mm: revert "page-writeback.c: subtract min_free_kbytes from dirtyable memory"

[linux/fpc-iii.git] / arch / x86 / kernel / vm86_32.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>
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/capability.h>
#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/syscalls.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/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.ax))[0])
#define AH(regs)        (((unsigned char *)&((regs)->pt.ax))[1])
#define IP(regs)        (*(unsigned short *)&((regs)->pt.ip))
#define SP(regs)        (*(unsigned short *)&((regs)->pt.sp))

/*
 * 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 gs, 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_ax));
        ret += copy_to_user(&user->orig_eax, &regs->pt.orig_ax,
                            sizeof(struct kernel_vm86_regs) -
                            offsetof(struct kernel_vm86_regs, pt.orig_ax));

        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 ax-fs inclusive */
        ret += copy_from_user(regs, user, offsetof(struct kernel_vm86_regs, pt.orig_ax));
        /* copy orig_ax-__gsh+extra */
        ret += copy_from_user(&regs->pt.orig_ax, &user->orig_eax,
                              sizeof(struct kernel_vm86_regs) -
                              offsetof(struct kernel_vm86_regs, pt.orig_ax) +
                              extra);
        return ret;
}

struct pt_regs *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) {
                pr_alert("no vm86_info: BAD\n");
                do_exit(SIGSEGV);
        }
        set_flags(regs->pt.flags, VEFLAGS, X86_EFLAGS_VIF | 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) {
                pr_alert("could not access userspace vm86_info\n");
                do_exit(SIGSEGV);
        }

        tss = &per_cpu(init_tss, get_cpu());
        current->thread.sp0 = current->thread.saved_sp0;
        current->thread.sysenter_cs = __KERNEL_CS;
        load_sp0(tss, &current->thread);
        current->thread.saved_sp0 = 0;
        put_cpu();

        ret = KVM86->regs32;

        ret->fs = current->thread.saved_fs;
        set_user_gs(ret, 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;

        down_write(&mm->mmap_sem);
        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);
        split_huge_page_pmd_mm(mm, 0xA0000, pmd);
        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:
        up_write(&mm->mmap_sem);
        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);

SYSCALL_DEFINE1(vm86old, struct vm86_struct __user *, v86)
{
        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 = current;
        int tmp;

        if (tsk->thread.saved_sp0)
                return -EPERM;
        tmp = copy_vm86_regs_from_user(&info.regs, &v86->regs,
                                       offsetof(struct kernel_vm86_struct, vm86plus) -
                                       sizeof(info.regs));
        if (tmp)
                return -EFAULT;
        memset(&info.vm86plus, 0, (int)&info.regs32 - (int)&info.vm86plus);
        info.regs32 = current_pt_regs();
        tsk->thread.vm86_info = v86;
        do_sys_vm86(&info, tsk);
        return 0;       /* we never return here */
}


SYSCALL_DEFINE2(vm86, unsigned long, cmd, unsigned long, arg)
{
        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;
        struct vm86plus_struct __user *v86;

        tsk = current;
        switch (cmd) {
        case VM86_REQUEST_IRQ:
        case VM86_FREE_IRQ:
        case VM86_GET_IRQ_BITS:
        case VM86_GET_AND_RESET_IRQ:
                return do_vm86_irq_handling(cmd, (int)arg);
        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.
                 */
                return 0;
        }

        /* we come here only for functions VM86_ENTER, VM86_ENTER_NO_BYPASS */
        if (tsk->thread.saved_sp0)
                return -EPERM;
        v86 = (struct vm86plus_struct __user *)arg;
        tmp = copy_vm86_regs_from_user(&info.regs, &v86->regs,
                                       offsetof(struct kernel_vm86_struct, regs32) -
                                       sizeof(info.regs));
        if (tmp)
                return -EFAULT;
        info.regs32 = current_pt_regs();
        info.vm86plus.is_vm86pus = 1;
        tsk->thread.vm86_info = (struct vm86_struct __user *)v86;
        do_sys_vm86(&info, tsk);
        return 0;       /* we never return here */
}


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.ds = 0;
        info->regs.pt.es = 0;
        info->regs.pt.fs = 0;
#ifndef CONFIG_X86_32_LAZY_GS
        info->regs.pt.gs = 0;
#endif

