linux/arch/x86_64/kernel/smpboot.c

/*
 *	x86 SMP booting functions
 *
 *	(c) 1995 Alan Cox, Building #3 <alan@redhat.com>
 *	(c) 1998, 1999, 2000 Ingo Molnar <mingo@redhat.com>
 *	Copyright 2001 Andi Kleen, SuSE Labs.
 *
 *	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
 *
 *	Fixes
 *		Felix Koop	:	NR_CPUS used properly
 *		Jose Renau	:	Handle single CPU case.
 *		Alan Cox	:	By repeated request 8) - Total BogoMIP 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
 *	Andi Kleen		:	Changed for SMP boot into long mode.
 *		Rusty Russell	:	Hacked into shape for new "hotplug" boot process.
 *      Andi Kleen              :       Converted to new state machine.
 *					Various cleanups.
 *					Probably mostly hotplug CPU ready now.
 */


#include <linux/config.h>
#include <linux/init.h>

#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/smp_lock.h>
#include <linux/irq.h>
#include <linux/bootmem.h>
#include <linux/thread_info.h>
#include <linux/module.h>

#include <linux/delay.h>
#include <linux/mc146818rtc.h>
#include <asm/mtrr.h>
#include <asm/pgalloc.h>
#include <asm/desc.h>
#include <asm/kdebug.h>
#include <asm/tlbflush.h>
#include <asm/proto.h>

/* Change for real CPU hotplug. Note other files need to be fixed
   first too. */
#define __cpuinit __init
#define __cpuinitdata __initdata

/* Number of siblings per CPU package */
int smp_num_siblings = 1;
/* Package ID of each logical CPU */
u8 phys_proc_id[NR_CPUS] = { [0 ... NR_CPUS-1] = BAD_APICID };
u8 cpu_core_id[NR_CPUS] = { [0 ... NR_CPUS-1] = BAD_APICID };
EXPORT_SYMBOL(phys_proc_id);
EXPORT_SYMBOL(cpu_core_id);

/* Bitmask of currently online CPUs */
cpumask_t cpu_online_map;

EXPORT_SYMBOL(cpu_online_map);

/*
 * Private maps to synchronize booting between AP and BP.
 * Probably not needed anymore, but it makes for easier debugging. -AK
 */
cpumask_t cpu_callin_map;
cpumask_t cpu_callout_map;

cpumask_t cpu_possible_map;
EXPORT_SYMBOL(cpu_possible_map);

/* Per CPU bogomips and other parameters */
struct cpuinfo_x86 cpu_data[NR_CPUS] __cacheline_aligned;

/* Set when the idlers are all forked */
int smp_threads_ready;

cpumask_t cpu_sibling_map[NR_CPUS] __cacheline_aligned;
cpumask_t cpu_core_map[NR_CPUS] __cacheline_aligned;

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

extern unsigned char trampoline_data[];
extern unsigned char trampoline_end[];

/*
 * 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)
{
	void *tramp = __va(SMP_TRAMPOLINE_BASE); 
	memcpy(tramp, trampoline_data, trampoline_end - trampoline_data);
	return virt_to_phys(tramp);
}

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

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

	*c = boot_cpu_data;
	identify_cpu(c);
}

/*
 * Synchronize TSCs of CPUs
 *
 * This new algorithm is less accurate than the old "zero TSCs"
 * one, but we cannot zero TSCs anymore in the new hotplug CPU
 * model.
 */

static atomic_t __cpuinitdata tsc_flag;
static __cpuinitdata DEFINE_SPINLOCK(tsc_sync_lock);
static unsigned long long __cpuinitdata bp_tsc, ap_tsc;

#define NR_LOOPS 5

static void __cpuinit sync_tsc_bp_init(int init)
{
	if (init)
		_raw_spin_lock(&tsc_sync_lock);
	else
		_raw_spin_unlock(&tsc_sync_lock);
	atomic_set(&tsc_flag, 0);
}

