FreeBSD/Linux Kernel Cross Reference
sys/amd64/amd64/vm_machdep.c

     /*-
      * Copyright (c) 1982, 1986 The Regents of the University of California.
      * Copyright (c) 1989, 1990 William Jolitz
      * Copyright (c) 1994 John Dyson
      * All rights reserved.
      *
      * This code is derived from software contributed to Berkeley by
      * the Systems Programming Group of the University of Utah Computer
      * Science Department, and William Jolitz.
     *
     * 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. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the University of
     *      California, Berkeley and its contributors.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
     *
     *      from: @(#)vm_machdep.c  7.3 (Berkeley) 5/13/91
     *      Utah $Hdr: vm_machdep.c 1.16.1.1 89/06/23$
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/10.0/sys/amd64/amd64/vm_machdep.c 255844 2013-09-24 12:24:48Z kib $");
    
    #include "opt_isa.h"
    #include "opt_cpu.h"
    #include "opt_compat.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/bio.h>
    #include <sys/buf.h>
    #include <sys/kernel.h>
    #include <sys/ktr.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/mbuf.h>
    #include <sys/mutex.h>
    #include <sys/pioctl.h>
    #include <sys/proc.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    #include <sys/sysent.h>
    #include <sys/unistd.h>
    #include <sys/vnode.h>
    #include <sys/vmmeter.h>
    
    #include <machine/cpu.h>
    #include <machine/md_var.h>
    #include <machine/pcb.h>
    #include <machine/smp.h>
    #include <machine/specialreg.h>
    #include <machine/tss.h>
    
    #include <vm/vm.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_page.h>
    #include <vm/vm_map.h>
    #include <vm/vm_param.h>
    
    #include <x86/isa/isa.h>
    
    static void     cpu_reset_real(void);
    #ifdef SMP
    static void     cpu_reset_proxy(void);
    static u_int    cpu_reset_proxyid;
    static volatile u_int   cpu_reset_proxy_active;
    #endif
    
    _Static_assert(OFFSETOF_CURTHREAD == offsetof(struct pcpu, pc_curthread),
        "OFFSETOF_CURTHREAD does not correspond with offset of pc_curthread.");
    _Static_assert(OFFSETOF_CURPCB == offsetof(struct pcpu, pc_curpcb),
        "OFFSETOF_CURPCB does not correspond with offset of pc_curpcb.");
    
    struct savefpu *
    get_pcb_user_save_td(struct thread *td)
    {
           vm_offset_t p;
   
           p = td->td_kstack + td->td_kstack_pages * PAGE_SIZE -
               cpu_max_ext_state_size;
           KASSERT((p % 64) == 0, ("Unaligned pcb_user_save area"));
           return ((struct savefpu *)p);
   }
   
   struct savefpu *
   get_pcb_user_save_pcb(struct pcb *pcb)
   {
           vm_offset_t p;
   
           p = (vm_offset_t)(pcb + 1);
           return ((struct savefpu *)p);
   }
   
   struct pcb *
   get_pcb_td(struct thread *td)
   {
           vm_offset_t p;
   
           p = td->td_kstack + td->td_kstack_pages * PAGE_SIZE -
               cpu_max_ext_state_size - sizeof(struct pcb);
           return ((struct pcb *)p);
   }
   
   void *
   alloc_fpusave(int flags)
   {
           struct pcb *res;
           struct savefpu_ymm *sf;
   
           res = malloc(cpu_max_ext_state_size, M_DEVBUF, flags);
           if (use_xsave) {
                   sf = (struct savefpu_ymm *)res;
                   bzero(&sf->sv_xstate.sx_hd, sizeof(sf->sv_xstate.sx_hd));
                   sf->sv_xstate.sx_hd.xstate_bv = xsave_mask;
           }
           return (res);
   }
   
