FreeBSD/Linux Kernel Cross Reference
sys/i386/i386/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/5.4/sys/i386/i386/vm_machdep.c 145335 2005-04-20 19:11:07Z cvs2svn $");
    
    #include "opt_isa.h"
    #include "opt_npx.h"
    #ifdef PC98
    #include "opt_pc98.h"
    #endif
    #include "opt_reset.h"
    #include "opt_cpu.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/bio.h>
    #include <sys/buf.h>
    #include <sys/kse.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/sf_buf.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    #include <sys/unistd.h>
    #include <sys/vnode.h>
    #include <sys/vmmeter.h>
    
    #include <machine/cpu.h>
    #include <machine/cputypes.h>
    #include <machine/md_var.h>
    #include <machine/pcb.h>
    #include <machine/pcb_ext.h>
    #include <machine/smp.h>
    #include <machine/vm86.h>
    
    #ifdef CPU_ELAN
    #include <machine/elan_mmcr.h>
    #endif
    
    #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>
    
    #ifdef PC98
    #include <pc98/pc98/pc98.h>
    #else
    #include <i386/isa/isa.h>
    #endif
    
    #ifndef NSFBUFS
   #define NSFBUFS         (512 + maxusers * 16)
   #endif
   
   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 void     sf_buf_init(void *arg);
   SYSINIT(sock_sf, SI_SUB_MBUF, SI_ORDER_ANY, sf_buf_init, NULL)
   
   LIST_HEAD(sf_head, sf_buf);
   
   /*
    * A hash table of active sendfile(2) buffers
    */
   static struct sf_head *sf_buf_active;
   static u_long sf_buf_hashmask;
   
   #define SF_BUF_HASH(m)  (((m) - vm_page_array) & sf_buf_hashmask)
   
   static TAILQ_HEAD(, sf_buf) sf_buf_freelist;
   static u_int    sf_buf_alloc_want;
   
   /*
    * A lock used to synchronize access to the hash table and free list
    */
   static struct mtx sf_buf_lock;
   
   extern int      _ucodesel, _udatasel;
   
   /*
    * 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 *mdp2;
   #ifdef DEV_NPX
           register_t savecrit;
   #endif
   
           p1 = td1->td_proc;
           if ((flags & RFPROC) == 0) {
                   if ((flags & RFMEM) == 0) {
                           /* unshare user LDT */
                           struct mdproc *mdp1 = &p1->p_md;
                           struct proc_ldt *pldt = mdp1->md_ldt;
                           if (pldt && pldt->ldt_refcnt > 1) {
                                   pldt = user_ldt_alloc(mdp1, pldt->ldt_len);
                                   if (pldt == NULL)
                                           panic("could not copy LDT");
                                   mdp1->md_ldt = pldt;
                                   set_user_ldt(mdp1);
                                   user_ldt_free(td1);
                           }
                   }
                   return;
           }
   
           /* Ensure that p1's pcb is up to date. */
   #ifdef DEV_NPX
           if (td1 == curthread)
                   td1->td_pcb->pcb_gs = rgs();
           savecrit = intr_disable();
           if (PCPU_GET(fpcurthread) == td1)
                   npxsave(&td1->td_pcb->pcb_save);
           intr_restore(savecrit);
   #endif
   
           /* Point the pcb to the top of the stack */
           pcb2 = (struct pcb *)(td2->td_kstack +
               td2->td_kstack_pages * PAGE_SIZE) - 1;
           td2->td_pcb = pcb2;
   
           /* Copy p1's pcb */
           bcopy(td1->td_pcb, pcb2, sizeof(*pcb2));
   
           /* 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.
            * The -16 is so we can expand the trapframe if we go to vm86.
            */
           td2->td_frame = (struct trapframe *)((caddr_t)td2->td_pcb - 16) - 1;
           bcopy(td1->td_frame, td2->td_frame, sizeof(struct trapframe));
   
           td2->td_frame->tf_eax = 0;              /* Child returns zero */
           td2->td_frame->tf_eflags &= ~PSL_C;     /* success */
           td2->td_frame->tf_edx = 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_eflags &= ~PSL_T;
   
