT.
 */
static int __init parse_maxcpus(char *arg)
{
	extern unsigned int maxcpus;

	maxcpus = simple_strtoul(arg, NULL, 0);
	return 0;
}
early_param("maxcpus", parse_maxcpus);