kernel - Make pcb_onfault more robust.

[dragonfly.git] / sys / platform / pc32 / i386 / trap.c

/*-
 * Copyright (C) 1994, David Greenman
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * the University of Utah, 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: @(#)trap.c	7.4 (Berkeley) 5/13/91
 * $FreeBSD: src/sys/i386/i386/trap.c,v 1.147.2.11 2003/02/27 19:09:59 luoqi Exp $
 */

/*
 * 386 Trap and System call handling
 */

#include "use_isa.h"
#include "use_npx.h"

#include "opt_cpu.h"
#include "opt_ddb.h"
#include "opt_ktrace.h"
#include "opt_clock.h"
#include "opt_trap.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/pioctl.h>
#include <sys/kernel.h>
#include <sys/kerneldump.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/signal2.h>
#include <sys/syscall.h>
#include <sys/sysctl.h>
#include <sys/sysent.h>
#include <sys/uio.h>
#include <sys/vmmeter.h>
#include <sys/malloc.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif
#include <sys/ktr.h>
#include <sys/upcall.h>
#include <sys/vkernel.h>
#include <sys/sysproto.h>
#include <sys/sysunion.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <sys/lock.h>
#include <vm/pmap.h>
#include <vm/vm_kern.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>
#include <vm/vm_extern.h>

#include <machine/cpu.h>
#include <machine/md_var.h>
#include <machine/pcb.h>
#include <machine/smp.h>
#include <machine/tss.h>
#include <machine/specialreg.h>
#include <machine/globaldata.h>
#include <machine/intr_machdep.h>

#include <machine_base/isa/isa_intr.h>
#include <machine_base/apic/lapic.h>

#ifdef POWERFAIL_NMI
#include <sys/syslog.h>
#include <machine/clock.h>
#endif

#include <machine/vm86.h>

#include <ddb/ddb.h>

#include <sys/msgport2.h>
#include <sys/thread2.h>
#include <sys/mplock2.h>

#ifdef SMP

#define MAKEMPSAFE(have_mplock)			\
	if (have_mplock == 0) {			\
		get_mplock();			\
		have_mplock = 1;		\
	}

#else

#define MAKEMPSAFE(have_mplock)

#endif

int (*pmath_emulate) (struct trapframe *);

extern void trap (struct trapframe *frame);
extern void syscall2 (struct trapframe *frame);

static int trap_pfault (struct trapframe *, int, vm_offset_t);
static void trap_fatal (struct trapframe *, vm_offset_t);
void dblfault_handler (void);

extern inthand_t IDTVEC(syscall);

#define MAX_TRAP_MSG		28
static char *trap_msg[] = {
	"",					/*  0 unused */
	"privileged instruction fault",		/*  1 T_PRIVINFLT */
	"",					/*  2 unused */
	"breakpoint instruction fault",		/*  3 T_BPTFLT */
	"",					/*  4 unused */
	"",					/*  5 unused */
	"arithmetic trap",			/*  6 T_ARITHTRAP */
	"system forced exception",		/*  7 T_ASTFLT */
	"",					/*  8 unused */
	"general protection fault",		/*  9 T_PROTFLT */
	"trace trap",				/* 10 T_TRCTRAP */
	"",					/* 11 unused */
	"page fault",				/* 12 T_PAGEFLT */
	"",					/* 13 unused */
	"alignment fault",			/* 14 T_ALIGNFLT */
	"",					/* 15 unused */
	"",					/* 16 unused */
	"",					/* 17 unused */
	"integer divide fault",			/* 18 T_DIVIDE */
	"non-maskable interrupt trap",		/* 19 T_NMI */
	"overflow trap",			/* 20 T_OFLOW */
	"FPU bounds check fault",		/* 21 T_BOUND */
	"FPU device not available",		/* 22 T_DNA */
	"double fault",				/* 23 T_DOUBLEFLT */
	"FPU operand fetch fault",		/* 24 T_FPOPFLT */
	"invalid TSS fault",			/* 25 T_TSSFLT */
	"segment not present fault",		/* 26 T_SEGNPFLT */
	"stack fault",				/* 27 T_STKFLT */
	"machine check trap",			/* 28 T_MCHK */
};

#if defined(I586_CPU) && !defined(NO_F00F_HACK)
extern int has_f00f_bug;
#endif

#ifdef DDB
static int ddb_on_nmi = 1;
SYSCTL_INT(_machdep, OID_AUTO, ddb_on_nmi, CTLFLAG_RW,
	&ddb_on_nmi, 0, "Go to DDB on NMI");
#endif
static int panic_on_nmi = 1;
SYSCTL_INT(_machdep, OID_AUTO, panic_on_nmi, CTLFLAG_RW,
	&panic_on_nmi, 0, "Panic on NMI");
static int fast_release;
SYSCTL_INT(_machdep, OID_AUTO, fast_release, CTLFLAG_RW,
	&fast_release, 0, "Passive Release was optimal");
static int slow_release;
SYSCTL_INT(_machdep, OID_AUTO, slow_release, CTLFLAG_RW,
	&slow_release, 0, "Passive Release was nonoptimal");

MALLOC_DEFINE(M_SYSMSG, "sysmsg", "sysmsg structure");
extern int max_sysmsg;

/*
 * Passively intercepts the thread switch function to increase the thread
 * priority from a user priority to a kernel priority, reducing
 * syscall and trap overhead for the case where no switch occurs.
 *
 * Synchronizes td_ucred with p_ucred.  This is used by system calls,
 * signal handling, faults, AST traps, and anything else that enters the
 * kernel from userland and provides the kernel with a stable read-only
 * copy of the process ucred.
 */
static __inline void
userenter(struct thread *curtd, struct proc *curp)
{
	struct ucred *ocred;
	struct ucred *ncred;

	curtd->td_release = lwkt_passive_release;

	if (curtd->td_ucred != curp->p_ucred) {
		ncred = crhold(curp->p_ucred);
		ocred = curtd->td_ucred;
		curtd->td_ucred = ncred;
		if (ocred)
			crfree(ocred);
	}