           /*
            * Set registers for trampoline to user mode.  Leave space for the
            * return address on stack.  These are the kernel mode register values.
            */
   #ifdef PAE
           pcb2->pcb_cr3 = vtophys(vmspace_pmap(p2->p_vmspace)->pm_pdpt);
   #else
           pcb2->pcb_cr3 = vtophys(vmspace_pmap(p2->p_vmspace)->pm_pdir);
   #endif
           pcb2->pcb_edi = 0;
           pcb2->pcb_esi = (int)fork_return;       /* fork_trampoline argument */
           pcb2->pcb_ebp = 0;
           pcb2->pcb_esp = (int)td2->td_frame - sizeof(void *);
           pcb2->pcb_ebx = (int)td2;               /* fork_trampoline argument */
           pcb2->pcb_eip = (int)fork_trampoline;
           pcb2->pcb_psl = PSL_KERNEL;             /* ints disabled */
           pcb2->pcb_gs = rgs();
           /*-
            * 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_gs:        cloned above.
            * pcb2->pcb_ext:       cleared below.
            */
   
           /*
            * XXX don't copy the i/o pages.  this should probably be fixed.
            */
           pcb2->pcb_ext = 0;
   
           /* Copy the LDT, if necessary. */
           mtx_lock_spin(&sched_lock);
           if (mdp2->md_ldt != 0) {
                   if (flags & RFMEM) {
                           mdp2->md_ldt->ldt_refcnt++;
                   } else {
                           mdp2->md_ldt = user_ldt_alloc(mdp2,
                               mdp2->md_ldt->ldt_len);
                           if (mdp2->md_ldt == NULL)
                                   panic("could not copy LDT");
                   }
           }
           mtx_unlock_spin(&sched_lock);
   
           /*
            * Now, cpu_switch() can schedule the new process.
            * pcb_esp 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_esi = (int) func;       /* function */
           td->td_pcb->pcb_ebx = (int) arg;        /* first arg */
   }
   
   void
   cpu_exit(struct thread *td)
   {
           struct mdproc *mdp;
           struct pcb *pcb = td->td_pcb; 
   
   
           /* Reset pc->pcb_gs and %gs before possibly invalidating it. */
           mdp = &td->td_proc->p_md;
           if (mdp->md_ldt) {
                   td->td_pcb->pcb_gs = _udatasel;
                   load_gs(_udatasel);
                   user_ldt_free(td);
           }
           if (pcb->pcb_flags & PCB_DBREGS) {
                   /* disable all hardware breakpoints */
                   reset_dbregs();
                   pcb->pcb_flags &= ~PCB_DBREGS;
           }
   }
   
   void
   cpu_thread_exit(struct thread *td)
   {
           struct pcb *pcb = td->td_pcb; 
   #ifdef DEV_NPX
           if (td == PCPU_GET(fpcurthread))
                   npxdrop();
   #endif
           if (pcb->pcb_flags & PCB_DBREGS) {
                   /* disable all hardware breakpoints */
                   reset_dbregs();
                   pcb->pcb_flags &= ~PCB_DBREGS;
           }
   }
   
   void
   cpu_thread_clean(struct thread *td)
   {
           struct pcb *pcb;
   
           pcb = td->td_pcb; 
           if (pcb->pcb_ext != 0) {
                   /* XXXKSE  XXXSMP  not SMP SAFE.. what locks do we have? */
                   /* if (pcb->pcb_ext->ext_refcount-- == 1) ?? */
                   /*
                    * XXX do we need to move the TSS off the allocated pages
                    * before freeing them?  (not done here)
                    */
                   kmem_free(kernel_map, (vm_offset_t)pcb->pcb_ext,
                       ctob(IOPAGES + 1));
                   pcb->pcb_ext = 0;
           }
   }
   
   void
   cpu_thread_swapin(struct thread *td)
   {
   }
   
   void
   cpu_thread_swapout(struct thread *td)
   {
   }
   
   void
   cpu_thread_setup(struct thread *td)
   {
   
           td->td_pcb = (struct pcb *)(td->td_kstack +
               td->td_kstack_pages * PAGE_SIZE) - 1;
           td->td_frame = (struct trapframe *)((caddr_t)td->td_pcb - 16) - 1;
           td->td_pcb->pcb_ext = NULL; 
   }
   
