FreeBSD/Linux Kernel Cross Reference
sys/i386/i386/mp_machdep.c

     /*-
      * Copyright (c) 1996, by Steve Passe
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice, this list of conditions and the following disclaimer.
     * 2. The name of the developer may NOT be used to endorse or promote products
     *    derived from this software without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/5.3/sys/i386/i386/mp_machdep.c 146167 2005-05-13 00:02:47Z nectar $");
    
    #include "opt_apic.h"
    #include "opt_cpu.h"
    #include "opt_kstack_pages.h"
    #include "opt_mp_watchdog.h"
    
    #if !defined(lint)
    #if !defined(SMP)
    #error How did you get here?
    #endif
    
    #if defined(I386_CPU) && !defined(COMPILING_LINT)
    #error SMP not supported with I386_CPU
    #endif
    #ifndef DEV_APIC
    #error The apic device is required for SMP, add "device apic" to your config file.
    #endif
    #if defined(CPU_DISABLE_CMPXCHG) && !defined(COMPILING_LINT)
    #error SMP not supported with CPU_DISABLE_CMPXCHG
    #endif
    #endif /* not lint */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/bus.h>
    #include <sys/cons.h>   /* cngetc() */
    #ifdef GPROF 
    #include <sys/gmon.h>
    #endif
    #include <sys/kernel.h>
    #include <sys/ktr.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/memrange.h>
    #include <sys/mutex.h>
    #include <sys/pcpu.h>
    #include <sys/proc.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/pmap.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_extern.h>
    
    #include <machine/apicreg.h>
    #include <machine/clock.h>
    #include <machine/md_var.h>
    #include <machine/mp_watchdog.h>
    #include <machine/pcb.h>
    #include <machine/smp.h>
    #include <machine/smptests.h>   /** COUNT_XINVLTLB_HITS */
    #include <machine/specialreg.h>
    #include <machine/privatespace.h>
    
    #define WARMBOOT_TARGET         0
    #define WARMBOOT_OFF            (KERNBASE + 0x0467)
    #define WARMBOOT_SEG            (KERNBASE + 0x0469)
    
    #define CMOS_REG                (0x70)
    #define CMOS_DATA               (0x71)
    #define BIOS_RESET              (0x0f)
    #define BIOS_WARM               (0x0a)
    
    /*
     * this code MUST be enabled here and in mpboot.s.
     * it follows the very early stages of AP boot by placing values in CMOS ram.
     * it NORMALLY will never be needed and thus the primitive method for enabling.
     *
    #define CHECK_POINTS
     */
   
   #if defined(CHECK_POINTS) && !defined(PC98)
   #define CHECK_READ(A)    (outb(CMOS_REG, (A)), inb(CMOS_DATA))
   #define CHECK_WRITE(A,D) (outb(CMOS_REG, (A)), outb(CMOS_DATA, (D)))
   
   #define CHECK_INIT(D);                          \
           CHECK_WRITE(0x34, (D));                 \
           CHECK_WRITE(0x35, (D));                 \
           CHECK_WRITE(0x36, (D));                 \
           CHECK_WRITE(0x37, (D));                 \
           CHECK_WRITE(0x38, (D));                 \
           CHECK_WRITE(0x39, (D));
   
   #define CHECK_PRINT(S);                         \
           printf("%s: %d, %d, %d, %d, %d, %d\n",  \
              (S),                                 \
              CHECK_READ(0x34),                    \
              CHECK_READ(0x35),                    \
              CHECK_READ(0x36),                    \
              CHECK_READ(0x37),                    \
              CHECK_READ(0x38),                    \
              CHECK_READ(0x39));
   
   #else                           /* CHECK_POINTS */
   
   #define CHECK_INIT(D)
   #define CHECK_PRINT(S)
   #define CHECK_WRITE(A, D)
   
   #endif                          /* CHECK_POINTS */
   
   /*
    * Values to send to the POST hardware.
    */
   #define MP_BOOTADDRESS_POST     0x10
   #define MP_PROBE_POST           0x11
   #define MPTABLE_PASS1_POST      0x12
   
   #define MP_START_POST           0x13
   #define MP_ENABLE_POST          0x14
   #define MPTABLE_PASS2_POST      0x15
   
   #define START_ALL_APS_POST      0x16
   #define INSTALL_AP_TRAMP_POST   0x17
   #define START_AP_POST           0x18
   
   #define MP_ANNOUNCE_POST        0x19
   
   /* lock region used by kernel profiling */
   int     mcount_lock;
   
   /** XXX FIXME: where does this really belong, isa.h/isa.c perhaps? */
   int     current_postcode;
   
   int     mp_naps;                /* # of Applications processors */
   int     boot_cpu_id = -1;       /* designated BSP */
   extern  int nkpt;
   
   /*
    * CPU topology map datastructures for HTT.
    */
   static struct cpu_group mp_groups[MAXCPU];
   static struct cpu_top mp_top;
   
   /* AP uses this during bootstrap.  Do not staticize.  */
   char *bootSTK;
   static int bootAP;
   
   /* Hotwire a 0->4MB V==P mapping */
   extern pt_entry_t *KPTphys;
   
   /* SMP page table page */
   extern pt_entry_t *SMPpt;
   
   struct pcb stoppcbs[MAXCPU];
   
   /* Variables needed for SMP tlb shootdown. */
   vm_offset_t smp_tlb_addr1;
   vm_offset_t smp_tlb_addr2;
   volatile int smp_tlb_wait;
   
   /*
    * Local data and functions.
    */
   
   static u_int logical_cpus;
   
   /* used to hold the AP's until we are ready to release them */
   static struct mtx ap_boot_mtx;
   
   /* Set to 1 once we're ready to let the APs out of the pen. */
   static volatile int aps_ready = 0;
   
   /*
    * Store data from cpu_add() until later in the boot when we actually setup
    * the APs.
    */
   struct cpu_info {
           int     cpu_present:1;
           int     cpu_bsp:1;
   } static cpu_info[MAXCPU];
   static int cpu_apic_ids[MAXCPU];
   