   /*
    * Finish a fork operation, with process p2 nearly set up.
    * Copy and update the pcb, set up the stack so that the child
    * ready to run and return to user mode.
    */
   void
   cpu_fork(td1, p2, td2, flags)
           register struct thread *td1;
           register struct proc *p2;
           struct thread *td2;
           int flags;
   {
           register struct proc *p1;
           struct pcb *pcb2;
           struct mdproc *mdp1, *mdp2;
           struct proc_ldt *pldt;
           pmap_t pmap2;
   
           p1 = td1->td_proc;
           if ((flags & RFPROC) == 0) {
                   if ((flags & RFMEM) == 0) {
                           /* unshare user LDT */
                           mdp1 = &p1->p_md;
                           mtx_lock(&dt_lock);
                           if ((pldt = mdp1->md_ldt) != NULL &&
                               pldt->ldt_refcnt > 1 &&
                               user_ldt_alloc(p1, 1) == NULL)
                                   panic("could not copy LDT");
                           mtx_unlock(&dt_lock);
                   }
                   return;
           }
   
           /* Ensure that td1's pcb is up to date. */
           fpuexit(td1);
   
           /* Point the pcb to the top of the stack */
           pcb2 = get_pcb_td(td2);
           td2->td_pcb = pcb2;
   
           /* Copy td1's pcb */
           bcopy(td1->td_pcb, pcb2, sizeof(*pcb2));
   
           /* Properly initialize pcb_save */
           pcb2->pcb_save = get_pcb_user_save_pcb(pcb2);
           bcopy(get_pcb_user_save_td(td1), get_pcb_user_save_pcb(pcb2),
               cpu_max_ext_state_size);
   
           /* Point mdproc and then copy over td1's contents */
           mdp2 = &p2->p_md;
           bcopy(&p1->p_md, mdp2, sizeof(*mdp2));
   
           /*
            * Create a new fresh stack for the new process.
            * Copy the trap frame for the return to user mode as if from a
            * syscall.  This copies most of the user mode register values.
            */
           td2->td_frame = (struct trapframe *)td2->td_pcb - 1;
           bcopy(td1->td_frame, td2->td_frame, sizeof(struct trapframe));
   
           td2->td_frame->tf_rax = 0;              /* Child returns zero */
           td2->td_frame->tf_rflags &= ~PSL_C;     /* success */
           td2->td_frame->tf_rdx = 1;
   
           /*
            * If the parent process has the trap bit set (i.e. a debugger had
            * single stepped the process to the system call), we need to clear
            * the trap flag from the new frame unless the debugger had set PF_FORK
            * on the parent.  Otherwise, the child will receive a (likely
            * unexpected) SIGTRAP when it executes the first instruction after
            * returning  to userland.
            */
           if ((p1->p_pfsflags & PF_FORK) == 0)
                   td2->td_frame->tf_rflags &= ~PSL_T;
   
           /*
            * Set registers for trampoline to user mode.  Leave space for the
            * return address on stack.  These are the kernel mode register values.
            */
           pmap2 = vmspace_pmap(p2->p_vmspace);
           pcb2->pcb_cr3 = pmap2->pm_cr3;
           pcb2->pcb_r12 = (register_t)fork_return;        /* fork_trampoline argument */
           pcb2->pcb_rbp = 0;
           pcb2->pcb_rsp = (register_t)td2->td_frame - sizeof(void *);
           pcb2->pcb_rbx = (register_t)td2;                /* fork_trampoline argument */
           pcb2->pcb_rip = (register_t)fork_trampoline;
           /*-
            * pcb2->pcb_dr*:       cloned above.
            * pcb2->pcb_savefpu:   cloned above.
            * pcb2->pcb_flags:     cloned above.
            * pcb2->pcb_onfault:   cloned above (always NULL here?).
            * pcb2->pcb_[fg]sbase: cloned above
            */
   
           /* Setup to release spin count in fork_exit(). */
           td2->td_md.md_spinlock_count = 1;
           td2->td_md.md_saved_flags = PSL_KERNEL | PSL_I;
   
           /* As an i386, do not copy io permission bitmap. */
           pcb2->pcb_tssp = NULL;
   
           /* New segment registers. */
           set_pcb_flags(pcb2, PCB_FULL_IRET);
   