/*
 * Synchronize TSC on AP with BP.
 */
static void __cpuinit __sync_tsc_ap(void)
{
	if (!cpu_has_tsc)
		return;
	Dprintk("AP %d syncing TSC\n", smp_processor_id());

	while (atomic_read(&tsc_flag) != 0)
		cpu_relax();
	atomic_inc(&tsc_flag);
	mb();
	_raw_spin_lock(&tsc_sync_lock);
	wrmsrl(MSR_IA32_TSC, bp_tsc);
	_raw_spin_unlock(&tsc_sync_lock);
	rdtscll(ap_tsc);
	mb();
	atomic_inc(&tsc_flag);
	mb();
}

static void __cpuinit sync_tsc_ap(void)
{
	int i;
	for (i = 0; i < NR_LOOPS; i++)
		__sync_tsc_ap();
}

/*
 * Synchronize TSC from BP to AP.
 */
static void __cpuinit __sync_tsc_bp(int cpu)
{
	if (!cpu_has_tsc)
		return;

	/* Wait for AP */
	while (atomic_read(&tsc_flag) == 0)
		cpu_relax();
	/* Save BPs TSC */
	sync_core();
	rdtscll(bp_tsc);
	/* Don't do the sync core here to avoid too much latency. */
	mb();
	/* Start the AP */
	_raw_spin_unlock(&tsc_sync_lock);
	/* Wait for AP again */
	while (atomic_read(&tsc_flag) < 2)
		cpu_relax();
	rdtscl(bp_tsc);
	barrier();
}

static void __cpuinit sync_tsc_bp(int cpu)
{
	int i;
	for (i = 0; i < NR_LOOPS - 1; i++) {
		__sync_tsc_bp(cpu);
		sync_tsc_bp_init(1);
	}
	__sync_tsc_bp(cpu);
	printk(KERN_INFO "Synced TSC of CPU %d difference %Ld\n",
	       cpu, ap_tsc - bp_tsc);
}

static atomic_t init_deasserted __cpuinitdata;

/*
 * Report back to the Boot Processor.
 * Running on AP.
 */
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.
	 */
	while (!atomic_read(&init_deasserted))
		cpu_relax();

	/*
	 * (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)) {
		panic("smp_callin: phys CPU#%d, CPU#%d already present??\n",
					phys_id, cpuid);
	}
	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;
		cpu_relax();
	}

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

	/*
	 * 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");
	setup_local_APIC();

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

	disable_APIC_timer();

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

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

/*
 * Setup code on secondary processor (after comming out of the trampoline)
 */
void __cpuinit start_secondary(void)
{
	/*
	 * Dont put anything before smp_callin(), SMP
	 * booting is too fragile that we want to limit the
	 * things done here to the most necessary things.
	 */
	cpu_init();
	smp_callin();

	/*
	 * Synchronize the TSC with the BP
	 */
	sync_tsc_ap();

	/* otherwise gcc will move up the smp_processor_id before the cpu_init */
	barrier();

	Dprintk("cpu %d: setting up apic clock\n", smp_processor_id()); 	
	setup_secondary_APIC_clock();

	Dprintk("cpu %d: enabling apic timer\n", smp_processor_id());

	if (nmi_watchdog == NMI_IO_APIC) {
		disable_8259A_irq(0);
		enable_NMI_through_LVT0(NULL);
		enable_8259A_irq(0);
	}


	enable_APIC_timer();

	/*
	 * Allow the master to continue.
	 */
	cpu_set(smp_processor_id(), cpu_online_map);
	mb();

	cpu_idle();
}

extern volatile unsigned long init_rsp;
extern void (*initial_code)(void);

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

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

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

		/*
		 * Wait for idle.
		 */
		apic_wait_icr_idle();

		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("%08x\n", status);
			break;
		default:
			printk("failed\n");
		}
	}
}
#endif

/*
 * Kick the secondary to wake up.
 */
static int __cpuinit wakeup_secondary_via_INIT(int phys_apicid, unsigned int start_rip)
{
	unsigned long send_status = 0, accept_status = 0;
	int maxlvt, timeout, num_starts, j;