   /* Holds pending bitmap based IPIs per CPU */
   static volatile u_int cpu_ipi_pending[MAXCPU];
   
   static u_int boot_address;
   
   static void     set_logical_apic_ids(void);
   static int      start_all_aps(void);
   static void     install_ap_tramp(void);
   static int      start_ap(int apic_id);
   static void     release_aps(void *dummy);
   
   static int      hlt_logical_cpus;
   static u_int    hyperthreading_cpus;
   static cpumask_t        hyperthreading_cpus_mask;
   static int      hyperthreading_allowed;
   static struct   sysctl_ctx_list logical_cpu_clist;
   
   static void
   mem_range_AP_init(void)
   {
           if (mem_range_softc.mr_op && mem_range_softc.mr_op->initAP)
                   mem_range_softc.mr_op->initAP(&mem_range_softc);
   }
   
   void
   mp_topology(void)
   {
           struct cpu_group *group;
           int logical_cpus;
           int apic_id;
           int groups;
           int cpu;
   
           /* Build the smp_topology map. */
           /* Nothing to do if there is no HTT support. */
           if ((cpu_feature & CPUID_HTT) == 0)
                   return;
           logical_cpus = (cpu_procinfo & CPUID_HTT_CORES) >> 16;
           if (logical_cpus <= 1)
                   return;
           group = &mp_groups[0];
           groups = 1;
           for (cpu = 0, apic_id = 0; apic_id < MAXCPU; apic_id++) {
                   if (!cpu_info[apic_id].cpu_present)
                           continue;
                   /*
                    * If the current group has members and we're not a logical
                    * cpu, create a new group.
                    */
                   if (group->cg_count != 0 && (apic_id % logical_cpus) == 0) {
                           group++;
                           groups++;
                   }
                   group->cg_count++;
                   group->cg_mask |= 1 << cpu;
                   cpu++;
           }
   
           mp_top.ct_count = groups;
           mp_top.ct_group = mp_groups;
           smp_topology = &mp_top;
   }
   
   
   /*
    * Calculate usable address in base memory for AP trampoline code.
    */
   u_int
   mp_bootaddress(u_int basemem)
   {
           POSTCODE(MP_BOOTADDRESS_POST);
   
           boot_address = trunc_page(basemem);     /* round down to 4k boundary */
           if ((basemem - boot_address) < bootMP_size)
                   boot_address -= PAGE_SIZE;      /* not enough, lower by 4k */
   
           return boot_address;
   }
   
   void
   cpu_add(u_int apic_id, char boot_cpu)
   {
   
           if (apic_id >= MAXCPU) {
                   printf("SMP: CPU %d exceeds maximum CPU %d, ignoring\n",
                       apic_id, MAXCPU - 1);
                   return;
           }
           KASSERT(cpu_info[apic_id].cpu_present == 0, ("CPU %d added twice",
               apic_id));
           cpu_info[apic_id].cpu_present = 1;
           if (boot_cpu) {
                   KASSERT(boot_cpu_id == -1,
                       ("CPU %d claims to be BSP, but CPU %d already is", apic_id,
                       boot_cpu_id));
                   boot_cpu_id = apic_id;
                   cpu_info[apic_id].cpu_bsp = 1;
           }
           mp_ncpus++;
           if (bootverbose)
                   printf("SMP: Added CPU %d (%s)\n", apic_id, boot_cpu ? "BSP" :
                       "AP");
           
   }
   
   void
   cpu_mp_setmaxid(void)
   {
   
           mp_maxid = MAXCPU - 1;
   }
   
   int
   cpu_mp_probe(void)
   {
   
           /*
            * Always record BSP in CPU map so that the mbuf init code works
            * correctly.
            */
           all_cpus = 1;
           if (mp_ncpus == 0) {
                   /*
                    * No CPUs were found, so this must be a UP system.  Setup
                    * the variables to represent a system with a single CPU
                    * with an id of 0.
                    */
                   mp_ncpus = 1;
                   return (0);
           }
   
           /* At least one CPU was found. */
           if (mp_ncpus == 1) {
                   /*
                    * One CPU was found, so this must be a UP system with
                    * an I/O APIC.
                    */
                   return (0);
           }
   
           /* At least two CPUs were found. */
           return (1);
   }
   
   /*
    * Initialize the IPI handlers and start up the AP's.
    */
   void
   cpu_mp_start(void)
   {
           int i;
           u_int threads_per_cache, p[4];
   
           POSTCODE(MP_START_POST);
   
           /* Initialize the logical ID to APIC ID table. */
           for (i = 0; i < MAXCPU; i++) {
                   cpu_apic_ids[i] = -1;
                   cpu_ipi_pending[i] = 0;
           }
   
           /* Install an inter-CPU IPI for TLB invalidation */
           setidt(IPI_INVLTLB, IDTVEC(invltlb),
                  SDT_SYS386IGT, SEL_KPL, GSEL(GCODE_SEL, SEL_KPL));
           setidt(IPI_INVLPG, IDTVEC(invlpg),
                  SDT_SYS386IGT, SEL_KPL, GSEL(GCODE_SEL, SEL_KPL));
           setidt(IPI_INVLRNG, IDTVEC(invlrng),
                  SDT_SYS386IGT, SEL_KPL, GSEL(GCODE_SEL, SEL_KPL));
           
           /* Install an inter-CPU IPI for lazy pmap release */
           setidt(IPI_LAZYPMAP, IDTVEC(lazypmap),
                  SDT_SYS386IGT, SEL_KPL, GSEL(GCODE_SEL, SEL_KPL));
   
           /* Install an inter-CPU IPI for all-CPU rendezvous */
           setidt(IPI_RENDEZVOUS, IDTVEC(rendezvous),
                  SDT_SYS386IGT, SEL_KPL, GSEL(GCODE_SEL, SEL_KPL));
   
           /* Install generic inter-CPU IPI handler */
           setidt(IPI_BITMAP_VECTOR, IDTVEC(ipi_intr_bitmap_handler),
                  SDT_SYS386IGT, SEL_KPL, GSEL(GCODE_SEL, SEL_KPL));
   
           /* Install an inter-CPU IPI for CPU stop/restart */
           setidt(IPI_STOP, IDTVEC(cpustop),
                  SDT_SYS386IGT, SEL_KPL, GSEL(GCODE_SEL, SEL_KPL));
   
   
           /* Set boot_cpu_id if needed. */
           if (boot_cpu_id == -1) {
                   boot_cpu_id = PCPU_GET(apic_id);
                   cpu_info[boot_cpu_id].cpu_bsp = 1;
           } else
                   KASSERT(boot_cpu_id == PCPU_GET(apic_id),
                       ("BSP's APIC ID doesn't match boot_cpu_id"));
           cpu_apic_ids[0] = boot_cpu_id;
   
           /* Start each Application Processor */
           start_all_aps();
   
