text: /*
   *  linux/kernel/vm86.c
   *
   *  Copyright (C) 1994  Linus Torvalds
   *
   *  29 dec 2001 - Fixed oopses caused by unchecked access to the vm86
   *                stack - Manfred Spraul <manfred@colorfullife.com>
   *
   *  22 mar 2002 - Manfred detected the stackfaults, but didn't handle
   *                them correctly. Now the emulation will be in a
   *                consistent state after stackfaults - Kasper Dupont
   *                <kasperd@daimi.au.dk>
   *
   *  22 mar 2002 - Added missing clear_IF in set_vflags_* Kasper Dupont
   *                <kasperd@daimi.au.dk>
   *
   *  ?? ??? 2002 - Fixed premature returns from handle_vm86_fault
   *                caused by Kasper Dupont's changes - Stas Sergeev
   *
   *   4 apr 2002 - Fixed CHECK_IF_IN_TRAP broken by Stas' changes.
   *                Kasper Dupont <kasperd@daimi.au.dk>
   *
   *   9 apr 2002 - Changed syntax of macros in handle_vm86_fault.
   *                Kasper Dupont <kasperd@daimi.au.dk>
   *
   *   9 apr 2002 - Changed stack access macros to jump to a label
   *                instead of returning to userspace. This simplifies
   *                do_int, and is needed by handle_vm6_fault. Kasper
   *                Dupont <kasperd@daimi.au.dk>
   *
   */
  
  #include <linux/capability.h>
  #include <linux/errno.h>
  #include <linux/interrupt.h>
  #include <linux/sched.h>
  #include <linux/kernel.h>
  #include <linux/signal.h>
  #include <linux/string.h>
  #include <linux/mm.h>
  #include <linux/smp.h>
  #include <linux/smp_lock.h>
  #include <linux/highmem.h>
  #include <linux/ptrace.h>
  #include <linux/audit.h>
  #include <linux/stddef.h>
  
  #include <asm/uaccess.h>
  #include <asm/io.h>
  #include <asm/tlbflush.h>
  #include <asm/irq.h>
  
  /*
   * Known problems:
   *
   * Interrupt handling is not guaranteed:
   * - a real x86 will disable all interrupts for one instruction
   *   after a "mov ss,xx" to make stack handling atomic even without
   *   the 'lss' instruction. We can't guarantee this in v86 mode,
   *   as the next instruction might result in a page fault or similar.
   * - a real x86 will have interrupts disabled for one instruction
   *   past the 'sti' that enables them. We don't bother with all the
   *   details yet.
   *
   * Let's hope these problems do not actually matter for anything.
   */
  
  
  #define KVM86	((struct kernel_vm86_struct *)regs)
  #define VMPI 	KVM86->vm86plus
  
  
  /*
   * 8- and 16-bit register defines..
   */
  #define AL(regs)	(((unsigned char *)&((regs)->pt.eax))[0])
  #define AH(regs)	(((unsigned char *)&((regs)->pt.eax))[1])
  #define IP(regs)	(*(unsigned short *)&((regs)->pt.eip))
  #define SP(regs)	(*(unsigned short *)&((regs)->pt.esp))
  
  /*
   * virtual flags (16 and 32-bit versions)
   */
  #define VFLAGS	(*(unsigned short *)&(current->thread.v86flags))
  #define VEFLAGS	(current->thread.v86flags)
  
  #define set_flags(X,new,mask) \
  ((X) = ((X) & ~(mask)) | ((new) & (mask)))
  
  #define SAFE_MASK	(0xDD5)
  #define RETURN_MASK	(0xDFF)
  
  /* convert kernel_vm86_regs to vm86_regs */
  static int copy_vm86_regs_to_user(struct vm86_regs __user *user,
  				  const struct kernel_vm86_regs *regs)
  {
  	int ret = 0;
  