	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");
	timeout = 0;
	do {
		Dprintk("+");
		udelay(100);
		send_status = apic_read(APIC_ICR) & APIC_ICR_BUSY;
	} while (send_status && (timeout++ < 1000));

	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");
	timeout = 0;
	do {
		Dprintk("+");
		udelay(100);
		send_status = apic_read(APIC_ICR) & APIC_ICR_BUSY;
	} while (send_status && (timeout++ < 1000));

	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;

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

	maxlvt = 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_rip >> 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");
		timeout = 0;
		do {
			Dprintk("+");
			udelay(100);
			send_status = apic_read(APIC_ICR) & APIC_ICR_BUSY;
		} while (send_status && (timeout++ < 1000));

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

	return (send_status | accept_status);
}

/*
 * Boot one CPU.
 */
static int __cpuinit do_boot_cpu(int cpu, int apicid)
{
	struct task_struct *idle;
	unsigned long boot_error;
	int timeout;
	unsigned long start_rip;
	/*
	 * We can't use kernel_thread since we must avoid to
	 * reschedule the child.
	 */
	idle = fork_idle(cpu);
	if (IS_ERR(idle)) {
		printk("failed fork for CPU %d\n", cpu);
		return PTR_ERR(idle);
	}
	x86_cpu_to_apicid[cpu] = apicid;

	cpu_pda[cpu].pcurrent = idle;

	start_rip = setup_trampoline();

	init_rsp = idle->thread.rsp;
	per_cpu(init_tss,cpu).rsp0 = init_rsp;
	initial_code = start_secondary;
	clear_ti_thread_flag(idle->thread_info, TIF_FORK);

	printk(KERN_INFO "Booting processor %d/%d rip %lx rsp %lx\n", cpu, apicid,
	       start_rip, init_rsp);

	/*
	 * This grunge runs the startup process for
	 * the targeted processor.
	 */

	atomic_set(&init_deasserted, 0);

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

	CMOS_WRITE(0xa, 0xf);
	local_flush_tlb();
	Dprintk("1.\n");
	*((volatile unsigned short *) phys_to_virt(0x469)) = start_rip >> 4;
	Dprintk("2.\n");
	*((volatile unsigned short *) phys_to_virt(0x467)) = start_rip & 0xf;
	Dprintk("3.\n");

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

	/*
	 * Status is now clean
	 */
	boot_error = 0;

	/*
	 * Starting actual IPI sequence...
	 */
	boot_error = wakeup_secondary_via_INIT(apicid, start_rip);

	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");
			print_cpu_info(&cpu_data[cpu]);
			Dprintk("CPU has booted.\n");
		} else {
			boot_error = 1;
			if (*((volatile unsigned char *)phys_to_virt(SMP_TRAMPOLINE_BASE))
					== 0xA5)
				/* trampoline started but...? */
				printk("Stuck ??\n");
			else
				/* trampoline code not run */
				printk("Not responding.\n");
#if APIC_DEBUG
			inquire_remote_apic(apicid);
#endif
		}
	}
	if (boot_error) {
		cpu_clear(cpu, cpu_callout_map); /* was set here (do_boot_cpu()) */
		clear_bit(cpu, &cpu_initialized); /* was set by cpu_init() */
		cpu_clear(cpu, cpu_present_map);
		cpu_clear(cpu, cpu_possible_map);
		x86_cpu_to_apicid[cpu] = BAD_APICID;
		x86_cpu_to_log_apicid[cpu] = BAD_APICID;
		return -EIO;
	}

	return 0;
}

cycles_t cacheflush_time;
unsigned long cache_decay_ticks;