           /* Setup the initial logical CPUs info. */
           logical_cpus = logical_cpus_mask = 0;
           if (cpu_feature & CPUID_HTT)
                   logical_cpus = (cpu_procinfo & CPUID_HTT_CORES) >> 16;
   
           /*
            * Work out if hyperthreading is *really* enabled.  This
            * is made really ugly by the fact that processors lie: Dual
            * core processors claim to be hyperthreaded even when they're
            * not, presumably because they want to be treated the same
            * way as HTT with respect to per-cpu software licensing.
            * At the time of writing (May 12, 2005) the only hyperthreaded
            * cpus are from Intel, and Intel's dual-core processors can be
            * identified via the "deterministic cache parameters" cpuid
            * calls.
            */
           /*
            * First determine if this is an Intel processor which claims
            * to have hyperthreading support.
            */
           if ((cpu_feature & CPUID_HTT) &&
               (strcmp(cpu_vendor, "GenuineIntel") == 0)) {
                   /*
                    * If the "deterministic cache parameters" cpuid calls
                    * are available, use them.
                    */
                   if (cpu_high >= 4) {
                           /* Ask the processor about up to 32 caches. */
                           for (i = 0; i < 32; i++) {
                                   cpuid_count(4, i, p);
                                   threads_per_cache = ((p[0] & 0x3ffc000) >> 14) + 1;
                                   if (hyperthreading_cpus < threads_per_cache)
                                           hyperthreading_cpus = threads_per_cache;
                                   if ((p[0] & 0x1f) == 0)
                                           break;
                           }
                   }
   
                   /*
                    * If the deterministic cache parameters are not
                    * available, or if no caches were reported to exist,
                    * just accept what the HTT flag indicated.
                    */
                   if (hyperthreading_cpus == 0)
                           hyperthreading_cpus = logical_cpus;
           }
   
           set_logical_apic_ids();
   }
   
   
   /*
    * Print various information about the SMP system hardware and setup.
    */
   void
   cpu_mp_announce(void)
   {
           int i, x;
   
           POSTCODE(MP_ANNOUNCE_POST);
   
           /* List CPUs */
           printf(" cpu0 (BSP): APIC ID: %2d\n", boot_cpu_id);
           for (i = 1, x = 0; x < MAXCPU; x++) {
                   if (cpu_info[x].cpu_present && !cpu_info[x].cpu_bsp) {
                           KASSERT(i < mp_ncpus,
                               ("mp_ncpus and actual cpus are out of whack"));
                           printf(" cpu%d (AP): APIC ID: %2d\n", i++, x);
                   }
           }
   }
   
   /*
    * AP CPU's call this to initialize themselves.
    */
   void
   init_secondary(void)
   {
           int     gsel_tss;
           int     x, myid;
           u_int   cr0;
   
           /* bootAP is set in start_ap() to our ID. */
           myid = bootAP;
           gdt_segs[GPRIV_SEL].ssd_base = (int) &SMP_prvspace[myid];
           gdt_segs[GPROC0_SEL].ssd_base =
                   (int) &SMP_prvspace[myid].pcpu.pc_common_tss;
           SMP_prvspace[myid].pcpu.pc_prvspace =
                   &SMP_prvspace[myid].pcpu;
   
           for (x = 0; x < NGDT; x++) {
                   ssdtosd(&gdt_segs[x], &gdt[myid * NGDT + x].sd);
           }
   
           r_gdt.rd_limit = NGDT * sizeof(gdt[0]) - 1;
           r_gdt.rd_base = (int) &gdt[myid * NGDT];
           lgdt(&r_gdt);                   /* does magic intra-segment return */
   
           lidt(&r_idt);
   
           lldt(_default_ldt);
           PCPU_SET(currentldt, _default_ldt);
   
           gsel_tss = GSEL(GPROC0_SEL, SEL_KPL);
           gdt[myid * NGDT + GPROC0_SEL].sd.sd_type = SDT_SYS386TSS;
           PCPU_SET(common_tss.tss_esp0, 0); /* not used until after switch */
           PCPU_SET(common_tss.tss_ss0, GSEL(GDATA_SEL, SEL_KPL));
           PCPU_SET(common_tss.tss_ioopt, (sizeof (struct i386tss)) << 16);
           PCPU_SET(tss_gdt, &gdt[myid * NGDT + GPROC0_SEL].sd);
           PCPU_SET(common_tssd, *PCPU_GET(tss_gdt));
           ltr(gsel_tss);
   
           /*
            * Set to a known state:
            * Set by mpboot.s: CR0_PG, CR0_PE
            * Set by cpu_setregs: CR0_NE, CR0_MP, CR0_TS, CR0_WP, CR0_AM
            */
           cr0 = rcr0();
           cr0 &= ~(CR0_CD | CR0_NW | CR0_EM);
           load_cr0(cr0);
           CHECK_WRITE(0x38, 5);
           
           /* Disable local APIC just to be sure. */
           lapic_disable();
   
           /* signal our startup to the BSP. */
           mp_naps++;
           CHECK_WRITE(0x39, 6);
   
           /* Spin until the BSP releases the AP's. */
           while (!aps_ready)
                   ia32_pause();
   
           /* BSP may have changed PTD while we were waiting */
           invltlb();
           pmap_invalidate_range(kernel_pmap, 0, NKPT * NBPDR - 1);
   
   #if defined(I586_CPU) && !defined(NO_F00F_HACK)
           lidt(&r_idt);
   #endif
   
           /* set up CPU registers and state */
           cpu_setregs();
   
           /* set up FPU state on the AP */
           npxinit(__INITIAL_NPXCW__);
   
           /* set up SSE registers */
           enable_sse();
   
           /* A quick check from sanity claus */
           if (PCPU_GET(apic_id) != lapic_id()) {
                   printf("SMP: cpuid = %d\n", PCPU_GET(cpuid));
                   printf("SMP: actual apic_id = %d\n", lapic_id());
                   printf("SMP: correct apic_id = %d\n", PCPU_GET(apic_id));
                   printf("PTD[MPPTDI] = %#jx\n", (uintmax_t)PTD[MPPTDI]);
                   panic("cpuid mismatch! boom!!");
           }
   
           mtx_lock_spin(&ap_boot_mtx);
   
           /* Init local apic for irq's */
           lapic_setup();
   
           /* Set memory range attributes for this CPU to match the BSP */
           mem_range_AP_init();
   
           smp_cpus++;
   
           CTR1(KTR_SMP, "SMP: AP CPU #%d Launched", PCPU_GET(cpuid));
           printf("SMP: AP CPU #%d Launched!\n", PCPU_GET(cpuid));
   