  	/* kernel_vm86_regs is missing xgs, so copy everything up to
  	   (but not including) orig_eax, and then rest including orig_eax. */
  	ret += copy_to_user(user, regs, offsetof(struct kernel_vm86_regs, pt.orig_eax));
  	ret += copy_to_user(&user->orig_eax, &regs->pt.orig_eax,
  			    sizeof(struct kernel_vm86_regs) -
  			    offsetof(struct kernel_vm86_regs, pt.orig_eax));
  
  	return ret;
  }
  
  /* convert vm86_regs to kernel_vm86_regs */
  static int copy_vm86_regs_from_user(struct kernel_vm86_regs *regs,
  				    const struct vm86_regs __user *user,
  				    unsigned extra)
  {
  	int ret = 0;
  
  	/* copy eax-xfs inclusive */
  	ret += copy_from_user(regs, user, offsetof(struct kernel_vm86_regs, pt.orig_eax));
  	/* copy orig_eax-__gsh+extra */
  	ret += copy_from_user(&regs->pt.orig_eax, &user->orig_eax,
  			      sizeof(struct kernel_vm86_regs) -
  			      offsetof(struct kernel_vm86_regs, pt.orig_eax) +
  			      extra);
  	return ret;
  }
  
  struct pt_regs * FASTCALL(save_v86_state(struct kernel_vm86_regs * regs));
  struct pt_regs * fastcall save_v86_state(struct kernel_vm86_regs * regs)
  {
  	struct tss_struct *tss;
  	struct pt_regs *ret;
  	unsigned long tmp;
  
  	/*
  	 * This gets called from entry.S with interrupts disabled, but
  	 * from process context. Enable interrupts here, before trying
  	 * to access user space.
  	 */
  	local_irq_enable();
  
  	if (!current->thread.vm86_info) {
  		printk("no vm86_info: BAD\n");
  		do_exit(SIGSEGV);
  	}
  	set_flags(regs->pt.eflags, VEFLAGS, VIF_MASK | current->thread.v86mask);
  	tmp = copy_vm86_regs_to_user(&current->thread.vm86_info->regs,regs);
  	tmp += put_user(current->thread.screen_bitmap,&current->thread.vm86_info->screen_bitmap);
  	if (tmp) {
  		printk("vm86: could not access userspace vm86_info\n");
  		do_exit(SIGSEGV);
  	}
  
  	tss = &per_cpu(init_tss, get_cpu());
  	current->thread.esp0 = current->thread.saved_esp0;
  	current->thread.sysenter_cs = __KERNEL_CS;
  	load_esp0(tss, &current->thread);
  	current->thread.saved_esp0 = 0;
  	put_cpu();
  
  	ret = KVM86->regs32;
  
  	ret->xfs = current->thread.saved_fs;
  	loadsegment(gs, current->thread.saved_gs);
  
  	return ret;
  }
  
  static void mark_screen_rdonly(struct mm_struct *mm)
  {
  	pgd_t *pgd;
  	pud_t *pud;
  	pmd_t *pmd;
  	pte_t *pte;
  	spinlock_t *ptl;
  	int i;
  
  	pgd = pgd_offset(mm, 0xA0000);
  	if (pgd_none_or_clear_bad(pgd))
  		goto out;
  	pud = pud_offset(pgd, 0xA0000);
  	if (pud_none_or_clear_bad(pud))
  		goto out;
  	pmd = pmd_offset(pud, 0xA0000);
  	if (pmd_none_or_clear_bad(pmd))
  		goto out;
  	pte = pte_offset_map_lock(mm, pmd, 0xA0000, &ptl);
  	for (i = 0; i < 32; i++) {
  		if (pte_present(*pte))
  			set_pte(pte, pte_wrprotect(*pte));
  		pte++;
  	}
  	pte_unmap_unlock(pte, ptl);
  out:
  	flush_tlb();
  }
  