}

/*
 * Handle signals, upcalls, profiling, and other AST's and/or tasks that
 * must be completed before we can return to or try to return to userland.
 *
 * Note that td_sticks is a 64 bit quantity, but there's no point doing 64
 * arithmatic on the delta calculation so the absolute tick values are
 * truncated to an integer.
 */
static void
userret(struct lwp *lp, struct trapframe *frame, int sticks)
{
	struct proc *p = lp->lwp_proc;
	void (*hook)(void);
	int sig;

	if (p->p_userret != NULL) {
		hook = p->p_userret;
		p->p_userret = NULL;
		(*hook)();
	}
		
	/*
	 * Charge system time if profiling.  Note: times are in microseconds.
	 * This may do a copyout and block, so do it first even though it
	 * means some system time will be charged as user time.
	 */
	if (p->p_flags & P_PROFIL) {
		addupc_task(p, frame->tf_eip, 
			(u_int)((int)lp->lwp_thread->td_sticks - sticks));
	}

recheck:
	/*
	 * If the jungle wants us dead, so be it.
	 */
	if (lp->lwp_mpflags & LWP_MP_WEXIT) {
		lwkt_gettoken(&p->p_token);
		lwp_exit(0);
		lwkt_reltoken(&p->p_token);	/* NOT REACHED */
	}

	/*
	 * Block here if we are in a stopped state.
	 */
	if (p->p_stat == SSTOP || dump_stop_usertds) {
		lwkt_gettoken(&p->p_token);
		tstop();
		lwkt_reltoken(&p->p_token);
		goto recheck;
	}

	/*
	 * Post any pending upcalls.  If running a virtual kernel be sure
	 * to restore the virtual kernel's vmspace before posting the upcall.
	 */
	if (p->p_flags & (P_SIGVTALRM | P_SIGPROF | P_UPCALLPEND)) {
		lwkt_gettoken(&p->p_token);
		if (p->p_flags & P_SIGVTALRM) {
			p->p_flags &= ~P_SIGVTALRM;
			ksignal(p, SIGVTALRM);
		}
		if (p->p_flags & P_SIGPROF) {
			p->p_flags &= ~P_SIGPROF;
			ksignal(p, SIGPROF);
		}
		if (p->p_flags & P_UPCALLPEND) {
			p->p_flags &= ~P_UPCALLPEND;
			postupcall(lp);
		}
		lwkt_reltoken(&p->p_token);
		goto recheck;
	}

	/*
	 * Post any pending signals.  If running a virtual kernel be sure
	 * to restore the virtual kernel's vmspace before posting the signal.
	 *
	 * WARNING!  postsig() can exit and not return.
	 */
	if ((sig = CURSIG_TRACE(lp)) != 0) {
		lwkt_gettoken(&p->p_token);
		postsig(sig);
		lwkt_reltoken(&p->p_token);
		goto recheck;
	}

	/*
	 * block here if we are swapped out, but still process signals
	 * (such as SIGKILL).  proc0 (the swapin scheduler) is already
	 * aware of our situation, we do not have to wake it up.
	 */
	if (p->p_flags & P_SWAPPEDOUT) {
		lwkt_gettoken(&p->p_token);
		get_mplock();
		p->p_flags |= P_SWAPWAIT;
		swapin_request();
		if (p->p_flags & P_SWAPWAIT)
			tsleep(p, PCATCH, "SWOUT", 0);
		p->p_flags &= ~P_SWAPWAIT;
		rel_mplock();
		lwkt_reltoken(&p->p_token);
		goto recheck;
	}

	/*
	 * In a multi-threaded program it is possible for a thread to change
	 * signal state during a system call which temporarily changes the
	 * signal mask.  In this case postsig() might not be run and we
	 * have to restore the mask ourselves.
	 */
	if (lp->lwp_flags & LWP_OLDMASK) {
		lp->lwp_flags &= ~LWP_OLDMASK;
		lp->lwp_sigmask = lp->lwp_oldsigmask;
		goto recheck;
	}
}

/*
 * Cleanup from userenter and any passive release that might have occured.
 * We must reclaim the current-process designation before we can return
 * to usermode.  We also handle both LWKT and USER reschedule requests.
 */
static __inline void
userexit(struct lwp *lp)
{
	struct thread *td = lp->lwp_thread;
	/* globaldata_t gd = td->td_gd; */

	/*
	 * Handle stop requests at kernel priority.  Any requests queued
	 * after this loop will generate another AST.
	 */
	while (lp->lwp_proc->p_stat == SSTOP) {
		lwkt_gettoken(&lp->lwp_proc->p_token);
		tstop();
		lwkt_reltoken(&lp->lwp_proc->p_token);
	}

	/*
	 * Become the current user scheduled process if we aren't already,
	 * and deal with reschedule requests and other factors.
	 */
	lp->lwp_proc->p_usched->acquire_curproc(lp);
	/* WARNING: we may have migrated cpu's */
	/* gd = td->td_gd; */

	/*
	 * Reduce our priority in preparation for a return to userland.  If
	 * our passive release function was still in place, our priority was
	 * never raised and does not need to be reduced.
	 */
	lwkt_passive_recover(td);
}

#if !defined(KTR_KERNENTRY)
#define	KTR_KERNENTRY	KTR_ALL
#endif
KTR_INFO_MASTER(kernentry);
KTR_INFO(KTR_KERNENTRY, kernentry, trap, 0,
	 "TRAP(pid %d, tid %d, trapno %d, eva %lu)",
	 pid_t pid, lwpid_t tid,  register_t trapno, vm_offset_t eva);
KTR_INFO(KTR_KERNENTRY, kernentry, trap_ret, 0, "TRAP_RET(pid %d, tid %d)",
	 pid_t pid, lwpid_t tid);
KTR_INFO(KTR_KERNENTRY, kernentry, syscall, 0, "SYSC(pid %d, tid %d, nr %d)",
	 pid_t pid, lwpid_t tid,  register_t trapno);
KTR_INFO(KTR_KERNENTRY, kernentry, syscall_ret, 0, "SYSRET(pid %d, tid %d, err %d)",
	 pid_t pid, lwpid_t tid,  int err);
KTR_INFO(KTR_KERNENTRY, kernentry, fork_ret, 0, "FORKRET(pid %d, tid %d)",
	 pid_t pid, lwpid_t tid);