           /* Determine if we are a logical CPU. */
           if (logical_cpus > 1 && PCPU_GET(apic_id) % logical_cpus != 0)
                   logical_cpus_mask |= PCPU_GET(cpumask);
           
           /* Determine if we are a hyperthread. */
           if (hyperthreading_cpus > 1 &&
               PCPU_GET(apic_id) % hyperthreading_cpus != 0)
                   hyperthreading_cpus_mask |= PCPU_GET(cpumask);
   
           /* Build our map of 'other' CPUs. */
           PCPU_SET(other_cpus, all_cpus & ~PCPU_GET(cpumask));
   
           if (bootverbose)
                   lapic_dump("AP");
   
           if (smp_cpus == mp_ncpus) {
                   /* enable IPI's, tlb shootdown, freezes etc */
                   atomic_store_rel_int(&smp_started, 1);
                   smp_active = 1;  /* historic */
           }
   
           mtx_unlock_spin(&ap_boot_mtx);
   
           /* wait until all the AP's are up */
           while (smp_started == 0)
                   ia32_pause();
   
           /* ok, now grab sched_lock and enter the scheduler */
           mtx_lock_spin(&sched_lock);
   
           binuptime(PCPU_PTR(switchtime));
           PCPU_SET(switchticks, ticks);
   
           cpu_throw(NULL, choosethread());        /* doesn't return */
   
           panic("scheduler returned us to %s", __func__);
           /* NOTREACHED */
   }
   
   /*******************************************************************
    * local functions and data
    */
   
   /*
    * Set the APIC logical IDs.
    *
    * We want to cluster logical CPU's within the same APIC ID cluster.
    * Since logical CPU's are aligned simply filling in the clusters in
    * APIC ID order works fine.  Note that this does not try to balance
    * the number of CPU's in each cluster. (XXX?)
    */
   static void
   set_logical_apic_ids(void)
   {
           u_int apic_id, cluster, cluster_id;
   
           /* Force us to allocate cluster 0 at the start. */
           cluster = -1;
           cluster_id = APIC_MAX_INTRACLUSTER_ID;
           for (apic_id = 0; apic_id < MAXCPU; apic_id++) {
                   if (!cpu_info[apic_id].cpu_present)
                           continue;
                   if (cluster_id == APIC_MAX_INTRACLUSTER_ID) {
                           cluster = ioapic_next_logical_cluster();
                           cluster_id = 0;
                   } else
                           cluster_id++;
                   if (bootverbose)
                           printf("APIC ID: physical %u, logical %u:%u\n",
                               apic_id, cluster, cluster_id);
                   lapic_set_logical_id(apic_id, cluster, cluster_id);
           }
   }
   
   /*
    * start each AP in our list
    */
   static int
   start_all_aps(void)
   {
   #ifndef PC98
           u_char mpbiosreason;
   #endif
           u_long mpbioswarmvec;
           struct pcpu *pc;
           char *stack;
           uintptr_t kptbase;
           int i, pg, apic_id, cpu;
   
           POSTCODE(START_ALL_APS_POST);
   
           mtx_init(&ap_boot_mtx, "ap boot", NULL, MTX_SPIN);
   
           /* install the AP 1st level boot code */
           install_ap_tramp();
   
           /* save the current value of the warm-start vector */
           mpbioswarmvec = *((u_long *) WARMBOOT_OFF);
   #ifndef PC98
           outb(CMOS_REG, BIOS_RESET);
           mpbiosreason = inb(CMOS_DATA);
   #endif
   
           /* set up temporary P==V mapping for AP boot */
           /* XXX this is a hack, we should boot the AP on its own stack/PTD */
           kptbase = (uintptr_t)(void *)KPTphys;
           for (i = 0; i < NKPT; i++)
                   PTD[i] = (pd_entry_t)(PG_V | PG_RW |
                       ((kptbase + i * PAGE_SIZE) & PG_FRAME));
           invltlb();
   
           /* start each AP */
           for (cpu = 0, apic_id = 0; apic_id < MAXCPU; apic_id++) {
                   if (!cpu_info[apic_id].cpu_present ||
                       cpu_info[apic_id].cpu_bsp)
                           continue;
                   cpu++;
   
                   /* save APIC ID for this logical ID */
                   cpu_apic_ids[cpu] = apic_id;
   
                   /* first page of AP's private space */
                   pg = cpu * i386_btop(sizeof(struct privatespace));
   
                   /* allocate a new private data page */
                   pc = (struct pcpu *)kmem_alloc(kernel_map, PAGE_SIZE);
   
                   /* wire it into the private page table page */
                   SMPpt[pg] = (pt_entry_t)(PG_V | PG_RW | vtophys(pc));
   
                   /* allocate and set up an idle stack data page */
                   stack = (char *)kmem_alloc(kernel_map, KSTACK_PAGES * PAGE_SIZE); /* XXXKSE */
                   for (i = 0; i < KSTACK_PAGES; i++)
                           SMPpt[pg + 1 + i] = (pt_entry_t)
                               (PG_V | PG_RW | vtophys(PAGE_SIZE * i + stack));
   
                   /* prime data page for it to use */
                   pcpu_init(pc, cpu, sizeof(struct pcpu));
                   pc->pc_apic_id = apic_id;
   
                   /* setup a vector to our boot code */
                   *((volatile u_short *) WARMBOOT_OFF) = WARMBOOT_TARGET;
                   *((volatile u_short *) WARMBOOT_SEG) = (boot_address >> 4);
   #ifndef PC98
                   outb(CMOS_REG, BIOS_RESET);
                   outb(CMOS_DATA, BIOS_WARM);     /* 'warm-start' */
   #endif
   
                   bootSTK = &SMP_prvspace[cpu].idlekstack[KSTACK_PAGES *
                       PAGE_SIZE];
                   bootAP = cpu;
   
                   /* attempt to start the Application Processor */
                   CHECK_INIT(99); /* setup checkpoints */
                   if (!start_ap(apic_id)) {
                           printf("AP #%d (PHY# %d) failed!\n", cpu, apic_id);
                           CHECK_PRINT("trace");   /* show checkpoints */
                           /* better panic as the AP may be running loose */
                           printf("panic y/n? [y] ");
                           if (cngetc() != 'n')
                                   panic("bye-bye");
                   }
                   CHECK_PRINT("trace");           /* show checkpoints */
   
                   all_cpus |= (1 << cpu);         /* record AP in CPU map */
           }
   
           /* build our map of 'other' CPUs */
           PCPU_SET(other_cpus, all_cpus & ~PCPU_GET(cpumask));
   