/*
 * The flags 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.flags;
        info->regs.pt.flags &= SAFE_MASK;
        info->regs.pt.flags |= info->regs32->flags & ~SAFE_MASK;
        info->regs.pt.flags |= X86_VM_MASK;

        switch (info->cpu_type) {
        case CPU_286:
                tsk->thread.v86mask = 0;
                break;
        case CPU_386:
                tsk->thread.v86mask = X86_EFLAGS_NT | X86_EFLAGS_IOPL;
                break;
        case CPU_486:
                tsk->thread.v86mask = X86_EFLAGS_AC | X86_EFLAGS_NT | X86_EFLAGS_IOPL;
                break;
        default:
                tsk->thread.v86mask = X86_EFLAGS_ID | X86_EFLAGS_AC | X86_EFLAGS_NT | X86_EFLAGS_IOPL;
                break;
        }

/*
 * Save old state, set default return value (%ax) to 0 (VM86_SIGNAL)
 */
        info->regs32->ax = VM86_SIGNAL;
        tsk->thread.saved_sp0 = tsk->thread.sp0;
        tsk->thread.saved_fs = info->regs32->fs;
        tsk->thread.saved_gs = get_user_gs(info->regs32);

        tss = &per_cpu(init_tss, get_cpu());
        tsk->thread.sp0 = (unsigned long) &info->VM86_TSS_ESP0;
        if (cpu_has_sep)
                tsk->thread.sysenter_cs = 0;
        load_sp0(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 */
#ifdef CONFIG_AUDITSYSCALL
        if (unlikely(current->audit_context))
                __audit_syscall_exit(1, 0);
#endif

        __asm__ __volatile__(
                "movl %0,%%esp\n\t"
                "movl %1,%%ebp\n\t"
#ifdef CONFIG_X86_32_LAZY_GS
                "mov  %2, %%gs\n\t"
#endif
                "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->ax = 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 |= X86_EFLAGS_VIF;
        if (VEFLAGS & X86_EFLAGS_VIP)
                return_to_32bit(regs, VM86_STI);
}

static inline void clear_IF(struct kernel_vm86_regs *regs)
{
        VEFLAGS &= ~X86_EFLAGS_VIF;
}

static inline void clear_TF(struct kernel_vm86_regs *regs)
{
        regs->pt.flags &= ~X86_EFLAGS_TF;
}

static inline void clear_AC(struct kernel_vm86_regs *regs)
{
        regs->pt.flags &= ~X86_EFLAGS_AC;
}

/*
 * 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 interrupts 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 flags, struct kernel_vm86_regs *regs)
{
        set_flags(VEFLAGS, flags, current->thread.v86mask);
        set_flags(regs->pt.flags, flags, SAFE_MASK);
        if (flags & X86_EFLAGS_IF)
                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.flags, flags, SAFE_MASK);
        if (flags & X86_EFLAGS_IF)
                set_IF(regs);
        else
                clear_IF(regs);
}

static inline unsigned long get_vflags(struct kernel_vm86_regs *regs)
{
        unsigned long flags = regs->pt.flags & RETURN_MASK;

        if (VEFLAGS & X86_EFLAGS_VIF)
                flags |= X86_EFLAGS_IF;
        flags |= X86_EFLAGS_IOPL;
        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.cs == 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.cs, cannot_handle);
        pushw(ssp, sp, IP(regs), cannot_handle);
        regs->pt.cs = 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)) {
                        KVM86->regs32->ax = VM86_TRAP + (trapno << 8);
                        /* setting this flag forces the code in entry_32.S to
                           the path where we call save_v86_state() and change
                           the stack pointer to KVM86->regs32 */
                        set_thread_flag(TIF_NOTIFY_RESUME);
                        return 0;
                }
                do_int(regs, trapno, (unsigned char __user *) (regs->pt.ss << 4), SP(regs));
                return 0;
        }
        if (trapno != 1)
                return 1; /* we let this handle by the calling routine */
        current->thread.trap_nr = trapno;
        current->thread.error_code = error_code;
        force_sig(SIGTRAP, current);
        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 |= X86_EFLAGS_TF
#define VM86_FAULT_RETURN do { \
        if (VMPI.force_return_for_pic  && (VEFLAGS & (X86_EFLAGS_IF | X86_EFLAGS_VIF))) \
                return_to_32bit(regs, VM86_PICRETURN); \
        if (orig_flags & X86_EFLAGS_TF) \
                handle_vm86_trap(regs, 0, 1); \
        return; } while (0)

        orig_flags = *(unsigned short *)&regs->pt.flags;

        csp = (unsigned char __user *) (regs->pt.cs << 4);
        ssp = (unsigned char __user *) (regs->pt.ss << 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.cs = 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;
}