  
  
  static int do_vm86_irq_handling(int subfunction, int irqnumber);
  static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk);
  
  asmlinkage int sys_vm86old(struct pt_regs regs)
  {
  	struct vm86_struct __user *v86 = (struct vm86_struct __user *)regs.ebx;
  	struct kernel_vm86_struct info; /* declare this _on top_,
  					 * this avoids wasting of stack space.
  					 * This remains on the stack until we
  					 * return to 32 bit user space.
  					 */
  	struct task_struct *tsk;
  	int tmp, ret = -EPERM;
  
  	tsk = current;
  	if (tsk->thread.saved_esp0)
  		goto out;
  	tmp = copy_vm86_regs_from_user(&info.regs, &v86->regs,
  				       offsetof(struct kernel_vm86_struct, vm86plus) -
  				       sizeof(info.regs));
  	ret = -EFAULT;
  	if (tmp)
  		goto out;
  	memset(&info.vm86plus, 0, (int)&info.regs32 - (int)&info.vm86plus);
  	info.regs32 = &regs;
  	tsk->thread.vm86_info = v86;
  	do_sys_vm86(&info, tsk);
  	ret = 0;	/* we never return here */
  out:
  	return ret;
  }
  
  
  asmlinkage int sys_vm86(struct pt_regs regs)
  {
  	struct kernel_vm86_struct info; /* declare this _on top_,
  					 * this avoids wasting of stack space.
  					 * This remains on the stack until we
  					 * return to 32 bit user space.
  					 */
  	struct task_struct *tsk;
  	int tmp, ret;
  	struct vm86plus_struct __user *v86;
  
  	tsk = current;
  	switch (regs.ebx) {
  		case VM86_REQUEST_IRQ:
  		case VM86_FREE_IRQ:
  		case VM86_GET_IRQ_BITS:
  		case VM86_GET_AND_RESET_IRQ:
  			ret = do_vm86_irq_handling(regs.ebx, (int)regs.ecx);
  			goto out;
  		case VM86_PLUS_INSTALL_CHECK:
  			/* NOTE: on old vm86 stuff this will return the error
  			   from access_ok(), because the subfunction is
  			   interpreted as (invalid) address to vm86_struct.
  			   So the installation check works.
  			 */
  			ret = 0;
  			goto out;
  	}
  
  	/* we come here only for functions VM86_ENTER, VM86_ENTER_NO_BYPASS */
  	ret = -EPERM;
  	if (tsk->thread.saved_esp0)
  		goto out;
  	v86 = (struct vm86plus_struct __user *)regs.ecx;
  	tmp = copy_vm86_regs_from_user(&info.regs, &v86->regs,
  				       offsetof(struct kernel_vm86_struct, regs32) -
  				       sizeof(info.regs));
  	ret = -EFAULT;
  	if (tmp)
  		goto out;
  	info.regs32 = &regs;
  	info.vm86plus.is_vm86pus = 1;
  	tsk->thread.vm86_info = (struct vm86_struct __user *)v86;
  	do_sys_vm86(&info, tsk);
  	ret = 0;	/* we never return here */
  out:
  	return ret;
  }
  
  
  static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk)
  {
  	struct tss_struct *tss;
  /*
   * make sure the vm86() system call doesn't try to do anything silly
   */
  	info->regs.pt.xds = 0;
  	info->regs.pt.xes = 0;
  	info->regs.pt.xfs = 0;
  
  /* we are clearing gs later just before "jmp resume_userspace",
   * because it is not saved/restored.
   */
  
  /*
   * The eflags register is also special: we cannot trust that the user
   * has set it up safely, so this makes sure interrupt etc flags are
   * inherited from protected mode.
   */
   	VEFLAGS = info->regs.pt.eflags;
  	info->regs.pt.eflags &= SAFE_MASK;
  	info->regs.pt.eflags |= info->regs32->eflags & ~SAFE_MASK;
  	info->regs.pt.eflags |= VM_MASK;
  
  	switch (info->cpu_type) {
  		case CPU_286:
  			tsk->thread.v86mask = 0;
  			break;
  		case CPU_386:
  			tsk->thread.v86mask = NT_MASK | IOPL_MASK;
  			break;
  		case CPU_486:
  			tsk->thread.v86mask = AC_MASK | NT_MASK | IOPL_MASK;
  			break;
  		default:
  			tsk->thread.v86mask = ID_MASK | AC_MASK | NT_MASK | IOPL_MASK;
  			break;
  	}
  