           /* restore the warmstart vector */
           *(u_long *) WARMBOOT_OFF = mpbioswarmvec;
   #ifndef PC98
           outb(CMOS_REG, BIOS_RESET);
           outb(CMOS_DATA, mpbiosreason);
   #endif
   
           /*
            * Set up the idle context for the BSP.  Similar to above except
            * that some was done by locore, some by pmap.c and some is implicit
            * because the BSP is cpu#0 and the page is initially zero and also
            * because we can refer to variables by name on the BSP..
            */
   
           /* Allocate and setup BSP idle stack */
           stack = (char *)kmem_alloc(kernel_map, KSTACK_PAGES * PAGE_SIZE);
           for (i = 0; i < KSTACK_PAGES; i++)
                   SMPpt[1 + i] = (pt_entry_t)
                       (PG_V | PG_RW | vtophys(PAGE_SIZE * i + stack));
   
           for (i = 0; i < NKPT; i++)
                   PTD[i] = 0;
           pmap_invalidate_range(kernel_pmap, 0, NKPT * NBPDR - 1);
   
           /* number of APs actually started */
           return mp_naps;
   }
   
   /*
    * load the 1st level AP boot code into base memory.
    */
   
   /* targets for relocation */
   extern void bigJump(void);
   extern void bootCodeSeg(void);
   extern void bootDataSeg(void);
   extern void MPentry(void);
   extern u_int MP_GDT;
   extern u_int mp_gdtbase;
   
   static void
   install_ap_tramp(void)
   {
           int     x;
           int     size = *(int *) ((u_long) & bootMP_size);
           vm_offset_t va = boot_address + KERNBASE;
           u_char *src = (u_char *) ((u_long) bootMP);
           u_char *dst = (u_char *) va;
           u_int   boot_base = (u_int) bootMP;
           u_int8_t *dst8;
           u_int16_t *dst16;
           u_int32_t *dst32;
   
           POSTCODE(INSTALL_AP_TRAMP_POST);
   
           KASSERT (size <= PAGE_SIZE,
               ("'size' do not fit into PAGE_SIZE, as expected."));
           pmap_kenter(va, boot_address);
           pmap_invalidate_page (kernel_pmap, va);
           for (x = 0; x < size; ++x)
                   *dst++ = *src++;
   
           /*
            * modify addresses in code we just moved to basemem. unfortunately we
            * need fairly detailed info about mpboot.s for this to work.  changes
            * to mpboot.s might require changes here.
            */
   
           /* boot code is located in KERNEL space */
           dst = (u_char *) va;
   
           /* modify the lgdt arg */
           dst32 = (u_int32_t *) (dst + ((u_int) & mp_gdtbase - boot_base));
           *dst32 = boot_address + ((u_int) & MP_GDT - boot_base);
   
           /* modify the ljmp target for MPentry() */
           dst32 = (u_int32_t *) (dst + ((u_int) bigJump - boot_base) + 1);
           *dst32 = ((u_int) MPentry - KERNBASE);
   
           /* modify the target for boot code segment */
           dst16 = (u_int16_t *) (dst + ((u_int) bootCodeSeg - boot_base));
           dst8 = (u_int8_t *) (dst16 + 1);
           *dst16 = (u_int) boot_address & 0xffff;
           *dst8 = ((u_int) boot_address >> 16) & 0xff;
   
           /* modify the target for boot data segment */
           dst16 = (u_int16_t *) (dst + ((u_int) bootDataSeg - boot_base));
           dst8 = (u_int8_t *) (dst16 + 1);
           *dst16 = (u_int) boot_address & 0xffff;
           *dst8 = ((u_int) boot_address >> 16) & 0xff;
   }
   
   /*
    * This function starts the AP (application processor) identified
    * by the APIC ID 'physicalCpu'.  It does quite a "song and dance"
    * to accomplish this.  This is necessary because of the nuances
    * of the different hardware we might encounter.  It isn't pretty,
    * but it seems to work.
    */
   static int
   start_ap(int apic_id)
   {
           int vector, ms;
           int cpus;
   
           POSTCODE(START_AP_POST);
   
           /* calculate the vector */
           vector = (boot_address >> 12) & 0xff;
   
           /* used as a watchpoint to signal AP startup */
           cpus = mp_naps;
   
           /*
            * first we do an INIT/RESET IPI this INIT IPI might be run, reseting
            * and running the target CPU. OR this INIT IPI might be latched (P5
            * bug), CPU waiting for STARTUP IPI. OR this INIT IPI might be
            * ignored.
            */
   
           /* do an INIT IPI: assert RESET */
           lapic_ipi_raw(APIC_DEST_DESTFLD | APIC_TRIGMOD_EDGE |
               APIC_LEVEL_ASSERT | APIC_DESTMODE_PHY | APIC_DELMODE_INIT, apic_id);
   
           /* wait for pending status end */
           lapic_ipi_wait(-1);
   
           /* do an INIT IPI: deassert RESET */
           lapic_ipi_raw(APIC_DEST_ALLESELF | APIC_TRIGMOD_LEVEL |
               APIC_LEVEL_DEASSERT | APIC_DESTMODE_PHY | APIC_DELMODE_INIT, 0);
   
           /* wait for pending status end */
           DELAY(10000);           /* wait ~10mS */
           lapic_ipi_wait(-1);
   
           /*
            * next we do a STARTUP IPI: the previous INIT IPI might still be
            * latched, (P5 bug) this 1st STARTUP would then terminate
            * immediately, and the previously started INIT IPI would continue. OR
            * the previous INIT IPI has already run. and this STARTUP IPI will
            * run. OR the previous INIT IPI was ignored. and this STARTUP IPI
            * will run.
            */
   
           /* do a STARTUP IPI */
           lapic_ipi_raw(APIC_DEST_DESTFLD | APIC_TRIGMOD_EDGE |
               APIC_LEVEL_DEASSERT | APIC_DESTMODE_PHY | APIC_DELMODE_STARTUP |
               vector, apic_id);
           lapic_ipi_wait(-1);
           DELAY(200);             /* wait ~200uS */
   
           /*
            * finally we do a 2nd STARTUP IPI: this 2nd STARTUP IPI should run IF
            * the previous STARTUP IPI was cancelled by a latched INIT IPI. OR
            * this STARTUP IPI will be ignored, as only ONE STARTUP IPI is
            * recognized after hardware RESET or INIT IPI.
            */
   
           lapic_ipi_raw(APIC_DEST_DESTFLD | APIC_TRIGMOD_EDGE |
               APIC_LEVEL_DEASSERT | APIC_DESTMODE_PHY | APIC_DELMODE_STARTUP |
               vector, apic_id);
           lapic_ipi_wait(-1);
           DELAY(200);             /* wait ~200uS */
   