           /* Copy the LDT, if necessary. */
           mdp1 = &td1->td_proc->p_md;
           mdp2 = &p2->p_md;
           mtx_lock(&dt_lock);
           if (mdp1->md_ldt != NULL) {
                   if (flags & RFMEM) {
                           mdp1->md_ldt->ldt_refcnt++;
                           mdp2->md_ldt = mdp1->md_ldt;
                           bcopy(&mdp1->md_ldt_sd, &mdp2->md_ldt_sd, sizeof(struct
                               system_segment_descriptor));
                   } else {
                           mdp2->md_ldt = NULL;
                           mdp2->md_ldt = user_ldt_alloc(p2, 0);
                           if (mdp2->md_ldt == NULL)
                                   panic("could not copy LDT");
                           amd64_set_ldt_data(td2, 0, max_ldt_segment,
                               (struct user_segment_descriptor *)
                               mdp1->md_ldt->ldt_base);
                   }
           } else
                   mdp2->md_ldt = NULL;
           mtx_unlock(&dt_lock);
   
           /*
            * Now, cpu_switch() can schedule the new process.
            * pcb_rsp is loaded pointing to the cpu_switch() stack frame
            * containing the return address when exiting cpu_switch.
            * This will normally be to fork_trampoline(), which will have
            * %ebx loaded with the new proc's pointer.  fork_trampoline()
            * will set up a stack to call fork_return(p, frame); to complete
            * the return to user-mode.
            */
   }
   
   /*
    * Intercept the return address from a freshly forked process that has NOT
    * been scheduled yet.
    *
    * This is needed to make kernel threads stay in kernel mode.
    */
   void
   cpu_set_fork_handler(td, func, arg)
           struct thread *td;
           void (*func)(void *);
           void *arg;
   {
           /*
            * Note that the trap frame follows the args, so the function
            * is really called like this:  func(arg, frame);
            */
           td->td_pcb->pcb_r12 = (long) func;      /* function */
           td->td_pcb->pcb_rbx = (long) arg;       /* first arg */
   }
   
   void
   cpu_exit(struct thread *td)
   {
   
           /*
            * If this process has a custom LDT, release it.
            */
           mtx_lock(&dt_lock);
           if (td->td_proc->p_md.md_ldt != 0)
                   user_ldt_free(td);
           else
                   mtx_unlock(&dt_lock);
   }
   
   void
   cpu_thread_exit(struct thread *td)
   {
           struct pcb *pcb;
   
           critical_enter();
           if (td == PCPU_GET(fpcurthread))
                   fpudrop();
           critical_exit();
   
           pcb = td->td_pcb;
   
           /* Disable any hardware breakpoints. */
           if (pcb->pcb_flags & PCB_DBREGS) {
                   reset_dbregs();
                   clear_pcb_flags(pcb, PCB_DBREGS);
           }
   }
   
   void
   cpu_thread_clean(struct thread *td)
   {
           struct pcb *pcb;
   
           pcb = td->td_pcb;
   
           /*
            * Clean TSS/iomap
            */
           if (pcb->pcb_tssp != NULL) {
                   kmem_free(kernel_arena, (vm_offset_t)pcb->pcb_tssp,
                       ctob(IOPAGES + 1));
                   pcb->pcb_tssp = NULL;
           }
   }
   
   void
   cpu_thread_swapin(struct thread *td)
   {
   }
   
   void
   cpu_thread_swapout(struct thread *td)
   {
   }
   
   void
   cpu_thread_alloc(struct thread *td)
   {
           struct pcb *pcb;
           struct xstate_hdr *xhdr;
   
           td->td_pcb = pcb = get_pcb_td(td);
           td->td_frame = (struct trapframe *)pcb - 1;
           pcb->pcb_save = get_pcb_user_save_pcb(pcb);
           if (use_xsave) {
                   xhdr = (struct xstate_hdr *)(pcb->pcb_save + 1);
                   bzero(xhdr, sizeof(*xhdr));
                   xhdr->xstate_bv = xsave_mask;
           }
   }
   