  /*
   * Save old state, set default return value (%eax) to 0
   */
  	info->regs32->eax = 0;
  	tsk->thread.saved_esp0 = tsk->thread.esp0;
  	tsk->thread.saved_fs = info->regs32->xfs;
  	savesegment(gs, tsk->thread.saved_gs);
  
  	tss = &per_cpu(init_tss, get_cpu());
  	tsk->thread.esp0 = (unsigned long) &info->VM86_TSS_ESP0;
  	if (cpu_has_sep)
  		tsk->thread.sysenter_cs = 0;
  	load_esp0(tss, &tsk->thread);
  	put_cpu();
  
  	tsk->thread.screen_bitmap = info->screen_bitmap;
  	if (info->flags & VM86_SCREEN_BITMAP)
  		mark_screen_rdonly(tsk->mm);
  
  	/*call audit_syscall_exit since we do not exit via the normal paths */
  	if (unlikely(current->audit_context))
  		audit_syscall_exit(AUDITSC_RESULT(0), 0);
  
  	__asm__ __volatile__(
  		"movl %0,%%esp\n\t"
  		"movl %1,%%ebp\n\t"
  		"mov  %2, %%gs\n\t"
  		"jmp resume_userspace"
  		: /* no outputs */
  		:"r" (&info->regs), "r" (task_thread_info(tsk)), "r" (0));
  	/* we never return here */
  }
  
  static inline void return_to_32bit(struct kernel_vm86_regs * regs16, int retval)
  {
  	struct pt_regs * regs32;
  
  	regs32 = save_v86_state(regs16);
  	regs32->eax = retval;
  	__asm__ __volatile__("movl %0,%%esp\n\t"
  		"movl %1,%%ebp\n\t"
  		"jmp resume_userspace"
  		: : "r" (regs32), "r" (current_thread_info()));
  }
  
  static inline void set_IF(struct kernel_vm86_regs * regs)
  {
  	VEFLAGS |= VIF_MASK;
  	if (VEFLAGS & VIP_MASK)
  		return_to_32bit(regs, VM86_STI);
  }
  
  static inline void clear_IF(struct kernel_vm86_regs * regs)
  {
  	VEFLAGS &= ~VIF_MASK;
  }
  
  static inline void clear_TF(struct kernel_vm86_regs * regs)
  {
  	regs->pt.eflags &= ~TF_MASK;
  }
  
  static inline void clear_AC(struct kernel_vm86_regs * regs)
  {
  	regs->pt.eflags &= ~AC_MASK;
  }
  
  /* It is correct to call set_IF(regs) from the set_vflags_*
   * functions. However someone forgot to call clear_IF(regs)
   * in the opposite case.
   * After the command sequence CLI PUSHF STI POPF you should
   * end up with interrups disabled, but you ended up with
   * interrupts enabled.
   *  ( I was testing my own changes, but the only bug I
   *    could find was in a function I had not changed. )
   * [KD]
   */
  
  static inline void set_vflags_long(unsigned long eflags, struct kernel_vm86_regs * regs)
  {
  	set_flags(VEFLAGS, eflags, current->thread.v86mask);
  	set_flags(regs->pt.eflags, eflags, SAFE_MASK);
  	if (eflags & IF_MASK)
  		set_IF(regs);
  	else
  		clear_IF(regs);
  }
  
  static inline void set_vflags_short(unsigned short flags, struct kernel_vm86_regs * regs)
  {
  	set_flags(VFLAGS, flags, current->thread.v86mask);
  	set_flags(regs->pt.eflags, flags, SAFE_MASK);
  	if (flags & IF_MASK)
  		set_IF(regs);
  	else
  		clear_IF(regs);
  }
  