           /* Wait up to 5 seconds for it to start. */
           for (ms = 0; ms < 5000; ms++) {
                   if (mp_naps > cpus)
                           return 1;       /* return SUCCESS */
                   DELAY(1000);
           }
           return 0;               /* return FAILURE */
   }
   
   #ifdef COUNT_XINVLTLB_HITS
   u_int xhits_gbl[MAXCPU];
   u_int xhits_pg[MAXCPU];
   u_int xhits_rng[MAXCPU];
   SYSCTL_NODE(_debug, OID_AUTO, xhits, CTLFLAG_RW, 0, "");
   SYSCTL_OPAQUE(_debug_xhits, OID_AUTO, global, CTLFLAG_RW, &xhits_gbl,
       sizeof(xhits_gbl), "IU", "");
   SYSCTL_OPAQUE(_debug_xhits, OID_AUTO, page, CTLFLAG_RW, &xhits_pg,
       sizeof(xhits_pg), "IU", "");
   SYSCTL_OPAQUE(_debug_xhits, OID_AUTO, range, CTLFLAG_RW, &xhits_rng,
       sizeof(xhits_rng), "IU", "");
   
   u_int ipi_global;
   u_int ipi_page;
   u_int ipi_range;
   u_int ipi_range_size;
   SYSCTL_INT(_debug_xhits, OID_AUTO, ipi_global, CTLFLAG_RW, &ipi_global, 0, "");
   SYSCTL_INT(_debug_xhits, OID_AUTO, ipi_page, CTLFLAG_RW, &ipi_page, 0, "");
   SYSCTL_INT(_debug_xhits, OID_AUTO, ipi_range, CTLFLAG_RW, &ipi_range, 0, "");
   SYSCTL_INT(_debug_xhits, OID_AUTO, ipi_range_size, CTLFLAG_RW, &ipi_range_size,
       0, "");
   
   u_int ipi_masked_global;
   u_int ipi_masked_page;
   u_int ipi_masked_range;
   u_int ipi_masked_range_size;
   SYSCTL_INT(_debug_xhits, OID_AUTO, ipi_masked_global, CTLFLAG_RW,
       &ipi_masked_global, 0, "");
   SYSCTL_INT(_debug_xhits, OID_AUTO, ipi_masked_page, CTLFLAG_RW,
       &ipi_masked_page, 0, "");
   SYSCTL_INT(_debug_xhits, OID_AUTO, ipi_masked_range, CTLFLAG_RW,
       &ipi_masked_range, 0, "");
   SYSCTL_INT(_debug_xhits, OID_AUTO, ipi_masked_range_size, CTLFLAG_RW,
       &ipi_masked_range_size, 0, "");
   #endif /* COUNT_XINVLTLB_HITS */
   
   /*
    * Flush the TLB on all other CPU's
    */
   static void
   smp_tlb_shootdown(u_int vector, vm_offset_t addr1, vm_offset_t addr2)
   {
           u_int ncpu;
   
           ncpu = mp_ncpus - 1;    /* does not shootdown self */
           if (ncpu < 1)
                   return;         /* no other cpus */
           mtx_assert(&smp_rv_mtx, MA_OWNED);
           smp_tlb_addr1 = addr1;
           smp_tlb_addr2 = addr2;
           atomic_store_rel_int(&smp_tlb_wait, 0);
           ipi_all_but_self(vector);
           while (smp_tlb_wait < ncpu)
                   ia32_pause();
   }
   
   /*
    * This is about as magic as it gets.  fortune(1) has got similar code
    * for reversing bits in a word.  Who thinks up this stuff??
    *
    * Yes, it does appear to be consistently faster than:
    * while (i = ffs(m)) {
    *      m >>= i;
    *      bits++;
    * }
    * and
    * while (lsb = (m & -m)) {     // This is magic too
    *      m &= ~lsb;              // or: m ^= lsb
    *      bits++;
    * }
    * Both of these latter forms do some very strange things on gcc-3.1 with
    * -mcpu=pentiumpro and/or -march=pentiumpro and/or -O or -O2.
    * There is probably an SSE or MMX popcnt instruction.
    *
    * I wonder if this should be in libkern?
    *
    * XXX Stop the presses!  Another one:
    * static __inline u_int32_t
    * popcnt1(u_int32_t v)
    * {
    *      v -= ((v >> 1) & 0x55555555);
    *      v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
    *      v = (v + (v >> 4)) & 0x0F0F0F0F;
    *      return (v * 0x01010101) >> 24;
   * }
   * The downside is that it has a multiply.  With a pentium3 with
   * -mcpu=pentiumpro and -march=pentiumpro then gcc-3.1 will use
   * an imull, and in that case it is faster.  In most other cases
   * it appears slightly slower.
   *
   * Another variant (also from fortune):
   * #define BITCOUNT(x) (((BX_(x)+(BX_(x)>>4)) & 0x0F0F0F0F) % 255)
   * #define  BX_(x)     ((x) - (((x)>>1)&0x77777777)            \
   *                          - (((x)>>2)&0x33333333)            \
   *                          - (((x)>>3)&0x11111111))
   */
  static __inline u_int32_t
  popcnt(u_int32_t m)
  {
  
          m = (m & 0x55555555) + ((m & 0xaaaaaaaa) >> 1);
          m = (m & 0x33333333) + ((m & 0xcccccccc) >> 2);
          m = (m & 0x0f0f0f0f) + ((m & 0xf0f0f0f0) >> 4);
          m = (m & 0x00ff00ff) + ((m & 0xff00ff00) >> 8);
          m = (m & 0x0000ffff) + ((m & 0xffff0000) >> 16);
          return m;
  }
  
  static void
  smp_targeted_tlb_shootdown(u_int mask, u_int vector, vm_offset_t addr1, vm_offset_t addr2)
  {
          int ncpu, othercpus;
  