/*
 * Exception, fault, and trap interface to the kernel.
 * This common code is called from assembly language IDT gate entry
 * routines that prepare a suitable stack frame, and restore this
 * frame after the exception has been processed.
 *
 * This function is also called from doreti in an interlock to handle ASTs.
 * For example:  hardwareint->INTROUTINE->(set ast)->doreti->trap
 *
 * NOTE!  We have to retrieve the fault address prior to obtaining the
 * MP lock because get_mplock() may switch out.  YYY cr2 really ought
 * to be retrieved by the assembly code, not here.
 *
 * XXX gd_trap_nesting_level currently prevents lwkt_switch() from panicing
 * if an attempt is made to switch from a fast interrupt or IPI.  This is
 * necessary to properly take fatal kernel traps on SMP machines if 
 * get_mplock() has to block.
 */

void
trap(struct trapframe *frame)
{
	struct globaldata *gd = mycpu;
	struct thread *td = gd->gd_curthread;
	struct lwp *lp = td->td_lwp;
	struct proc *p;
	int sticks = 0;
	int i = 0, ucode = 0, type, code;
#ifdef SMP
	int have_mplock = 0;
#endif
#ifdef INVARIANTS
	int crit_count = td->td_critcount;
	lwkt_tokref_t curstop = td->td_toks_stop;
#endif
	vm_offset_t eva;

	p = td->td_proc;
#ifdef DDB
	/*
	 * We need to allow T_DNA faults when the debugger is active since
	 * some dumping paths do large bcopy() which use the floating
	 * point registers for faster copying.
	 */
	if (db_active && frame->tf_trapno != T_DNA) {
		eva = (frame->tf_trapno == T_PAGEFLT ? rcr2() : 0);
		++gd->gd_trap_nesting_level;
		MAKEMPSAFE(have_mplock);
		trap_fatal(frame, eva);
		--gd->gd_trap_nesting_level;
		goto out2;
	}
#endif

	eva = 0;
	++gd->gd_trap_nesting_level;
	if (frame->tf_trapno == T_PAGEFLT) {
		/*
		 * For some Cyrix CPUs, %cr2 is clobbered by interrupts.
		 * This problem is worked around by using an interrupt
		 * gate for the pagefault handler.  We are finally ready
		 * to read %cr2 and then must reenable interrupts.
		 *
		 * XXX this should be in the switch statement, but the
		 * NO_FOOF_HACK and VM86 goto and ifdefs obfuscate the
		 * flow of control too much for this to be obviously
		 * correct.
		 */
		eva = rcr2();
		cpu_enable_intr();
	}

	--gd->gd_trap_nesting_level;

	if (!(frame->tf_eflags & PSL_I)) {
		/*
		 * Buggy application or kernel code has disabled interrupts
		 * and then trapped.  Enabling interrupts now is wrong, but
		 * it is better than running with interrupts disabled until
		 * they are accidentally enabled later.
		 */
		type = frame->tf_trapno;
		if (ISPL(frame->tf_cs)==SEL_UPL || (frame->tf_eflags & PSL_VM)) {
			MAKEMPSAFE(have_mplock);
			kprintf(
			    "pid %ld (%s): trap %d with interrupts disabled\n",
			    (long)curproc->p_pid, curproc->p_comm, type);
		} else if (type != T_BPTFLT && type != T_TRCTRAP) {
			/*
			 * XXX not quite right, since this may be for a
			 * multiple fault in user mode.
			 */
			MAKEMPSAFE(have_mplock);
			kprintf("kernel trap %d with interrupts disabled\n",
			    type);
		}
		cpu_enable_intr();
	}

#if defined(I586_CPU) && !defined(NO_F00F_HACK)
restart:
#endif
	type = frame->tf_trapno;
	code = frame->tf_err;

	if (in_vm86call) {
		if (frame->tf_eflags & PSL_VM &&
		    (type == T_PROTFLT || type == T_STKFLT)) {
#ifdef SMP
			KKASSERT(get_mplock_count(curthread) > 0);
#endif
			i = vm86_emulate((struct vm86frame *)frame);
#ifdef SMP
			KKASSERT(get_mplock_count(curthread) > 0);
#endif
			if (i != 0) {
				/*
				 * returns to original process
				 */
#ifdef SMP
				vm86_trap((struct vm86frame *)frame,
					  have_mplock);
#else
				vm86_trap((struct vm86frame *)frame, 0);
#endif
				KKASSERT(0); /* NOT REACHED */
			}
			goto out2;
		}
		switch (type) {
			/*
			 * these traps want either a process context, or
			 * assume a normal userspace trap.
			 */
		case T_PROTFLT:
		case T_SEGNPFLT:
			trap_fatal(frame, eva);
			goto out2;
		case T_TRCTRAP:
			type = T_BPTFLT;	/* kernel breakpoint */
			/* FALL THROUGH */
		}
		goto kernel_trap;	/* normal kernel trap handling */
	}

        if ((ISPL(frame->tf_cs) == SEL_UPL) || (frame->tf_eflags & PSL_VM)) {
		/* user trap */

		KTR_LOG(kernentry_trap, p->p_pid, lp->lwp_tid,
			frame->tf_trapno, eva);

		userenter(td, p);

		sticks = (int)td->td_sticks;
		lp->lwp_md.md_regs = frame;

		switch (type) {
		case T_PRIVINFLT:	/* privileged instruction fault */
			i = SIGILL;
			ucode = ILL_PRVOPC;
			break;

		case T_BPTFLT:		/* bpt instruction fault */
		case T_TRCTRAP:		/* trace trap */
			frame->tf_eflags &= ~PSL_T;
			i = SIGTRAP;
			ucode = (type == T_TRCTRAP ? TRAP_TRACE : TRAP_BRKPT);
			break;

		case T_ARITHTRAP:	/* arithmetic trap */
			ucode = code;
			i = SIGFPE;
			break;

		case T_ASTFLT:		/* Allow process switch */
			mycpu->gd_cnt.v_soft++;
			if (mycpu->gd_reqflags & RQF_AST_OWEUPC) {
				atomic_clear_int(&mycpu->gd_reqflags,
						 RQF_AST_OWEUPC);
				addupc_task(p, p->p_prof.pr_addr,
					    p->p_prof.pr_ticks);
			}
			goto out;