  static inline unsigned long get_vflags(struct kernel_vm86_regs * regs)
  {
  	unsigned long flags = regs->pt.eflags & RETURN_MASK;
  
  	if (VEFLAGS & VIF_MASK)
  		flags |= IF_MASK;
  	flags |= IOPL_MASK;
  	return flags | (VEFLAGS & current->thread.v86mask);
  }
  
  static inline int is_revectored(int nr, struct revectored_struct * bitmap)
  {
  	__asm__ __volatile__("btl %2,%1\n\tsbbl %0,%0"
  		:"=r" (nr)
  		:"m" (*bitmap),"r" (nr));
  	return nr;
  }
  
  #define val_byte(val, n) (((__u8 *)&val)[n])
  
  #define pushb(base, ptr, val, err_label) \
  	do { \
  		__u8 __val = val; \
  		ptr--; \
  		if (put_user(__val, base + ptr) < 0) \
  			goto err_label; \
  	} while(0)
  
  #define pushw(base, ptr, val, err_label) \
  	do { \
  		__u16 __val = val; \
  		ptr--; \
  		if (put_user(val_byte(__val, 1), base + ptr) < 0) \
  			goto err_label; \
  		ptr--; \
  		if (put_user(val_byte(__val, 0), base + ptr) < 0) \
  			goto err_label; \
  	} while(0)
  
  #define pushl(base, ptr, val, err_label) \
  	do { \
  		__u32 __val = val; \
  		ptr--; \
  		if (put_user(val_byte(__val, 3), base + ptr) < 0) \
  			goto err_label; \
  		ptr--; \
  		if (put_user(val_byte(__val, 2), base + ptr) < 0) \
  			goto err_label; \
  		ptr--; \
  		if (put_user(val_byte(__val, 1), base + ptr) < 0) \
  			goto err_label; \
  		ptr--; \
  		if (put_user(val_byte(__val, 0), base + ptr) < 0) \
  			goto err_label; \
  	} while(0)
  
  #define popb(base, ptr, err_label) \
  	({ \
  		__u8 __res; \
  		if (get_user(__res, base + ptr) < 0) \
  			goto err_label; \
  		ptr++; \
  		__res; \
  	})
  
  #define popw(base, ptr, err_label) \
  	({ \
  		__u16 __res; \
  		if (get_user(val_byte(__res, 0), base + ptr) < 0) \
  			goto err_label; \
  		ptr++; \
  		if (get_user(val_byte(__res, 1), base + ptr) < 0) \
  			goto err_label; \
  		ptr++; \
  		__res; \
  	})
  
  #define popl(base, ptr, err_label) \
  	({ \
  		__u32 __res; \
  		if (get_user(val_byte(__res, 0), base + ptr) < 0) \
  			goto err_label; \
  		ptr++; \
  		if (get_user(val_byte(__res, 1), base + ptr) < 0) \
  			goto err_label; \
  		ptr++; \
  		if (get_user(val_byte(__res, 2), base + ptr) < 0) \
  			goto err_label; \
  		ptr++; \
  		if (get_user(val_byte(__res, 3), base + ptr) < 0) \
  			goto err_label; \
  		ptr++; \
  		__res; \
  	})
  
  /* There are so many possible reasons for this function to return
   * VM86_INTx, so adding another doesn't bother me. We can expect
   * userspace programs to be able to handle it. (Getting a problem
   * in userspace is always better than an Oops anyway.) [KD]
   */
  static void do_int(struct kernel_vm86_regs *regs, int i,
      unsigned char __user * ssp, unsigned short sp)
  {
  	unsigned long __user *intr_ptr;
  	unsigned long segoffs;
  