          othercpus = mp_ncpus - 1;
          if (mask == (u_int)-1) {
                  ncpu = othercpus;
                  if (ncpu < 1)
                          return;
          } else {
                  mask &= ~PCPU_GET(cpumask);
                  if (mask == 0)
                          return;
                  ncpu = popcnt(mask);
                  if (ncpu > othercpus) {
                          /* XXX this should be a panic offence */
                          printf("SMP: tlb shootdown to %d other cpus (only have %d)\n",
                              ncpu, othercpus);
                          ncpu = othercpus;
                  }
                  /* XXX should be a panic, implied by mask == 0 above */
                  if (ncpu < 1)
                          return;
          }
          mtx_assert(&smp_rv_mtx, MA_OWNED);
          smp_tlb_addr1 = addr1;
          smp_tlb_addr2 = addr2;
          atomic_store_rel_int(&smp_tlb_wait, 0);
          if (mask == (u_int)-1)
                  ipi_all_but_self(vector);
          else
                  ipi_selected(mask, vector);
          while (smp_tlb_wait < ncpu)
                  ia32_pause();
  }
  
  void
  smp_invltlb(void)
  {
          if (smp_started) {
                  smp_tlb_shootdown(IPI_INVLTLB, 0, 0);
  #ifdef COUNT_XINVLTLB_HITS
                  ipi_global++;
  #endif
          }
  }
  
  void
  smp_invlpg(vm_offset_t addr)
  {
          if (smp_started) {
                  smp_tlb_shootdown(IPI_INVLPG, addr, 0);
  #ifdef COUNT_XINVLTLB_HITS
                  ipi_page++;
  #endif
          }
  }
  
  void
  smp_invlpg_range(vm_offset_t addr1, vm_offset_t addr2)
  {
          if (smp_started) {
                  smp_tlb_shootdown(IPI_INVLRNG, addr1, addr2);
  #ifdef COUNT_XINVLTLB_HITS
                  ipi_range++;
                  ipi_range_size += (addr2 - addr1) / PAGE_SIZE;
  #endif
          }
  }
  
  void
  smp_masked_invltlb(u_int mask)
  {
          if (smp_started) {
                  smp_targeted_tlb_shootdown(mask, IPI_INVLTLB, 0, 0);
  #ifdef COUNT_XINVLTLB_HITS
                  ipi_masked_global++;
  #endif
          }
  }
  
  void
  smp_masked_invlpg(u_int mask, vm_offset_t addr)
  {
          if (smp_started) {
                  smp_targeted_tlb_shootdown(mask, IPI_INVLPG, addr, 0);
  #ifdef COUNT_XINVLTLB_HITS
                  ipi_masked_page++;
  #endif
          }
  }
  
  void
  smp_masked_invlpg_range(u_int mask, vm_offset_t addr1, vm_offset_t addr2)
  {
          if (smp_started) {
                  smp_targeted_tlb_shootdown(mask, IPI_INVLRNG, addr1, addr2);
  #ifdef COUNT_XINVLTLB_HITS
                  ipi_masked_range++;
                  ipi_masked_range_size += (addr2 - addr1) / PAGE_SIZE;
  #endif
          }
  }
  
  
  /*
   * For statclock, we send an IPI to all CPU's to have them call this
   * function.
   */
  
  void
  forward_statclock(void)
  {
          int map;
  
          CTR0(KTR_SMP, "forward_statclock");
  
          if (!smp_started || cold || panicstr)
                  return;
  
          map = PCPU_GET(other_cpus) & ~(stopped_cpus|hlt_cpus_mask);
          if (map != 0)
                  ipi_selected(map, IPI_STATCLOCK);
  }
  
  /*
   * For each hardclock(), we send an IPI to all other CPU's to have them
   * execute this function.  It would be nice to reduce contention on
   * sched_lock if we could simply peek at the CPU to determine the user/kernel
   * state and call hardclock_process() on the CPU receiving the clock interrupt
   * and then just use a simple IPI to handle any ast's if needed.
   */
  
  void 
  forward_hardclock(void)
  {
          u_int map;
  
          CTR0(KTR_SMP, "forward_hardclock");
  
          if (!smp_started || cold || panicstr)
                  return;
  
          map = PCPU_GET(other_cpus) & ~(stopped_cpus|hlt_cpus_mask);
          if (map != 0)
                  ipi_selected(map, IPI_HARDCLOCK);
  }
  
  void
  ipi_bitmap_handler(struct clockframe frame)
  {
          int cpu = PCPU_GET(cpuid);
          u_int ipi_bitmap;
          struct thread *td;
  
          ipi_bitmap = atomic_readandclear_int(&cpu_ipi_pending[cpu]);
  
          critical_enter();
  
          /* Nothing to do for AST */
  
          if (ipi_bitmap & (1 << IPI_HARDCLOCK)) {
                  td = curthread; 
                  td->td_intr_nesting_level++;
                  hardclock_process(&frame);
                  td->td_intr_nesting_level--;    
          }
  
          if (ipi_bitmap & (1 << IPI_STATCLOCK)) {
                  CTR0(KTR_SMP, "forwarded_statclock");
  
                  td = curthread;
                  td->td_intr_nesting_level++;
                  if (profprocs != 0)
                          profclock(&frame);
                  if (pscnt == psdiv)
                          statclock(&frame);
                  td->td_intr_nesting_level--;
          }
  
          critical_exit();
  }
  
  /*
   * send an IPI to a set of cpus.
   */
  void
  ipi_selected(u_int32_t cpus, u_int ipi)
  {
          int cpu;
          u_int bitmap = 0;
          u_int old_pending;
          u_int new_pending;
  
          if (IPI_IS_BITMAPED(ipi)) { 
                  bitmap = 1 << ipi;
                  ipi = IPI_BITMAP_VECTOR;
          }
  
          CTR3(KTR_SMP, "%s: cpus: %x ipi: %x", __func__, cpus, ipi);
          while ((cpu = ffs(cpus)) != 0) {
                  cpu--;
                  cpus &= ~(1 << cpu);
  
                  KASSERT(cpu_apic_ids[cpu] != -1,
                      ("IPI to non-existent CPU %d", cpu));
  
                  if (bitmap) {
                          do {
                                  old_pending = cpu_ipi_pending[cpu];
                                  new_pending = old_pending | bitmap;
                          } while  (!atomic_cmpset_int(&cpu_ipi_pending[cpu],old_pending, new_pending));  
  
                          if (old_pending)
                                  continue;
                  }
  
                  lapic_ipi_vectored(ipi, cpu_apic_ids[cpu]);
          }
  
  }
  
  /*
   * send an IPI INTerrupt containing 'vector' to all CPUs, including myself
   */
  void
  ipi_all(u_int ipi)
  {
  
          CTR2(KTR_SMP, "%s: ipi: %x", __func__, ipi);
          lapic_ipi_vectored(ipi, APIC_IPI_DEST_ALL);
  }
  