   /*
    * Initialize machine state (pcb and trap frame) for a new thread about to
    * upcall. Pu t 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.
            *
            * XXXKSE It might be a good idea to simply skip this as
            * the values of the other registers may be unimportant.
            * This would remove any requirement for knowing the KSE
            * at this time (see the matching comment below for
            * more analysis) (need a good safe default).
            */
           bcopy(td0->td_pcb, pcb2, sizeof(*pcb2));
           pcb2->pcb_flags &= ~(PCB_NPXTRAP|PCB_NPXINITDONE);
   
           /*
            * Create a new fresh stack for the new thread.
            * The -16 is so we can expand the trapframe if we go to vm86.
            * Don't forget to set this stack value into whatever supplies
            * the address for the fault handlers.
            * The contexts are filled in at the time we actually DO the
            * upcall as only then do we know which KSE we got.
            */
           bcopy(td0->td_frame, td->td_frame, sizeof(struct trapframe));
   
           /*
            * Set registers for trampoline to user mode.  Leave space for the
            * return address on stack.  These are the kernel mode register values.
            */
   #ifdef PAE
           pcb2->pcb_cr3 = vtophys(vmspace_pmap(td->td_proc->p_vmspace)->pm_pdpt);
   #else
           pcb2->pcb_cr3 = vtophys(vmspace_pmap(td->td_proc->p_vmspace)->pm_pdir);
   #endif
           pcb2->pcb_edi = 0;
           pcb2->pcb_esi = (int)fork_return;                   /* trampoline arg */
           pcb2->pcb_ebp = 0;
           pcb2->pcb_esp = (int)td->td_frame - sizeof(void *); /* trampoline arg */
           pcb2->pcb_ebx = (int)td;                            /* trampoline arg */
           pcb2->pcb_eip = (int)fork_trampoline;
           pcb2->pcb_psl &= ~(PSL_I);      /* interrupts must be disabled */
           pcb2->pcb_gs = rgs();
           /*
            * If we didn't copy the pcb, we'd need to do the following registers:
            * 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_gs:        cloned above.  XXXKSE ???
            * pcb2->pcb_ext:       cleared below.
            */
            pcb2->pcb_ext = NULL;
   }
   
   /*
    * 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, struct kse_upcall *ku)
   {
   
           /* 
            * 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);
   
           /*
            * Set the trap frame to point at the beginning of the uts
            * function.
            */
           td->td_frame->tf_ebp = 0; 
           td->td_frame->tf_esp =
               (int)ku->ku_stack.ss_sp + ku->ku_stack.ss_size - 16;
           td->td_frame->tf_eip = (int)ku->ku_func;
   
           /*
            * Pass the address of the mailbox for this kse to the uts
            * function as a parameter on the stack.
            */
           suword((void *)(td->td_frame->tf_esp + sizeof(void *)),
               (int)ku->ku_mailbox);
   }
   
   /*
    * Convert kernel VA to physical address
    */
   vm_paddr_t
   kvtop(void *addr)
   {
           vm_paddr_t pa;
   
           pa = pmap_kextract((vm_offset_t)addr);
           if (pa == 0)
                   panic("kvtop: zero page frame");
           return (pa);
   }
   
   /*
    * Force reset the processor by invalidating the entire address space!
    */
   
   #ifdef SMP
   static void
   cpu_reset_proxy()
   {
   
           cpu_reset_proxy_active = 1;
           while (cpu_reset_proxy_active == 1)
                   ;        /* Wait for other cpu to see that we've started */
           stop_cpus((1<<cpu_reset_proxyid));
           printf("cpu_reset_proxy: Stopped CPU %d\n", cpu_reset_proxyid);
           DELAY(1000000);
           cpu_reset_real();
   }
   #endif
   
   void
   cpu_reset()
   {
   #ifdef SMP
           if (smp_active == 0) {
                   cpu_reset_real();
                   /* NOTREACHED */
           } else {
   
                   u_int map;
                   int cnt;
                   printf("cpu_reset called on cpu#%d\n", PCPU_GET(cpuid));
   
                   map = PCPU_GET(other_cpus) & ~ stopped_cpus;
   
                   if (map != 0) {
                           printf("cpu_reset: Stopping other CPUs\n");
                           stop_cpus(map);         /* Stop all other CPUs */
                   }
   
                   if (PCPU_GET(cpuid) == 0) {
                           DELAY(1000000);
                           cpu_reset_real();
                           /* NOTREACHED */
                   } else {
                           /* We are not BSP (CPU #0) */
   