  	if (regs->pt.xcs == BIOSSEG)
  		goto cannot_handle;
  	if (is_revectored(i, &KVM86->int_revectored))
  		goto cannot_handle;
  	if (i==0x21 && is_revectored(AH(regs),&KVM86->int21_revectored))
  		goto cannot_handle;
  	intr_ptr = (unsigned long __user *) (i << 2);
  	if (get_user(segoffs, intr_ptr))
  		goto cannot_handle;
  	if ((segoffs >> 16) == BIOSSEG)
  		goto cannot_handle;
  	pushw(ssp, sp, get_vflags(regs), cannot_handle);
  	pushw(ssp, sp, regs->pt.xcs, cannot_handle);
  	pushw(ssp, sp, IP(regs), cannot_handle);
  	regs->pt.xcs = segoffs >> 16;
  	SP(regs) -= 6;
  	IP(regs) = segoffs & 0xffff;
  	clear_TF(regs);
  	clear_IF(regs);
  	clear_AC(regs);
  	return;
  
  cannot_handle:
  	return_to_32bit(regs, VM86_INTx + (i << 8));
  }
  
  int handle_vm86_trap(struct kernel_vm86_regs * regs, long error_code, int trapno)
  {
  	if (VMPI.is_vm86pus) {
  		if ( (trapno==3) || (trapno==1) )
  			return_to_32bit(regs, VM86_TRAP + (trapno << 8));
  		do_int(regs, trapno, (unsigned char __user *) (regs->pt.xss << 4), SP(regs));
  		return 0;
  	}
  	if (trapno !=1)
  		return 1; /* we let this handle by the calling routine */
  	if (current->ptrace & PT_PTRACED) {
  		unsigned long flags;
  		spin_lock_irqsave(&current->sighand->siglock, flags);
  		sigdelset(&current->blocked, SIGTRAP);
  		recalc_sigpending();
  		spin_unlock_irqrestore(&current->sighand->siglock, flags);
  	}
  	send_sig(SIGTRAP, current, 1);
  	current->thread.trap_no = trapno;
  	current->thread.error_code = error_code;
  	return 0;
  }
  
  void handle_vm86_fault(struct kernel_vm86_regs * regs, long error_code)
  {
  	unsigned char opcode;
  	unsigned char __user *csp;
  	unsigned char __user *ssp;
  	unsigned short ip, sp, orig_flags;
  	int data32, pref_done;
  
  #define CHECK_IF_IN_TRAP \
  	if (VMPI.vm86dbg_active && VMPI.vm86dbg_TFpendig) \
  		newflags |= TF_MASK
  #define VM86_FAULT_RETURN do { \
  	if (VMPI.force_return_for_pic  && (VEFLAGS & (IF_MASK | VIF_MASK))) \
  		return_to_32bit(regs, VM86_PICRETURN); \
  	if (orig_flags & TF_MASK) \
  		handle_vm86_trap(regs, 0, 1); \
  	return; } while (0)
  
  	orig_flags = *(unsigned short *)&regs->pt.eflags;
  
  	csp = (unsigned char __user *) (regs->pt.xcs << 4);
  	ssp = (unsigned char __user *) (regs->pt.xss << 4);
  	sp = SP(regs);
  	ip = IP(regs);
  
  	data32 = 0;
  	pref_done = 0;
  	do {
  		switch (opcode = popb(csp, ip, simulate_sigsegv)) {
  			case 0x66:      /* 32-bit data */     data32=1; break;
  			case 0x67:      /* 32-bit address */  break;
  			case 0x2e:      /* CS */              break;
  			case 0x3e:      /* DS */              break;
  			case 0x26:      /* ES */              break;
  			case 0x36:      /* SS */              break;
  			case 0x65:      /* GS */              break;
  			case 0x64:      /* FS */              break;
  			case 0xf2:      /* repnz */       break;
  			case 0xf3:      /* rep */             break;
  			default: pref_done = 1;
  		}
  	} while (!pref_done);
  
  	switch (opcode) {
  
  	/* pushf */
  	case 0x9c:
  		if (data32) {
  			pushl(ssp, sp, get_vflags(regs), simulate_sigsegv);
  			SP(regs) -= 4;
  		} else {
  			pushw(ssp, sp, get_vflags(regs), simulate_sigsegv);
  			SP(regs) -= 2;
  		}
  		IP(regs) = ip;
  		VM86_FAULT_RETURN;
  