   void
   cpu_thread_free(struct thread *td)
   {
   
           cpu_thread_clean(td);
   }
   
   void
   cpu_set_syscall_retval(struct thread *td, int error)
   {
   
           switch (error) {
           case 0:
                   td->td_frame->tf_rax = td->td_retval[0];
                   td->td_frame->tf_rdx = td->td_retval[1];
                   td->td_frame->tf_rflags &= ~PSL_C;
                   break;
   
           case ERESTART:
                   /*
                    * Reconstruct pc, we know that 'syscall' is 2 bytes,
                    * lcall $X,y is 7 bytes, int 0x80 is 2 bytes.
                    * We saved this in tf_err.
                    * %r10 (which was holding the value of %rcx) is restored
                    * for the next iteration.
                    * %r10 restore is only required for freebsd/amd64 processes,
                    * but shall be innocent for any ia32 ABI.
                    *
                    * Require full context restore to get the arguments
                    * in the registers reloaded at return to usermode.
                    */
                   td->td_frame->tf_rip -= td->td_frame->tf_err;
                   td->td_frame->tf_r10 = td->td_frame->tf_rcx;
                   set_pcb_flags(td->td_pcb, PCB_FULL_IRET);
                   break;
   
           case EJUSTRETURN:
                   break;
   
           default:
                   if (td->td_proc->p_sysent->sv_errsize) {
                           if (error >= td->td_proc->p_sysent->sv_errsize)
                                   error = -1;     /* XXX */
                           else
                                   error = td->td_proc->p_sysent->sv_errtbl[error];
                   }
                   td->td_frame->tf_rax = error;
                   td->td_frame->tf_rflags |= PSL_C;
                   break;
           }
   }
   
   /*
    * Initialize machine state (pcb and trap frame) for a new thread about to
    * upcall. Put enough state in the new thread's PCB to get it to go back 
    * userret(), where we can intercept it again to set the return (upcall)
    * Address and stack, along with those from upcals that are from other sources
    * such as those generated in thread_userret() itself.
    */
   void
   cpu_set_upcall(struct thread *td, struct thread *td0)
   {
           struct pcb *pcb2;
   
           /* Point the pcb to the top of the stack. */
           pcb2 = td->td_pcb;
   
           /*
            * Copy the upcall pcb.  This loads kernel regs.
            * Those not loaded individually below get their default
            * values here.
            */
           bcopy(td0->td_pcb, pcb2, sizeof(*pcb2));
           clear_pcb_flags(pcb2, PCB_FPUINITDONE | PCB_USERFPUINITDONE);
           pcb2->pcb_save = get_pcb_user_save_pcb(pcb2);
           bcopy(get_pcb_user_save_td(td0), pcb2->pcb_save,
               cpu_max_ext_state_size);
           set_pcb_flags(pcb2, PCB_FULL_IRET);
   
           /*
            * Create a new fresh stack for the new thread.
            */
           bcopy(td0->td_frame, td->td_frame, sizeof(struct trapframe));
   
           /* If the current thread has the trap bit set (i.e. a debugger had
            * single stepped the process to the system call), we need to clear
            * the trap flag from the new frame. Otherwise, the new thread will
            * receive a (likely unexpected) SIGTRAP when it executes the first
            * instruction after returning to userland.
            */
           td->td_frame->tf_rflags &= ~PSL_T;
   
           /*
            * Set registers for trampoline to user mode.  Leave space for the
            * return address on stack.  These are the kernel mode register values.
            */
           pcb2->pcb_r12 = (register_t)fork_return;            /* trampoline arg */
           pcb2->pcb_rbp = 0;
           pcb2->pcb_rsp = (register_t)td->td_frame - sizeof(void *);      /* trampoline arg */
           pcb2->pcb_rbx = (register_t)td;                     /* trampoline arg */
           pcb2->pcb_rip = (register_t)fork_trampoline;
           /*
            * If we didn't copy the pcb, we'd need to do the following registers:
            * pcb2->pcb_cr3:       cloned above.
            * pcb2->pcb_dr*:       cloned above.
            * pcb2->pcb_savefpu:   cloned above.
            * pcb2->pcb_onfault:   cloned above (always NULL here?).
            * pcb2->pcb_[fg]sbase: cloned above
            */
   