			/*
			 * The following two traps can happen in
			 * vm86 mode, and, if so, we want to handle
			 * them specially.
			 */
		case T_PROTFLT:		/* general protection fault */
		case T_STKFLT:		/* stack fault */
			if (frame->tf_eflags & PSL_VM) {
				i = vm86_emulate((struct vm86frame *)frame);
				if (i == 0)
					goto out;
				break;
			}
			i = SIGBUS;
			ucode = (type == T_PROTFLT) ? BUS_OBJERR : BUS_ADRERR;
			break;
		case T_SEGNPFLT:	/* segment not present fault */
			i = SIGBUS;
			ucode = BUS_ADRERR;
			break;
		case T_TSSFLT:		/* invalid TSS fault */
		case T_DOUBLEFLT:	/* double fault */
		default:
			i = SIGBUS;
			ucode = BUS_OBJERR;
			break;

		case T_PAGEFLT:		/* page fault */
			i = trap_pfault(frame, TRUE, eva);
			if (i == -1)
				goto out;
#if defined(I586_CPU) && !defined(NO_F00F_HACK)
			if (i == -2)
				goto restart;
#endif
			if (i == 0)
				goto out;

			if (i == SIGSEGV)
				ucode = SEGV_MAPERR;
			else {
				i = SIGSEGV;
				ucode = SEGV_ACCERR;
			}
			break;

		case T_DIVIDE:		/* integer divide fault */
			ucode = FPE_INTDIV;
			i = SIGFPE;
			break;

#if NISA > 0
		case T_NMI:
			MAKEMPSAFE(have_mplock);
#ifdef POWERFAIL_NMI
			goto handle_powerfail;
#else /* !POWERFAIL_NMI */
			/* machine/parity/power fail/"kitchen sink" faults */
			if (isa_nmi(code) == 0) {
#ifdef DDB
				/*
				 * NMI can be hooked up to a pushbutton
				 * for debugging.
				 */
				if (ddb_on_nmi) {
					kprintf ("NMI ... going to debugger\n");
					kdb_trap (type, 0, frame);
				}
#endif /* DDB */
				goto out2;
			} else if (panic_on_nmi)
				panic("NMI indicates hardware failure");
			break;
#endif /* POWERFAIL_NMI */
#endif /* NISA > 0 */

		case T_OFLOW:		/* integer overflow fault */
			ucode = FPE_INTOVF;
			i = SIGFPE;
			break;

		case T_BOUND:		/* bounds check fault */
			ucode = FPE_FLTSUB;
			i = SIGFPE;
			break;

		case T_DNA:
			/*
			 * Virtual kernel intercept - pass the DNA exception
			 * to the virtual kernel if it asked to handle it.
			 * This occurs when the virtual kernel is holding
			 * onto the FP context for a different emulated
			 * process then the one currently running.
			 *
			 * We must still call npxdna() since we may have
			 * saved FP state that the virtual kernel needs
			 * to hand over to a different emulated process.
			 */
			if (lp->lwp_vkernel && lp->lwp_vkernel->ve &&
			    (td->td_pcb->pcb_flags & FP_VIRTFP)
			) {
				npxdna();
				break;
			}

#if NNPX > 0
			/* 
			 * The kernel may have switched out the FP unit's
			 * state, causing the user process to take a fault
			 * when it tries to use the FP unit.  Restore the
			 * state here
			 */
			if (npxdna())
				goto out;
#endif
			if (!pmath_emulate) {
				i = SIGFPE;
				ucode = FPE_FPU_NP_TRAP;
				break;
			}
			i = (*pmath_emulate)(frame);
			if (i == 0) {
				if (!(frame->tf_eflags & PSL_T))
					goto out2;
				frame->tf_eflags &= ~PSL_T;
				i = SIGTRAP;
			}
			/* else ucode = emulator_only_knows() XXX */
			break;

		case T_FPOPFLT:		/* FPU operand fetch fault */
			ucode = ILL_COPROC;
			i = SIGILL;
			break;

		case T_XMMFLT:		/* SIMD floating-point exception */
			ucode = 0; /* XXX */
			i = SIGFPE;
			break;
		}
	} else {
kernel_trap:
		/* kernel trap */

		switch (type) {
		case T_PAGEFLT:			/* page fault */
			trap_pfault(frame, FALSE, eva);
			goto out2;

		case T_DNA:
#if NNPX > 0
			/*
			 * The kernel may be using npx for copying or other
			 * purposes.
			 */
			if (npxdna())
				goto out2;
#endif
			break;

		case T_PROTFLT:		/* general protection fault */
		case T_SEGNPFLT:	/* segment not present fault */
			/*
			 * Invalid segment selectors and out of bounds
			 * %eip's and %esp's can be set up in user mode.
			 * This causes a fault in kernel mode when the
			 * kernel tries to return to user mode.  We want
			 * to get this fault so that we can fix the
			 * problem here and not have to check all the
			 * selectors and pointers when the user changes
			 * them.
			 */
#define	MAYBE_DORETI_FAULT(where, whereto)				\
	do {								\
		if (frame->tf_eip == (int)where) {			\
			frame->tf_eip = (int)whereto;			\
			goto out2;					\
		}							\
	} while (0)
			if (mycpu->gd_intr_nesting_level == 0) {
				/*
				 * Invalid %fs's and %gs's can be created using
				 * procfs or PT_SETREGS or by invalidating the
				 * underlying LDT entry.  This causes a fault
				 * in kernel mode when the kernel attempts to
				 * switch contexts.  Lose the bad context
				 * (XXX) so that we can continue, and generate
				 * a signal.
				 */
				MAYBE_DORETI_FAULT(doreti_iret,
						   doreti_iret_fault);
				MAYBE_DORETI_FAULT(doreti_popl_ds,
						   doreti_popl_ds_fault);
				MAYBE_DORETI_FAULT(doreti_popl_es,
						   doreti_popl_es_fault);
				MAYBE_DORETI_FAULT(doreti_popl_fs,
						   doreti_popl_fs_fault);
				MAYBE_DORETI_FAULT(doreti_popl_gs,
						   doreti_popl_gs_fault);