  	/* popf */
  	case 0x9d:
  		{
  		unsigned long newflags;
  		if (data32) {
  			newflags=popl(ssp, sp, simulate_sigsegv);
  			SP(regs) += 4;
  		} else {
  			newflags = popw(ssp, sp, simulate_sigsegv);
  			SP(regs) += 2;
  		}
  		IP(regs) = ip;
  		CHECK_IF_IN_TRAP;
  		if (data32) {
  			set_vflags_long(newflags, regs);
  		} else {
  			set_vflags_short(newflags, regs);
  		}
  		VM86_FAULT_RETURN;
  		}
  
  	/* int xx */
  	case 0xcd: {
  		int intno=popb(csp, ip, simulate_sigsegv);
  		IP(regs) = ip;
  		if (VMPI.vm86dbg_active) {
  			if ( (1 << (intno &7)) & VMPI.vm86dbg_intxxtab[intno >> 3] )
  				return_to_32bit(regs, VM86_INTx + (intno << 8));
  		}
  		do_int(regs, intno, ssp, sp);
  		return;
  	}
  
  	/* iret */
  	case 0xcf:
  		{
  		unsigned long newip;
  		unsigned long newcs;
  		unsigned long newflags;
  		if (data32) {
  			newip=popl(ssp, sp, simulate_sigsegv);
  			newcs=popl(ssp, sp, simulate_sigsegv);
  			newflags=popl(ssp, sp, simulate_sigsegv);
  			SP(regs) += 12;
  		} else {
  			newip = popw(ssp, sp, simulate_sigsegv);
  			newcs = popw(ssp, sp, simulate_sigsegv);
  			newflags = popw(ssp, sp, simulate_sigsegv);
  			SP(regs) += 6;
  		}
  		IP(regs) = newip;
  		regs->pt.xcs = newcs;
  		CHECK_IF_IN_TRAP;
  		if (data32) {
  			set_vflags_long(newflags, regs);
  		} else {
  			set_vflags_short(newflags, regs);
  		}
  		VM86_FAULT_RETURN;
  		}
  
  	/* cli */
  	case 0xfa:
  		IP(regs) = ip;
  		clear_IF(regs);
  		VM86_FAULT_RETURN;
  
  	/* sti */
  	/*
  	 * Damn. This is incorrect: the 'sti' instruction should actually
  	 * enable interrupts after the /next/ instruction. Not good.
  	 *
  	 * Probably needs some horsing around with the TF flag. Aiee..
  	 */
  	case 0xfb:
  		IP(regs) = ip;
  		set_IF(regs);
  		VM86_FAULT_RETURN;
  
  	default:
  		return_to_32bit(regs, VM86_UNKNOWN);
  	}
  
  	return;
  
  simulate_sigsegv:
  	/* FIXME: After a long discussion with Stas we finally
  	 *        agreed, that this is wrong. Here we should
  	 *        really send a SIGSEGV to the user program.
  	 *        But how do we create the correct context? We
  	 *        are inside a general protection fault handler
  	 *        and has just returned from a page fault handler.
  	 *        The correct context for the signal handler
  	 *        should be a mixture of the two, but how do we
  	 *        get the information? [KD]
  	 */
  	return_to_32bit(regs, VM86_UNKNOWN);
  }
  
  /* ---------------- vm86 special IRQ passing stuff ----------------- */
  
  #define VM86_IRQNAME		"vm86irq"
  
  static struct vm86_irqs {
  	struct task_struct *tsk;
  	int sig;
  } vm86_irqs[16];
  
  static DEFINE_SPINLOCK(irqbits_lock);
  static int irqbits;
  
