smp.c

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/*
 *  Intel SMP support routines.
 *
 *  (c) 1995 Alan Cox, Building #3 <[email protected]>
 *  (c) 1998-99, 2000, 2009 Ingo Molnar <[email protected]>
 *      (c) 2002,2003 Andi Kleen, SuSE Labs.
 *
 *  i386 and x86_64 integration by Glauber Costa <[email protected]>
 *
 *  This code is released under the GNU General Public License version 2 or
 *  later.
 */

#include <linux/init.h>

#include <linux/mm.h>
#include <linux/delay.h>
#include <linux/spinlock.h>
#include <linux/export.h>
#include <linux/kernel_stat.h>
#include <linux/mc146818rtc.h>
#include <linux/cache.h>
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/gfp.h>

#include <asm/mtrr.h>
#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include <asm/proto.h>
#include <asm/apic.h>
#include <asm/nmi.h>
/*
 *  Some notes on x86 processor bugs affecting SMP operation:
 *
 *  Pentium, Pentium Pro, II, III (and all CPUs) have bugs.
 *  The Linux implications for SMP are handled as follows:
 *
 *  Pentium III / [Xeon]
 *      None of the E1AP-E3AP errata are visible to the user.
 *
 *  E1AP.   see PII A1AP
 *  E2AP.   see PII A2AP
 *  E3AP.   see PII A3AP
 *
 *  Pentium II / [Xeon]
 *      None of the A1AP-A3AP errata are visible to the user.
 *
 *  A1AP.   see PPro 1AP
 *  A2AP.   see PPro 2AP
 *  A3AP.   see PPro 7AP
 *
 *  Pentium Pro
 *      None of 1AP-9AP errata are visible to the normal user,
 *  except occasional delivery of 'spurious interrupt' as trap #15.
 *  This is very rare and a non-problem.
 *
 *  1AP.    Linux maps APIC as non-cacheable
 *  2AP.    worked around in hardware
 *  3AP.    fixed in C0 and above steppings microcode update.
 *      Linux does not use excessive STARTUP_IPIs.
 *  4AP.    worked around in hardware
 *  5AP.    symmetric IO mode (normal Linux operation) not affected.
 *      'noapic' mode has vector 0xf filled out properly.
 *  6AP.    'noapic' mode might be affected - fixed in later steppings
 *  7AP.    We do not assume writes to the LVT deassering IRQs
 *  8AP.    We do not enable low power mode (deep sleep) during MP bootup
 *  9AP.    We do not use mixed mode
 *
 *  Pentium
 *      There is a marginal case where REP MOVS on 100MHz SMP
 *  machines with B stepping processors can fail. XXX should provide
 *  an L1cache=Writethrough or L1cache=off option.
 *
 *      B stepping CPUs may hang. There are hardware work arounds
 *  for this. We warn about it in case your board doesn't have the work
 *  arounds. Basically that's so I can tell anyone with a B stepping
 *  CPU and SMP problems "tough".
 *
 *  Specific items [From Pentium Processor Specification Update]
 *
 *  1AP.    Linux doesn't use remote read
 *  2AP.    Linux doesn't trust APIC errors
 *  3AP.    We work around this
 *  4AP.    Linux never generated 3 interrupts of the same priority
 *      to cause a lost local interrupt.
 *  5AP.    Remote read is never used
 *  6AP.    not affected - worked around in hardware
 *  7AP.    not affected - worked around in hardware
 *  8AP.    worked around in hardware - we get explicit CS errors if not
 *  9AP.    only 'noapic' mode affected. Might generate spurious
 *      interrupts, we log only the first one and count the
 *      rest silently.
 *  10AP.   not affected - worked around in hardware
 *  11AP.   Linux reads the APIC between writes to avoid this, as per
 *      the documentation. Make sure you preserve this as it affects
 *      the C stepping chips too.
 *  12AP.   not affected - worked around in hardware
 *  13AP.   not affected - worked around in hardware
 *  14AP.   we always deassert INIT during bootup
 *  15AP.   not affected - worked around in hardware
 *  16AP.   not affected - worked around in hardware
 *  17AP.   not affected - worked around in hardware
 *  18AP.   not affected - worked around in hardware
 *  19AP.   not affected - worked around in BIOS
 *
 *  If this sounds worrying believe me these bugs are either ___RARE___,
 *  or are signal timing bugs worked around in hardware and there's
 *  about nothing of note with C stepping upwards.
 */

static atomic_t stopping_cpu = ATOMIC_INIT(-1);
static bool smp_no_nmi_ipi = false;