           /* Setup to release spin count in fork_exit(). */
           td->td_md.md_spinlock_count = 1;
           td->td_md.md_saved_flags = PSL_KERNEL | PSL_I;
   }
   
   /*
    * Set that machine state for performing an upcall that has to
    * be done in thread_userret() so that those upcalls generated
    * in thread_userret() itself can be done as well.
    */
   void
   cpu_set_upcall_kse(struct thread *td, void (*entry)(void *), void *arg,
           stack_t *stack)
   {
   
           /* 
            * Do any extra cleaning that needs to be done.
            * The thread may have optional components
            * that are not present in a fresh thread.
            * This may be a recycled thread so make it look
            * as though it's newly allocated.
            */
           cpu_thread_clean(td);
   
   #ifdef COMPAT_FREEBSD32
           if (SV_PROC_FLAG(td->td_proc, SV_ILP32)) {
                   /*
                    * Set the trap frame to point at the beginning of the uts
                    * function.
                    */
                   td->td_frame->tf_rbp = 0;
                   td->td_frame->tf_rsp =
                      (((uintptr_t)stack->ss_sp + stack->ss_size - 4) & ~0x0f) - 4;
                   td->td_frame->tf_rip = (uintptr_t)entry;
   
                   /*
                    * Pass the address of the mailbox for this kse to the uts
                    * function as a parameter on the stack.
                    */
                   suword32((void *)(td->td_frame->tf_rsp + sizeof(int32_t)),
                       (uint32_t)(uintptr_t)arg);
   
                   return;
           }
   #endif
   
           /*
            * Set the trap frame to point at the beginning of the uts
            * function.
            */
           td->td_frame->tf_rbp = 0;
           td->td_frame->tf_rsp =
               ((register_t)stack->ss_sp + stack->ss_size) & ~0x0f;
           td->td_frame->tf_rsp -= 8;
           td->td_frame->tf_rip = (register_t)entry;
           td->td_frame->tf_ds = _udatasel;
           td->td_frame->tf_es = _udatasel;
           td->td_frame->tf_fs = _ufssel;
           td->td_frame->tf_gs = _ugssel;
           td->td_frame->tf_flags = TF_HASSEGS;
   
           /*
            * Pass the address of the mailbox for this kse to the uts
            * function as a parameter on the stack.
            */
           td->td_frame->tf_rdi = (register_t)arg;
   }
   
   int
   cpu_set_user_tls(struct thread *td, void *tls_base)
   {
           struct pcb *pcb;
   
           if ((u_int64_t)tls_base >= VM_MAXUSER_ADDRESS)
                   return (EINVAL);
   
           pcb = td->td_pcb;
           set_pcb_flags(pcb, PCB_FULL_IRET);
   #ifdef COMPAT_FREEBSD32
           if (SV_PROC_FLAG(td->td_proc, SV_ILP32)) {
                   pcb->pcb_gsbase = (register_t)tls_base;
                   return (0);
           }
   #endif
           pcb->pcb_fsbase = (register_t)tls_base;
           return (0);
   }
   
   #ifdef SMP
   static void
   cpu_reset_proxy()
   {
           cpuset_t tcrp;
   
           cpu_reset_proxy_active = 1;
           while (cpu_reset_proxy_active == 1)
                   ia32_pause(); /* Wait for other cpu to see that we've started */
   
           CPU_SETOF(cpu_reset_proxyid, &tcrp);
           stop_cpus(tcrp);
           printf("cpu_reset_proxy: Stopped CPU %d\n", cpu_reset_proxyid);
           DELAY(1000000);
           cpu_reset_real();
   }
   #endif
   
   void
   cpu_reset()
   {
   #ifdef SMP
           cpuset_t map;
           u_int cnt;
   
           if (smp_active) {
                   map = all_cpus;
                   CPU_CLR(PCPU_GET(cpuid), &map);
                   CPU_NAND(&map, &stopped_cpus);
                   if (!CPU_EMPTY(&map)) {
                           printf("cpu_reset: Stopping other CPUs\n");
                           stop_cpus(map);
                   }
   
                   if (PCPU_GET(cpuid) != 0) {
                           cpu_reset_proxyid = PCPU_GET(cpuid);
                           cpustop_restartfunc = cpu_reset_proxy;
                           cpu_reset_proxy_active = 0;
                           printf("cpu_reset: Restarting BSP\n");
   