                           cpu_reset_proxyid = PCPU_GET(cpuid);
                           cpustop_restartfunc = cpu_reset_proxy;
                           cpu_reset_proxy_active = 0;
                           printf("cpu_reset: Restarting BSP\n");
                           started_cpus = (1<<0);          /* Restart CPU #0 */
   
                           cnt = 0;
                           while (cpu_reset_proxy_active == 0 && cnt < 10000000)
                                   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);
                           /* NOTREACHED */
                   }
           }
   #else
           cpu_reset_real();
   #endif
   }
   
   static void
   cpu_reset_real()
   {
   
   #ifdef CPU_ELAN
           if (elan_mmcr != NULL)
                   elan_mmcr->RESCFG = 1;
   #endif
   
           if (cpu == CPU_GEODE1100) {
                   /* Attempt Geode's own reset */
                   outl(0xcf8, 0x80009044ul);
                   outl(0xcfc, 0xf);
           }
   
   #ifdef PC98
           /*
            * Attempt to do a CPU reset via CPU reset port.
            */
           disable_intr();
           if ((inb(0x35) & 0xa0) != 0xa0) {
                   outb(0x37, 0x0f);               /* SHUT0 = 0. */
                   outb(0x37, 0x0b);               /* SHUT1 = 0. */
           }
           outb(0xf0, 0x00);               /* Reset. */
   #else
           /*
            * Attempt to do a CPU reset via the keyboard controller,
            * do not turn of the GateA20, as any machine that fails
            * to do the reset here would then end up in no man's land.
            */
   
   #if !defined(BROKEN_KEYBOARD_RESET)
           outb(IO_KBD + 4, 0xFE);
           DELAY(500000);  /* wait 0.5 sec to see if that did it */
           printf("Keyboard reset did not work, attempting CPU shutdown\n");
           DELAY(1000000); /* wait 1 sec for printf to complete */
   #endif
   #endif /* PC98 */
           /* force a shutdown by unmapping entire address space ! */
           bzero((caddr_t)PTD, NBPTD);
   
           /* "good night, sweet prince .... <THUNK!>" */
           invltlb();
           /* NOTREACHED */
           while(1);
   }
   
   /*
    * Allocate a pool of sf_bufs (sendfile(2) or "super-fast" if you prefer. :-))
    */
   static void
   sf_buf_init(void *arg)
   {
           struct sf_buf *sf_bufs;
           vm_offset_t sf_base;
           int i;
   
           nsfbufs = NSFBUFS;
           TUNABLE_INT_FETCH("kern.ipc.nsfbufs", &nsfbufs);
   
           sf_buf_active = hashinit(nsfbufs, M_TEMP, &sf_buf_hashmask);
           TAILQ_INIT(&sf_buf_freelist);
           sf_base = kmem_alloc_nofault(kernel_map, nsfbufs * PAGE_SIZE);
           sf_bufs = malloc(nsfbufs * sizeof(struct sf_buf), M_TEMP,
               M_NOWAIT | M_ZERO);
           for (i = 0; i < nsfbufs; i++) {
                   sf_bufs[i].kva = sf_base + i * PAGE_SIZE;
                   TAILQ_INSERT_TAIL(&sf_buf_freelist, &sf_bufs[i], free_entry);
           }
           sf_buf_alloc_want = 0;
           mtx_init(&sf_buf_lock, "sf_buf", NULL, MTX_DEF);
   }
   
   /*
    * Get an sf_buf from the freelist. Will block if none are available.
    */
   struct sf_buf *
   sf_buf_alloc(struct vm_page *m, int flags)
   {
           pt_entry_t opte, *ptep;
           struct sf_head *hash_list;
           struct sf_buf *sf;
   #ifdef SMP
           cpumask_t cpumask, other_cpus;
   #endif
           int error;
   