/*
 * Construct cpu_sibling_map[], so that we can tell the sibling CPU
 * on SMT systems efficiently.
 */
static __cpuinit void detect_siblings(void)
{
	int cpu;

	for (cpu = 0; cpu < NR_CPUS; cpu++) {
		cpus_clear(cpu_sibling_map[cpu]);
		cpus_clear(cpu_core_map[cpu]);
	}

	for_each_online_cpu (cpu) {
		struct cpuinfo_x86 *c = cpu_data + cpu;
		int siblings = 0;
		int i;
		if (smp_num_siblings > 1) {
			for_each_online_cpu (i) {
				if (cpu_core_id[cpu] == phys_proc_id[i]) {
					siblings++;
					cpu_set(i, cpu_sibling_map[cpu]);
				}
			}
		} else {
			siblings++;
			cpu_set(cpu, cpu_sibling_map[cpu]);
		}

		if (siblings != smp_num_siblings) {
			printk(KERN_WARNING
	       "WARNING: %d siblings found for CPU%d, should be %d\n",
			       siblings, cpu, smp_num_siblings);
			smp_num_siblings = siblings;
		}
		if (c->x86_num_cores > 1) {
			for_each_online_cpu(i) {
				if (phys_proc_id[cpu] == phys_proc_id[i])
					cpu_set(i, cpu_core_map[cpu]);
			}
		} else
			cpu_core_map[cpu] = cpu_sibling_map[cpu];
	}
}

/*
 * Cleanup possible dangling ends...
 */
static __cpuinit void smp_cleanup_boot(void)
{
	/*
	 * Paranoid:  Set warm reset code and vector here back
	 * to default values.
	 */
	CMOS_WRITE(0, 0xf);

	/*
	 * Reset trampoline flag
	 */
	*((volatile int *) phys_to_virt(0x467)) = 0;

#ifndef CONFIG_HOTPLUG_CPU
	/*
	 * Free pages reserved for SMP bootup.
	 * When you add hotplug CPU support later remove this
	 * Note there is more work to be done for later CPU bootup.
	 */

	free_page((unsigned long) __va(PAGE_SIZE));
	free_page((unsigned long) __va(SMP_TRAMPOLINE_BASE));
#endif
}

/*
 * Fall back to non SMP mode after errors.
 *
 * RED-PEN audit/test this more. I bet there is more state messed up here.
 */
static __cpuinit void disable_smp(void)
{
	cpu_present_map = cpumask_of_cpu(0);
	cpu_possible_map = cpumask_of_cpu(0);
	if (smp_found_config)
		phys_cpu_present_map = physid_mask_of_physid(boot_cpu_id);
	else
		phys_cpu_present_map = physid_mask_of_physid(0);
	cpu_set(0, cpu_sibling_map[0]);
	cpu_set(0, cpu_core_map[0]);
}

/*
 * Handle user cpus=... parameter.
 */
static __cpuinit void enforce_max_cpus(unsigned max_cpus)
{
	int i, k;
	k = 0;
	for (i = 0; i < NR_CPUS; i++) {
		if (!cpu_possible(i))
			continue;
		if (++k > max_cpus) {
			cpu_clear(i, cpu_possible_map);
			cpu_clear(i, cpu_present_map);
		}
	}
}

/*
 * Various sanity checks.
 */
static int __cpuinit smp_sanity_check(unsigned max_cpus)
{
	if (!physid_isset(hard_smp_processor_id(), phys_cpu_present_map)) {
		printk("weird, boot CPU (#%d) not listed by the BIOS.\n",
		       hard_smp_processor_id());
		physid_set(hard_smp_processor_id(), phys_cpu_present_map);
	}

	/*
	 * If we couldn't find an SMP configuration at boot time,
	 * get out of here now!
	 */
	if (!smp_found_config) {
		printk(KERN_NOTICE "SMP motherboard not detected.\n");
		disable_smp();
		if (APIC_init_uniprocessor())
			printk(KERN_NOTICE "Local APIC not detected."
					   " Using dummy APIC emulation.\n");
		return -1;
	}

	/*
	 * Should not be necessary because the MP table should list the boot
	 * CPU too, but we do it for the sake of robustness anyway.
	 */
	if (!physid_isset(boot_cpu_id, phys_cpu_present_map)) {
		printk(KERN_NOTICE "weird, boot CPU (#%d) not listed by the BIOS.\n",
								 boot_cpu_id);
		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_id]) && !cpu_has_apic) {
		printk(KERN_ERR "BIOS bug, local APIC #%d not detected!...\n",
			boot_cpu_id);
		printk(KERN_ERR "... forcing use of dummy APIC emulation. (tell your hw vendor)\n");
		nr_ioapics = 0;
		return -1;
	}