                           /* Restart CPU #0. */
                           CPU_SETOF(0, &started_cpus);
                           wmb();
   
                           cnt = 0;
                           while (cpu_reset_proxy_active == 0 && cnt < 10000000) {
                                   ia32_pause();
                                   cnt++;  /* Wait for BSP to announce restart */
                           }
                           if (cpu_reset_proxy_active == 0)
                                   printf("cpu_reset: Failed to restart BSP\n");
                           enable_intr();
                           cpu_reset_proxy_active = 2;
   
                           while (1)
                                   ia32_pause();
                           /* NOTREACHED */
                   }
   
                   DELAY(1000000);
           }
   #endif
           cpu_reset_real();
           /* NOTREACHED */
   }
   
   static void
   cpu_reset_real()
   {
           struct region_descriptor null_idt;
           int b;
   
           disable_intr();
   
           /*
            * Attempt to do a CPU reset via the keyboard controller,
            * do not turn off GateA20, as any machine that fails
            * to do the reset here would then end up in no man's land.
            */
           outb(IO_KBD + 4, 0xFE);
           DELAY(500000);  /* wait 0.5 sec to see if that did it */
   
           /*
            * Attempt to force a reset via the Reset Control register at
            * I/O port 0xcf9.  Bit 2 forces a system reset when it
            * transitions from 0 to 1.  Bit 1 selects the type of reset
            * to attempt: 0 selects a "soft" reset, and 1 selects a
            * "hard" reset.  We try a "hard" reset.  The first write sets
            * bit 1 to select a "hard" reset and clears bit 2.  The
            * second write forces a 0 -> 1 transition in bit 2 to trigger
            * a reset.
            */
           outb(0xcf9, 0x2);
           outb(0xcf9, 0x6);
           DELAY(500000);  /* wait 0.5 sec to see if that did it */
   
           /*
            * Attempt to force a reset via the Fast A20 and Init register
            * at I/O port 0x92.  Bit 1 serves as an alternate A20 gate.
            * Bit 0 asserts INIT# when set to 1.  We are careful to only
            * preserve bit 1 while setting bit 0.  We also must clear bit
            * 0 before setting it if it isn't already clear.
            */
           b = inb(0x92);
           if (b != 0xff) {
                   if ((b & 0x1) != 0)
                           outb(0x92, b & 0xfe);
                   outb(0x92, b | 0x1);
                   DELAY(500000);  /* wait 0.5 sec to see if that did it */
           }
   
           printf("No known reset method worked, attempting CPU shutdown\n");
           DELAY(1000000); /* wait 1 sec for printf to complete */
   
           /* Wipe the IDT. */
           null_idt.rd_limit = 0;
           null_idt.rd_base = 0;
           lidt(&null_idt);
   
           /* "good night, sweet prince .... <THUNK!>" */
           breakpoint();
   
           /* NOTREACHED */
           while(1);
   }
   
   /*
    * Software interrupt handler for queued VM system processing.
    */   
   void  
   swi_vm(void *dummy) 
   {     
           if (busdma_swi_pending != 0)
                   busdma_swi();
   }
   
   /*
    * Tell whether this address is in some physical memory region.
    * Currently used by the kernel coredump code in order to avoid
    * dumping the ``ISA memory hole'' which could cause indefinite hangs,
    * or other unpredictable behaviour.
    */
   
   int
   is_physical_memory(vm_paddr_t addr)
   {
   
   #ifdef DEV_ISA
           /* The ISA ``memory hole''. */
           if (addr >= 0xa0000 && addr < 0x100000)
                   return 0;
   #endif
   
           /*
            * stuff other tests for known memory-mapped devices (PCI?)
            * here
            */
   
           return 1;
   }

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