				/*
				 * NOTE: cpu doesn't push esp on kernel trap
				 */
				if (td->td_pcb->pcb_onfault &&
				    td->td_pcb->pcb_onfault_sp ==
				    (int)&frame->tf_esp) {
					frame->tf_eip = 
					    (register_t)td->td_pcb->pcb_onfault;
					goto out2;
				}
			}
			break;

		case T_TSSFLT:
			/*
			 * PSL_NT can be set in user mode and isn't cleared
			 * automatically when the kernel is entered.  This
			 * causes a TSS fault when the kernel attempts to
			 * `iret' because the TSS link is uninitialized.  We
			 * want to get this fault so that we can fix the
			 * problem here and not every time the kernel is
			 * entered.
			 */
			if (frame->tf_eflags & PSL_NT) {
				frame->tf_eflags &= ~PSL_NT;
				goto out2;
			}
			break;

		case T_TRCTRAP:	 /* trace trap */
			if (frame->tf_eip == (int)IDTVEC(syscall)) {
				/*
				 * We've just entered system mode via the
				 * syscall lcall.  Continue single stepping
				 * silently until the syscall handler has
				 * saved the flags.
				 */
				goto out2;
			}
			if (frame->tf_eip == (int)IDTVEC(syscall) + 1) {
				/*
				 * The syscall handler has now saved the
				 * flags.  Stop single stepping it.
				 */
				frame->tf_eflags &= ~PSL_T;
				goto out2;
			}
                        /*
                         * Ignore debug register trace traps due to
                         * accesses in the user's address space, which
                         * can happen under several conditions such as
                         * if a user sets a watchpoint on a buffer and
                         * then passes that buffer to a system call.
                         * We still want to get TRCTRAPS for addresses
                         * in kernel space because that is useful when
                         * debugging the kernel.
                         */
                        if (user_dbreg_trap()) {
                                /*
                                 * Reset breakpoint bits because the
                                 * processor doesn't
                                 */
                                load_dr6(rdr6() & 0xfffffff0);
                                goto out2;
                        }
			/*
			 * FALLTHROUGH (TRCTRAP kernel mode, kernel address)
			 */
		case T_BPTFLT:
			/*
			 * If DDB is enabled, let it handle the debugger trap.
			 * Otherwise, debugger traps "can't happen".
			 */
			ucode = TRAP_BRKPT;
#ifdef DDB
			MAKEMPSAFE(have_mplock);
			if (kdb_trap (type, 0, frame))
				goto out2;
#endif
			break;

#if NISA > 0
		case T_NMI:
			MAKEMPSAFE(have_mplock);
#ifdef POWERFAIL_NMI
#ifndef TIMER_FREQ
#  define TIMER_FREQ 1193182
#endif
	handle_powerfail:
		{
		  static unsigned lastalert = 0;

		  if(time_second - lastalert > 10)
		    {
		      log(LOG_WARNING, "NMI: power fail\n");
		      sysbeep(TIMER_FREQ/880, hz);
		      lastalert = time_second;
		    }
		    /* YYY mp count */
		  goto out2;
		}
#else /* !POWERFAIL_NMI */
			/* machine/parity/power fail/"kitchen sink" faults */
			if (isa_nmi(code) == 0) {
#ifdef DDB
				/*
				 * NMI can be hooked up to a pushbutton
				 * for debugging.
				 */
				if (ddb_on_nmi) {
					kprintf ("NMI ... going to debugger\n");
					kdb_trap (type, 0, frame);
				}
#endif /* DDB */
				goto out2;
			} else if (panic_on_nmi == 0)
				goto out2;
			/* FALL THROUGH */
#endif /* POWERFAIL_NMI */
#endif /* NISA > 0 */
		}

		MAKEMPSAFE(have_mplock);
		trap_fatal(frame, eva);
		goto out2;
	}

	/*
	 * Virtual kernel intercept - if the fault is directly related to a
	 * VM context managed by a virtual kernel then let the virtual kernel
	 * handle it.
	 */
	if (lp->lwp_vkernel && lp->lwp_vkernel->ve) {
		vkernel_trap(lp, frame);
		goto out;
	}

	/* Translate fault for emulators (e.g. Linux) */
	if (*p->p_sysent->sv_transtrap)
		i = (*p->p_sysent->sv_transtrap)(i, type);

	MAKEMPSAFE(have_mplock);
	trapsignal(lp, i, ucode);

#ifdef DEBUG
	if (type <= MAX_TRAP_MSG) {
		uprintf("fatal process exception: %s",
			trap_msg[type]);
		if ((type == T_PAGEFLT) || (type == T_PROTFLT))
			uprintf(", fault VA = 0x%lx", (u_long)eva);
		uprintf("\n");
	}
#endif

out:
	userret(lp, frame, sticks);
	userexit(lp);
out2:	;
#ifdef SMP
	if (have_mplock)
		rel_mplock();
#endif
	if (p != NULL && lp != NULL)
		KTR_LOG(kernentry_trap_ret, p->p_pid, lp->lwp_tid);
#ifdef INVARIANTS
	KASSERT(crit_count == td->td_critcount,
		("trap: critical section count mismatch! %d/%d",
		crit_count, td->td_pri));
	KASSERT(curstop == td->td_toks_stop,
		("trap: extra tokens held after trap! %zd/%zd",
		curstop - &td->td_toks_base,
		td->td_toks_stop - &td->td_toks_base));
#endif
}

int
trap_pfault(struct trapframe *frame, int usermode, vm_offset_t eva)
{
	vm_offset_t va;
	struct vmspace *vm = NULL;
	vm_map_t map = 0;
	int rv = 0;
	int fault_flags;
	vm_prot_t ftype;
	thread_t td = curthread;
	struct lwp *lp = td->td_lwp;