	/*
	 * If SMP should be disabled, then really disable it!
	 */
	if (!max_cpus) {
		printk(KERN_INFO "SMP mode deactivated, forcing use of dummy APIC emulation.\n");
		nr_ioapics = 0;
		return -1;
	}

	return 0;
}

/*
 * Prepare for SMP bootup.  The MP table or ACPI has been read
 * earlier.  Just do some sanity checking here and enable APIC mode.
 */
void __cpuinit smp_prepare_cpus(unsigned int max_cpus)
{
	int i;

	nmi_watchdog_default();
	current_cpu_data = boot_cpu_data;
	current_thread_info()->cpu = 0;  /* needed? */

	enforce_max_cpus(max_cpus);

	/*
	 * Fill in cpu_present_mask
	 */
	for (i = 0; i < NR_CPUS; i++) {
		int apicid = cpu_present_to_apicid(i);
		if (physid_isset(apicid, phys_cpu_present_map)) {
			cpu_set(i, cpu_present_map);
			/* possible map would be different if we supported real
			   CPU hotplug. */
			cpu_set(i, cpu_possible_map);
		}
	}

	if (smp_sanity_check(max_cpus) < 0) {
		printk(KERN_INFO "SMP disabled\n");
		disable_smp();
		return;
	}


	/*
	 * Switch from PIC to APIC mode.
	 */
	connect_bsp_APIC();
	setup_local_APIC();

	if (GET_APIC_ID(apic_read(APIC_ID)) != boot_cpu_id) {
		panic("Boot APIC ID in local APIC unexpected (%d vs %d)",
		      GET_APIC_ID(apic_read(APIC_ID)), boot_cpu_id);
		/* Or can we switch back to PIC here? */
	}
	x86_cpu_to_apicid[0] = boot_cpu_id;

	/*
	 * Now start the IO-APICs
	 */
	if (!skip_ioapic_setup && nr_ioapics)
		setup_IO_APIC();
	else
		nr_ioapics = 0;

	/*
	 * Set up local APIC timer on boot CPU.
	 */

	setup_boot_APIC_clock();
}

/*
 * Early setup to make printk work.
 */
void __init smp_prepare_boot_cpu(void)
{
	int me = smp_processor_id();
	cpu_set(me, cpu_online_map);
	cpu_set(me, cpu_callout_map);
}

/*
 * Entry point to boot a CPU.
 *
 * This is all __cpuinit, not __devinit for now because we don't support
 * CPU hotplug (yet).
 */
int __cpuinit __cpu_up(unsigned int cpu)
{
	int err;
	int apicid = cpu_present_to_apicid(cpu);

	WARN_ON(irqs_disabled());

	Dprintk("++++++++++++++++++++=_---CPU UP  %u\n", cpu);

	if (apicid == BAD_APICID || apicid == boot_cpu_id ||
	    !physid_isset(apicid, phys_cpu_present_map)) {
		printk("__cpu_up: bad cpu %d\n", cpu);
		return -EINVAL;
	}
	sync_tsc_bp_init(1);

	/* Boot it! */
	err = do_boot_cpu(cpu, apicid);
	if (err < 0) {
		sync_tsc_bp_init(0);
		Dprintk("do_boot_cpu failed %d\n", err);
		return err;
	}

	sync_tsc_bp(cpu);

	/* Unleash the CPU! */
	Dprintk("waiting for cpu %d\n", cpu);

	while (!cpu_isset(cpu, cpu_online_map))
		cpu_relax();
	return 0;
}

/*
 * Finish the SMP boot.
 */
void __cpuinit smp_cpus_done(unsigned int max_cpus)
{
	zap_low_mappings();
	smp_cleanup_boot();

#ifdef CONFIG_X86_IO_APIC
	setup_ioapic_dest();
#endif

	detect_siblings();
	time_init_gtod();
}