/*
 * this function sends a 'reschedule' IPI to another CPU.
 * it goes straight through and wastes no time serializing
 * anything. Worst case is that we lose a reschedule ...
 */
static void native_smp_send_reschedule(int cpu)
{
    if (unlikely(cpu_is_offline(cpu))) {
        WARN_ON(1);
        return;
    }
    apic->send_IPI_mask(cpumask_of(cpu), RESCHEDULE_VECTOR);
}

void native_send_call_func_single_ipi(int cpu)
{
    apic->send_IPI_mask(cpumask_of(cpu), CALL_FUNCTION_SINGLE_VECTOR);
}

void native_send_call_func_ipi(const struct cpumask *mask)
{
    cpumask_var_t allbutself;

    if (!alloc_cpumask_var(&allbutself, GFP_ATOMIC)) {
        apic->send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
        return;
    }

    cpumask_copy(allbutself, cpu_online_mask);
    cpumask_clear_cpu(smp_processor_id(), allbutself);

    if (cpumask_equal(mask, allbutself) &&
        cpumask_equal(cpu_online_mask, cpu_callout_mask))
        apic->send_IPI_allbutself(CALL_FUNCTION_VECTOR);
    else
        apic->send_IPI_mask(mask, CALL_FUNCTION_VECTOR);

    free_cpumask_var(allbutself);
}

static int smp_stop_nmi_callback(unsigned int val, struct pt_regs *regs)
{
    /* We are registered on stopping cpu too, avoid spurious NMI */
    if (raw_smp_processor_id() == atomic_read(&stopping_cpu))
        return NMI_HANDLED;

    stop_this_cpu(NULL);

    return NMI_HANDLED;
}

/*
 * this function calls the 'stop' function on all other CPUs in the system.
 */

asmlinkage void smp_reboot_interrupt(void)
{
    ack_APIC_irq();
    irq_enter();
    stop_this_cpu(NULL);
    irq_exit();
}

static void native_stop_other_cpus(int wait)
{
    unsigned long flags;
    unsigned long timeout;

    if (reboot_force)
        return;

    /*
     * Use an own vector here because smp_call_function
     * does lots of things not suitable in a panic situation.
     */

    /*
     * We start by using the REBOOT_VECTOR irq.
     * The irq is treated as a sync point to allow critical
     * regions of code on other cpus to release their spin locks
     * and re-enable irqs.  Jumping straight to an NMI might
     * accidentally cause deadlocks with further shutdown/panic
     * code.  By syncing, we give the cpus up to one second to
     * finish their work before we force them off with the NMI.
     */
    if (num_online_cpus() > 1) {
        /* did someone beat us here? */
        if (atomic_cmpxchg(&stopping_cpu, -1, safe_smp_processor_id()) != -1)
            return;

        /* sync above data before sending IRQ */
        wmb();

        apic->send_IPI_allbutself(REBOOT_VECTOR);

        /*
         * Don't wait longer than a second if the caller
         * didn't ask us to wait.
         */
        timeout = USEC_PER_SEC;
        while (num_online_cpus() > 1 && (wait || timeout--))
            udelay(1);
    }
    
    /* if the REBOOT_VECTOR didn't work, try with the NMI */
    if ((num_online_cpus() > 1) && (!smp_no_nmi_ipi))  {
        if (register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback,
                     NMI_FLAG_FIRST, "smp_stop"))
            /* Note: we ignore failures here */
            /* Hope the REBOOT_IRQ is good enough */
            goto finish;

        /* sync above data before sending IRQ */
        wmb();

        pr_emerg("Shutting down cpus with NMI\n");

        apic->send_IPI_allbutself(NMI_VECTOR);

        /*
         * Don't wait longer than a 10 ms if the caller
         * didn't ask us to wait.
         */
        timeout = USEC_PER_MSEC * 10;
        while (num_online_cpus() > 1 && (wait || timeout--))
            udelay(1);
    }

finish:
    local_irq_save(flags);
    disable_local_APIC();
    local_irq_restore(flags);
}

/*
 * Reschedule call back.
 */
void smp_reschedule_interrupt(struct pt_regs *regs)
{
    ack_APIC_irq();
    inc_irq_stat(irq_resched_count);
    scheduler_ipi();
    /*
     * KVM uses this interrupt to force a cpu out of guest mode
     */
}

void smp_call_function_interrupt(struct pt_regs *regs)
{
    ack_APIC_irq();
    irq_enter();
    generic_smp_call_function_interrupt();
    inc_irq_stat(irq_call_count);
    irq_exit();
}

void smp_call_function_single_interrupt(struct pt_regs *regs)
{
    ack_APIC_irq();
    irq_enter();
    generic_smp_call_function_single_interrupt();
    inc_irq_stat(irq_call_count);
    irq_exit();
}

static int __init nonmi_ipi_setup(char *str)
{
    smp_no_nmi_ipi = true;
    return 1;
}

__setup("nonmi_ipi", nonmi_ipi_setup);

struct smp_ops smp_ops = {
    .smp_prepare_boot_cpu   = native_smp_prepare_boot_cpu,
    .smp_prepare_cpus   = native_smp_prepare_cpus,
    .smp_cpus_done      = native_smp_cpus_done,

    .stop_other_cpus    = native_stop_other_cpus,
    .smp_send_reschedule    = native_smp_send_reschedule,

    .cpu_up         = native_cpu_up,
    .cpu_die        = native_cpu_die,
    .cpu_disable        = native_cpu_disable,
    .play_dead      = native_play_dead,

    .send_call_func_ipi = native_send_call_func_ipi,
    .send_call_func_single_ipi = native_send_call_func_single_ipi,
};
EXPORT_SYMBOL_GPL(smp_ops);