	va = trunc_page(eva);
	if (va >= KERNBASE) {
		/*
		 * Don't allow user-mode faults in kernel address space.
		 * An exception:  if the faulting address is the invalid
		 * instruction entry in the IDT, then the Intel Pentium
		 * F00F bug workaround was triggered, and we need to
		 * treat it is as an illegal instruction, and not a page
		 * fault.
		 */
#if defined(I586_CPU) && !defined(NO_F00F_HACK)
		if ((eva == (unsigned int)&idt[6]) && has_f00f_bug) {
			frame->tf_trapno = T_PRIVINFLT;
			return -2;
		}
#endif
		if (usermode)
			goto nogo;

		map = &kernel_map;
	} else {
		/*
		 * This is a fault on non-kernel virtual memory.
		 * vm is initialized above to NULL. If curproc is NULL
		 * or curproc->p_vmspace is NULL the fault is fatal.
		 */
		if (lp != NULL)
			vm = lp->lwp_vmspace;

		if (vm == NULL)
			goto nogo;

		map = &vm->vm_map;
	}

	if (frame->tf_err & PGEX_W)
		ftype = VM_PROT_WRITE;
	else
		ftype = VM_PROT_READ;

	if (map != &kernel_map) {
		/*
		 * Keep swapout from messing with us during this
		 *	critical time.
		 */
		PHOLD(lp->lwp_proc);

		/*
		 * Issue fault
		 */
		fault_flags = 0;
		if (usermode)
			fault_flags |= VM_FAULT_BURST;
		if (ftype & VM_PROT_WRITE)
			fault_flags |= VM_FAULT_DIRTY;
		else
			fault_flags |= VM_FAULT_NORMAL;
		rv = vm_fault(map, va, ftype, fault_flags);
		PRELE(lp->lwp_proc);
	} else {
		/*
		 * Don't have to worry about process locking or stacks in the
		 * kernel.
		 */
		rv = vm_fault(map, va, ftype, VM_FAULT_NORMAL);
	}
	if (rv == KERN_SUCCESS)
		return (0);
nogo:
	if (!usermode) {
		/*
		 * NOTE: cpu doesn't push esp on kernel trap
		 */
		if (td->td_gd->gd_intr_nesting_level == 0 &&
		    td->td_pcb->pcb_onfault &&
		    td->td_pcb->pcb_onfault_sp == (int)&frame->tf_esp) {
			frame->tf_eip = (register_t)td->td_pcb->pcb_onfault;
			return (0);
		}
		if (td->td_gd->gd_intr_nesting_level == 0 &&
		    td->td_pcb->pcb_onfault) {
			kprintf("ESP mismatch %p %08x\n",
				&frame->tf_esp, td->td_pcb->pcb_onfault_sp);
		}
		trap_fatal(frame, eva);
		return (-1);
	}

	/* kludge to pass faulting virtual address to sendsig */
	frame->tf_xflags = frame->tf_err;
	frame->tf_err = eva;

	return((rv == KERN_PROTECTION_FAILURE) ? SIGBUS : SIGSEGV);
}

static void
trap_fatal(struct trapframe *frame, vm_offset_t eva)
{
	int code, type, ss, esp;
	struct soft_segment_descriptor softseg;

	code = frame->tf_err;
	type = frame->tf_trapno;
	sdtossd(&gdt[mycpu->gd_cpuid * NGDT + IDXSEL(frame->tf_cs & 0xffff)].sd, &softseg);

	if (type <= MAX_TRAP_MSG)
		kprintf("\n\nFatal trap %d: %s while in %s mode\n",
			type, trap_msg[type],
        		frame->tf_eflags & PSL_VM ? "vm86" :
			ISPL(frame->tf_cs) == SEL_UPL ? "user" : "kernel");
#ifdef SMP
	/* three separate prints in case of a trap on an unmapped page */
	kprintf("cpuid = %d; ", mycpu->gd_cpuid);
	kprintf("lapic.id = %08x\n", lapic->id);
#endif
	if (type == T_PAGEFLT) {
		kprintf("fault virtual address	= %p\n", (void *)eva);
		kprintf("fault code		= %s %s, %s\n",
			code & PGEX_U ? "user" : "supervisor",
			code & PGEX_W ? "write" : "read",
			code & PGEX_P ? "protection violation" : "page not present");
	}
	kprintf("instruction pointer	= 0x%x:0x%x\n",
	       frame->tf_cs & 0xffff, frame->tf_eip);
        if ((ISPL(frame->tf_cs) == SEL_UPL) || (frame->tf_eflags & PSL_VM)) {
		ss = frame->tf_ss & 0xffff;
		esp = frame->tf_esp;
	} else {
		ss = GSEL(GDATA_SEL, SEL_KPL);
		esp = (int)&frame->tf_esp;
	}
	kprintf("stack pointer	        = 0x%x:0x%x\n", ss, esp);
	kprintf("frame pointer	        = 0x%x:0x%x\n", ss, frame->tf_ebp);
	kprintf("code segment		= base 0x%x, limit 0x%x, type 0x%x\n",
	       softseg.ssd_base, softseg.ssd_limit, softseg.ssd_type);
	kprintf("			= DPL %d, pres %d, def32 %d, gran %d\n",
	       softseg.ssd_dpl, softseg.ssd_p, softseg.ssd_def32,
	       softseg.ssd_gran);
	kprintf("processor eflags	= ");
	if (frame->tf_eflags & PSL_T)
		kprintf("trace trap, ");
	if (frame->tf_eflags & PSL_I)
		kprintf("interrupt enabled, ");
	if (frame->tf_eflags & PSL_NT)
		kprintf("nested task, ");
	if (frame->tf_eflags & PSL_RF)
		kprintf("resume, ");
	if (frame->tf_eflags & PSL_VM)
		kprintf("vm86, ");
	kprintf("IOPL = %d\n", (frame->tf_eflags & PSL_IOPL) >> 12);
	kprintf("current process		= ");
	if (curproc) {
		kprintf("%lu (%s)\n",
		    (u_long)curproc->p_pid, curproc->p_comm ?
		    curproc->p_comm : "");
	} else {
		kprintf("Idle\n");
	}
	kprintf("current thread          = pri %d ", curthread->td_pri);
	if (curthread->td_critcount)
		kprintf("(CRIT)");
	kprintf("\n");
#ifdef SMP
/**
 *  XXX FIXME:
 *	we probably SHOULD have stopped the other CPUs before now!
 *	another CPU COULD have been touching cpl at this moment...
 */
	kprintf(" <- SMP: XXX");
#endif
	kprintf("\n");