  /*
   * send an IPI to all CPUs EXCEPT myself
   */
  void
  ipi_all_but_self(u_int ipi)
  {
  
          CTR2(KTR_SMP, "%s: ipi: %x", __func__, ipi);
          lapic_ipi_vectored(ipi, APIC_IPI_DEST_OTHERS);
  }
  
  /*
   * send an IPI to myself
   */
  void
  ipi_self(u_int ipi)
  {
  
          CTR2(KTR_SMP, "%s: ipi: %x", __func__, ipi);
          lapic_ipi_vectored(ipi, APIC_IPI_DEST_SELF);
  }
  
  /*
   * This is called once the rest of the system is up and running and we're
   * ready to let the AP's out of the pen.
   */
  static void
  release_aps(void *dummy __unused)
  {
  
          if (mp_ncpus == 1) 
                  return;
          mtx_lock_spin(&sched_lock);
          atomic_store_rel_int(&aps_ready, 1);
          while (smp_started == 0)
                  ia32_pause();
          mtx_unlock_spin(&sched_lock);
  }
  SYSINIT(start_aps, SI_SUB_SMP, SI_ORDER_FIRST, release_aps, NULL);
  
  static int
  sysctl_hlt_cpus(SYSCTL_HANDLER_ARGS)
  {
          u_int mask;
          int error;
  
          mask = hlt_cpus_mask;
          error = sysctl_handle_int(oidp, &mask, 0, req);
          if (error || !req->newptr)
                  return (error);
  
          if (logical_cpus_mask != 0 &&
              (mask & logical_cpus_mask) == logical_cpus_mask)
                  hlt_logical_cpus = 1;
          else
                  hlt_logical_cpus = 0;
  
          if (! hyperthreading_allowed)
                  mask |= hyperthreading_cpus_mask;
  
          if ((mask & all_cpus) == all_cpus)
                  mask &= ~(1<<0);
          hlt_cpus_mask = mask;
          return (error);
  }
  SYSCTL_PROC(_machdep, OID_AUTO, hlt_cpus, CTLTYPE_INT|CTLFLAG_RW,
      0, 0, sysctl_hlt_cpus, "IU",
      "Bitmap of CPUs to halt.  101 (binary) will halt CPUs 0 and 2.");
  
  static int
  sysctl_hlt_logical_cpus(SYSCTL_HANDLER_ARGS)
  {
          int disable, error;
  
          disable = hlt_logical_cpus;
          error = sysctl_handle_int(oidp, &disable, 0, req);
          if (error || !req->newptr)
                  return (error);
  
          if (disable)
                  hlt_cpus_mask |= logical_cpus_mask;
          else
                  hlt_cpus_mask &= ~logical_cpus_mask;
  
          if (! hyperthreading_allowed)
                  hlt_cpus_mask |= hyperthreading_cpus_mask;
  
          if ((hlt_cpus_mask & all_cpus) == all_cpus)
                  hlt_cpus_mask &= ~(1<<0);
  
          hlt_logical_cpus = disable;
          return (error);
  }
  
  static int
  sysctl_hyperthreading_allowed(SYSCTL_HANDLER_ARGS)
  {
          int allowed, error;
  
          allowed = hyperthreading_allowed;
          error = sysctl_handle_int(oidp, &allowed, 0, req);
          if (error || !req->newptr)
                  return (error);
  
          if (allowed)
                  hlt_cpus_mask &= ~hyperthreading_cpus_mask;
          else
                  hlt_cpus_mask |= hyperthreading_cpus_mask;
  
          if (logical_cpus_mask != 0 &&
              (hlt_cpus_mask & logical_cpus_mask) == logical_cpus_mask)
                  hlt_logical_cpus = 1;
          else
                  hlt_logical_cpus = 0;
  
          if ((hlt_cpus_mask & all_cpus) == all_cpus)
                  hlt_cpus_mask &= ~(1<<0);
  
          hyperthreading_allowed = allowed;
          return (error);
  }
  
  static void
  cpu_hlt_setup(void *dummy __unused)
  {
  
          if (logical_cpus_mask != 0) {
                  TUNABLE_INT_FETCH("machdep.hlt_logical_cpus",
                      &hlt_logical_cpus);
                  sysctl_ctx_init(&logical_cpu_clist);
                  SYSCTL_ADD_PROC(&logical_cpu_clist,
                      SYSCTL_STATIC_CHILDREN(_machdep), OID_AUTO,
                      "hlt_logical_cpus", CTLTYPE_INT|CTLFLAG_RW, 0, 0,
                      sysctl_hlt_logical_cpus, "IU", "");
                  SYSCTL_ADD_UINT(&logical_cpu_clist,
                      SYSCTL_STATIC_CHILDREN(_machdep), OID_AUTO,
                      "logical_cpus_mask", CTLTYPE_INT|CTLFLAG_RD,
                      &logical_cpus_mask, 0, "");
  
                  if (hlt_logical_cpus)
                          hlt_cpus_mask |= logical_cpus_mask;
  
                  /*
                   * If necessary for security purposes, force
                   * hyperthreading off, regardless of the value
                   * of hlt_logical_cpus.
                   */
                  if (hyperthreading_cpus_mask) {
                          TUNABLE_INT_FETCH("machdep.hyperthreading_allowed",
                              &hyperthreading_allowed);
                          SYSCTL_ADD_PROC(&logical_cpu_clist,
                              SYSCTL_STATIC_CHILDREN(_machdep), OID_AUTO,
                              "hyperthreading_allowed", CTLTYPE_INT|CTLFLAG_RW,
                              0, 0, sysctl_hyperthreading_allowed, "IU", "");
                          if (! hyperthreading_allowed)
                                  hlt_cpus_mask |= hyperthreading_cpus_mask;
                  }
          }
  }
  SYSINIT(cpu_hlt, SI_SUB_SMP, SI_ORDER_ANY, cpu_hlt_setup, NULL);
  
  int
  mp_grab_cpu_hlt(void)
  {
          u_int mask = PCPU_GET(cpumask);
  #ifdef MP_WATCHDOG
          u_int cpuid = PCPU_GET(cpuid);
  #endif
          int retval;
  
  #ifdef MP_WATCHDOG
          ap_watchdog(cpuid);
  #endif
  
          retval = mask & hlt_cpus_mask;
          while (mask & hlt_cpus_mask)
                  __asm __volatile("sti; hlt" : : : "memory");
          return (retval);
  }

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