  #define ALLOWED_SIGS ( 1 /* 0 = don't send a signal */ \
  	| (1 << SIGUSR1) | (1 << SIGUSR2) | (1 << SIGIO)  | (1 << SIGURG) \
  	| (1 << SIGUNUSED) )
  	
  static irqreturn_t irq_handler(int intno, void *dev_id)
  {
  	int irq_bit;
  	unsigned long flags;
  
  	spin_lock_irqsave(&irqbits_lock, flags);	
  	irq_bit = 1 << intno;
  	if ((irqbits & irq_bit) || ! vm86_irqs[intno].tsk)
  		goto out;
  	irqbits |= irq_bit;
  	if (vm86_irqs[intno].sig)
  		send_sig(vm86_irqs[intno].sig, vm86_irqs[intno].tsk, 1);
  	/*
  	 * IRQ will be re-enabled when user asks for the irq (whether
  	 * polling or as a result of the signal)
  	 */
  	disable_irq_nosync(intno);
  	spin_unlock_irqrestore(&irqbits_lock, flags);
  	return IRQ_HANDLED;
  
  out:
  	spin_unlock_irqrestore(&irqbits_lock, flags);	
  	return IRQ_NONE;
  }
  
  static inline void free_vm86_irq(int irqnumber)
  {
  	unsigned long flags;
  
  	free_irq(irqnumber, NULL);
  	vm86_irqs[irqnumber].tsk = NULL;
  
  	spin_lock_irqsave(&irqbits_lock, flags);	
  	irqbits &= ~(1 << irqnumber);
  	spin_unlock_irqrestore(&irqbits_lock, flags);	
  }
  
  void release_vm86_irqs(struct task_struct *task)
  {
  	int i;
  	for (i = FIRST_VM86_IRQ ; i <= LAST_VM86_IRQ; i++)
  	    if (vm86_irqs[i].tsk == task)
  		free_vm86_irq(i);
  }
  
  static inline int get_and_reset_irq(int irqnumber)
  {
  	int bit;
  	unsigned long flags;
  	int ret = 0;
  	
  	if (invalid_vm86_irq(irqnumber)) return 0;
  	if (vm86_irqs[irqnumber].tsk != current) return 0;
  	spin_lock_irqsave(&irqbits_lock, flags);	
  	bit = irqbits & (1 << irqnumber);
  	irqbits &= ~bit;
  	if (bit) {
  		enable_irq(irqnumber);
  		ret = 1;
  	}
  
  	spin_unlock_irqrestore(&irqbits_lock, flags);	
  	return ret;
  }
  
  
  static int do_vm86_irq_handling(int subfunction, int irqnumber)
  {
  	int ret;
  	switch (subfunction) {
  		case VM86_GET_AND_RESET_IRQ: {
  			return get_and_reset_irq(irqnumber);
  		}
  		case VM86_GET_IRQ_BITS: {
  			return irqbits;
  		}
  		case VM86_REQUEST_IRQ: {
  			int sig = irqnumber >> 8;
  			int irq = irqnumber & 255;
  			if (!capable(CAP_SYS_ADMIN)) return -EPERM;
  			if (!((1 << sig) & ALLOWED_SIGS)) return -EPERM;
  			if (invalid_vm86_irq(irq)) return -EPERM;
  			if (vm86_irqs[irq].tsk) return -EPERM;
  			ret = request_irq(irq, &irq_handler, 0, VM86_IRQNAME, NULL);
  			if (ret) return ret;
  			vm86_irqs[irq].sig = sig;
  			vm86_irqs[irq].tsk = current;
  			return irq;
  		}
  		case  VM86_FREE_IRQ: {
  			if (invalid_vm86_irq(irqnumber)) return -EPERM;
  			if (!vm86_irqs[irqnumber].tsk) return 0;
  			if (vm86_irqs[irqnumber].tsk != current) return -EPERM;
  			free_vm86_irq(irqnumber);
  			return 0;
  		}
  	}
  	return -EINVAL;
  }
  
  