#ifdef KDB
	if (kdb_trap(&psl))
		return;
#endif
#ifdef DDB
	if ((debugger_on_panic || db_active) && kdb_trap(type, code, frame))
		return;
#endif
	kprintf("trap number		= %d\n", type);
	if (type <= MAX_TRAP_MSG)
		panic("%s", trap_msg[type]);
	else
		panic("unknown/reserved trap");
}

/*
 * Double fault handler. Called when a fault occurs while writing
 * a frame for a trap/exception onto the stack. This usually occurs
 * when the stack overflows (such is the case with infinite recursion,
 * for example).
 *
 * XXX Note that the current PTD gets replaced by IdlePTD when the
 * task switch occurs. This means that the stack that was active at
 * the time of the double fault is not available at <kstack> unless
 * the machine was idle when the double fault occurred. The downside
 * of this is that "trace <ebp>" in ddb won't work.
 */
static __inline
int
in_kstack_guard(register_t rptr)
{
	thread_t td = curthread;

	if ((char *)rptr >= td->td_kstack &&
	    (char *)rptr < td->td_kstack + PAGE_SIZE) {
		return 1;
	}
	return 0;
}

void
dblfault_handler(void)
{
	struct mdglobaldata *gd = mdcpu;

	if (in_kstack_guard(gd->gd_common_tss.tss_esp) ||
	    in_kstack_guard(gd->gd_common_tss.tss_ebp)) {
		kprintf("DOUBLE FAULT - KERNEL STACK GUARD HIT!\n");
	} else {
		kprintf("DOUBLE FAULT:\n");
	}
	kprintf("eip = 0x%x\n", gd->gd_common_tss.tss_eip);
	kprintf("esp = 0x%x\n", gd->gd_common_tss.tss_esp);
	kprintf("ebp = 0x%x\n", gd->gd_common_tss.tss_ebp);
#ifdef SMP
	/* three separate prints in case of a trap on an unmapped page */
	kprintf("cpuid = %d; ", gd->mi.gd_cpuid);
	kprintf("lapic.id = %08x\n", lapic->id);
#endif
	panic("double fault");
}

/*
 * syscall2 -	MP aware system call request C handler
 *
 * A system call is essentially treated as a trap.  The MP lock is not
 * held on entry or return.  We are responsible for handling ASTs
 * (e.g. a task switch) prior to return.
 *
 * MPSAFE
 */
void
syscall2(struct trapframe *frame)
{
	struct thread *td = curthread;
	struct proc *p = td->td_proc;
	struct lwp *lp = td->td_lwp;
	caddr_t params;
	struct sysent *callp;
	register_t orig_tf_eflags;
	int sticks;
	int error;
	int narg;
#ifdef INVARIANTS
	int crit_count = td->td_critcount;
#endif
#ifdef SMP
	int have_mplock = 0;
#endif
	u_int code;
	union sysunion args;

#ifdef DIAGNOSTIC
	if (ISPL(frame->tf_cs) != SEL_UPL) {
		get_mplock();
		panic("syscall");
		/* NOT REACHED */
	}
#endif

	KTR_LOG(kernentry_syscall, p->p_pid, lp->lwp_tid,
		frame->tf_eax);

	userenter(td, p);	/* lazy raise our priority */

	/*
	 * Misc
	 */
	sticks = (int)td->td_sticks;
	orig_tf_eflags = frame->tf_eflags;

	/*
	 * Virtual kernel intercept - if a VM context managed by a virtual
	 * kernel issues a system call the virtual kernel handles it, not us.
	 * Restore the virtual kernel context and return from its system
	 * call.  The current frame is copied out to the virtual kernel.
	 */
	if (lp->lwp_vkernel && lp->lwp_vkernel->ve) {
		vkernel_trap(lp, frame);
		error = EJUSTRETURN;
		callp = NULL;
		goto out;
	}

	/*
	 * Get the system call parameters and account for time
	 */
	lp->lwp_md.md_regs = frame;
	params = (caddr_t)frame->tf_esp + sizeof(int);
	code = frame->tf_eax;

	if (p->p_sysent->sv_prepsyscall) {
		(*p->p_sysent->sv_prepsyscall)(
			frame, (int *)(&args.nosys.sysmsg + 1),
			&code, &params);
	} else {
		/*
		 * Need to check if this is a 32 bit or 64 bit syscall.
		 * fuword is MP aware.
		 */
		if (code == SYS_syscall) {
			/*
			 * Code is first argument, followed by actual args.
			 */
			code = fuword(params);
			params += sizeof(int);
		} else if (code == SYS___syscall) {
			/*
			 * Like syscall, but code is a quad, so as to maintain
			 * quad alignment for the rest of the arguments.
			 */
			code = fuword(params);
			params += sizeof(quad_t);
		}
	}

	code &= p->p_sysent->sv_mask;

	if (code >= p->p_sysent->sv_size)
		callp = &p->p_sysent->sv_table[0];
	else
		callp = &p->p_sysent->sv_table[code];

	narg = callp->sy_narg & SYF_ARGMASK;

#if 0
	if (p->p_sysent->sv_name[0] == 'L')
		kprintf("Linux syscall, code = %d\n", code);
#endif

	/*
	 * copyin is MP aware, but the tracing code is not
	 */
	if (narg && params) {
		error = copyin(params, (caddr_t)(&args.nosys.sysmsg + 1),
				narg * sizeof(register_t));
		if (error) {
#ifdef KTRACE
			if (KTRPOINT(td, KTR_SYSCALL)) {
				MAKEMPSAFE(have_mplock);
				
				ktrsyscall(lp, code, narg,
					(void *)(&args.nosys.sysmsg + 1));
			}
#endif
			goto bad;
		}
	}

#ifdef KTRACE
	if (KTRPOINT(td, KTR_SYSCALL)) {
		MAKEMPSAFE(have_mplock);
		ktrsyscall(lp, code, narg, (void *)(&args.nosys.sysmsg + 1));
	}
#endif