           KASSERT(curthread->td_pinned > 0 || (flags & SFB_CPUPRIVATE) == 0,
               ("sf_buf_alloc(SFB_CPUPRIVATE): curthread not pinned"));
           hash_list = &sf_buf_active[SF_BUF_HASH(m)];
           mtx_lock(&sf_buf_lock);
           LIST_FOREACH(sf, hash_list, list_entry) {
                   if (sf->m == m) {
                           sf->ref_count++;
                           if (sf->ref_count == 1) {
                                   TAILQ_REMOVE(&sf_buf_freelist, sf, free_entry);
                                   nsfbufsused++;
                                   nsfbufspeak = imax(nsfbufspeak, nsfbufsused);
                           }
   #ifdef SMP
                           cpumask = PCPU_GET(cpumask);
                           if ((sf->cpumask & cpumask) == 0) {
                                   sf->cpumask |= cpumask;
                                   invlpg(sf->kva);
                           }
                           if ((flags & SFB_CPUPRIVATE) == 0) {
                                   other_cpus = PCPU_GET(other_cpus) & ~sf->cpumask;
                                   if (other_cpus != 0) {
                                           sf->cpumask |= other_cpus;
                                           mtx_lock_spin(&smp_ipi_mtx);
                                           smp_masked_invlpg(other_cpus, sf->kva);
                                           mtx_unlock_spin(&smp_ipi_mtx);
                                   }
                           }
   #endif
                           goto done;
                   }
           }
           while ((sf = TAILQ_FIRST(&sf_buf_freelist)) == NULL) {
                   if (flags & SFB_NOWAIT)
                           goto done;
                   sf_buf_alloc_want++;
                   mbstat.sf_allocwait++;
                   error = msleep(&sf_buf_freelist, &sf_buf_lock,
                       (flags & SFB_CATCH) ? PCATCH | PVM : PVM, "sfbufa", 0);
                   sf_buf_alloc_want--;
   
                   /*
                    * If we got a signal, don't risk going back to sleep. 
                    */
                   if (error)
                           goto done;
           }
           TAILQ_REMOVE(&sf_buf_freelist, sf, free_entry);
           if (sf->m != NULL)
                   LIST_REMOVE(sf, list_entry);
           LIST_INSERT_HEAD(hash_list, sf, list_entry);
           sf->ref_count = 1;
           sf->m = m;
           nsfbufsused++;
           nsfbufspeak = imax(nsfbufspeak, nsfbufsused);
   
           /*
            * Update the sf_buf's virtual-to-physical mapping, flushing the
            * virtual address from the TLB only if the PTE implies that the old
            * mapping has been used.  Since the reference count for the sf_buf's
            * old mapping was zero, that mapping is not currently in use.
            * Consequently, there is no need to exchange the old and new PTEs
            * atomically, even under PAE.
            */
           ptep = vtopte(sf->kva);
           opte = *ptep;
           *ptep = VM_PAGE_TO_PHYS(m) | pgeflag | PG_RW | PG_V;
   #ifdef SMP
           if (flags & SFB_CPUPRIVATE) {
                   if ((opte & (PG_A | PG_V)) == (PG_A | PG_V)) {
                           sf->cpumask = PCPU_GET(cpumask);
                           invlpg(sf->kva);
                   } else
                           sf->cpumask = all_cpus;
                   goto done;
           } else
                   sf->cpumask = all_cpus;
   #endif
           if ((opte & (PG_A | PG_V)) == (PG_A | PG_V))
                   pmap_invalidate_page(kernel_pmap, sf->kva);
   done:
           mtx_unlock(&sf_buf_lock);
           return (sf);
   }
   
   /*
    * Remove a reference from the given sf_buf, adding it to the free
    * list when its reference count reaches zero.  A freed sf_buf still,
    * however, retains its virtual-to-physical mapping until it is
    * recycled or reactivated by sf_buf_alloc(9).
    */
   void
   sf_buf_free(struct sf_buf *sf)
   {
   
           mtx_lock(&sf_buf_lock);
           sf->ref_count--;
           if (sf->ref_count == 0) {
                   TAILQ_INSERT_TAIL(&sf_buf_freelist, sf, free_entry);
                   nsfbufsused--;
                   if (sf_buf_alloc_want > 0)
                           wakeup_one(&sf_buf_freelist);
           }
           mtx_unlock(&sf_buf_lock);
   }
   
   /*
    * 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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