	/*
	 * For traditional syscall code edx is left untouched when 32 bit
	 * results are returned.  Since edx is loaded from fds[1] when the 
	 * system call returns we pre-set it here.
	 */
	args.sysmsg_fds[0] = 0;
	args.sysmsg_fds[1] = frame->tf_edx;

	/*
	 * The syscall might manipulate the trap frame. If it does it
	 * will probably return EJUSTRETURN.
	 */
	args.sysmsg_frame = frame;

	STOPEVENT(p, S_SCE, narg);	/* MP aware */

	/*
	 * NOTE: All system calls run MPSAFE now.  The system call itself
	 *	 is responsible for getting the MP lock.
	 */
	error = (*callp->sy_call)(&args);

out:
	/*
	 * MP SAFE (we may or may not have the MP lock at this point)
	 */
	switch (error) {
	case 0:
		/*
		 * Reinitialize proc pointer `p' as it may be different
		 * if this is a child returning from fork syscall.
		 */
		p = curproc;
		lp = curthread->td_lwp;
		frame->tf_eax = args.sysmsg_fds[0];
		frame->tf_edx = args.sysmsg_fds[1];
		frame->tf_eflags &= ~PSL_C;
		break;
	case ERESTART:
		/*
		 * Reconstruct pc, assuming lcall $X,y is 7 bytes,
		 * int 0x80 is 2 bytes. We saved this in tf_err.
		 */
		frame->tf_eip -= frame->tf_err;
		break;
	case EJUSTRETURN:
		break;
	case EASYNC:
		panic("Unexpected EASYNC return value (for now)");
	default:
bad:
		if (p->p_sysent->sv_errsize) {
			if (error >= p->p_sysent->sv_errsize)
				error = -1;	/* XXX */
			else
				error = p->p_sysent->sv_errtbl[error];
		}
		frame->tf_eax = error;
		frame->tf_eflags |= PSL_C;
		break;
	}

	/*
	 * Traced syscall.  trapsignal() is not MP aware.
	 */
	if ((orig_tf_eflags & PSL_T) && !(orig_tf_eflags & PSL_VM)) {
		MAKEMPSAFE(have_mplock);
		frame->tf_eflags &= ~PSL_T;
		trapsignal(lp, SIGTRAP, TRAP_TRACE);
	}

	/*
	 * Handle reschedule and other end-of-syscall issues
	 */
	userret(lp, frame, sticks);

#ifdef KTRACE
	if (KTRPOINT(td, KTR_SYSRET)) {
		MAKEMPSAFE(have_mplock);
		ktrsysret(lp, code, error, args.sysmsg_result);
	}
#endif

	/*
	 * This works because errno is findable through the
	 * register set.  If we ever support an emulation where this
	 * is not the case, this code will need to be revisited.
	 */
	STOPEVENT(p, S_SCX, code);

	userexit(lp);
#ifdef SMP
	/*
	 * Release the MP lock if we had to get it
	 */
	if (have_mplock)
		rel_mplock();
#endif
	KTR_LOG(kernentry_syscall_ret, p->p_pid, lp->lwp_tid, error);
#ifdef INVARIANTS
	KASSERT(crit_count == td->td_critcount,
		("syscall: critical section count mismatch! %d/%d",
		crit_count, td->td_pri));
	KASSERT(&td->td_toks_base == td->td_toks_stop,
		("syscall: extra tokens held after trap! %zd",
		td->td_toks_stop - &td->td_toks_base));
#endif
}

/*
 * NOTE: MP lock not held at any point.
 */
void
fork_return(struct lwp *lp, struct trapframe *frame)
{
	frame->tf_eax = 0;		/* Child returns zero */
	frame->tf_eflags &= ~PSL_C;	/* success */
	frame->tf_edx = 1;

	generic_lwp_return(lp, frame);
	KTR_LOG(kernentry_fork_ret, lp->lwp_proc->p_pid, lp->lwp_tid);
}

/*
 * Simplified back end of syscall(), used when returning from fork()
 * directly into user mode.
 *
 * This code will return back into the fork trampoline code which then
 * runs doreti.
 *
 * NOTE: The mplock is not held at any point.
 */
void
generic_lwp_return(struct lwp *lp, struct trapframe *frame)
{
	struct proc *p = lp->lwp_proc;

	/*
	 * Newly forked processes are given a kernel priority.  We have to
	 * adjust the priority to a normal user priority and fake entry
	 * into the kernel (call userenter()) to install a passive release
	 * function just in case userret() decides to stop the process.  This
	 * can occur when ^Z races a fork.  If we do not install the passive
	 * release function the current process designation will not be
	 * released when the thread goes to sleep.
	 */
	lwkt_setpri_self(TDPRI_USER_NORM);
	userenter(lp->lwp_thread, p);
	userret(lp, frame, 0);
#ifdef KTRACE
	if (KTRPOINT(lp->lwp_thread, KTR_SYSRET))
		ktrsysret(lp, SYS_fork, 0, 0);
#endif
	lp->lwp_flags |= LWP_PASSIVE_ACQ;
	userexit(lp);
	lp->lwp_flags &= ~LWP_PASSIVE_ACQ;
}

/*
 * If PGEX_FPFAULT is set then set FP_VIRTFP in the PCB to force a T_DNA
 * fault (which is then passed back to the virtual kernel) if an attempt is
 * made to use the FP unit.
 *
 * XXX this is a fairly big hack.
 */
void
set_vkernel_fp(struct trapframe *frame)
{
	struct thread *td = curthread;

	if (frame->tf_xflags & PGEX_FPFAULT) {
		td->td_pcb->pcb_flags |= FP_VIRTFP;
		if (mdcpu->gd_npxthread == td)
			npxexit();
	} else {
		td->td_pcb->pcb_flags &= ~FP_VIRTFP;
	}
}

/*
 * Called from vkernel_trap() to fixup the vkernel's syscall
 * frame for vmspace_ctl() return.
 */
void
cpu_vkernel_trap(struct trapframe *frame, int error)
{
	frame->tf_eax = error;
	if (error)
		frame->tf_eflags |= PSL_C;
	else
		frame->tf_eflags &= ~PSL_C;
}