fault.c

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/*
 *  linux/arch/m68k/mm/fault.c
 *
 *  Copyright (C) 1995  Hamish Macdonald
 */

#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/kernel.h>
#include <linux/ptrace.h>
#include <linux/interrupt.h>
#include <linux/module.h>

#include <asm/setup.h>
#include <asm/traps.h>
#include <asm/uaccess.h>
#include <asm/pgalloc.h>

extern void die_if_kernel(char *, struct pt_regs *, long);

int send_fault_sig(struct pt_regs *regs)
{
    siginfo_t siginfo = { 0, 0, 0, };

    siginfo.si_signo = current->thread.signo;
    siginfo.si_code = current->thread.code;
    siginfo.si_addr = (void *)current->thread.faddr;
#ifdef DEBUG
    printk("send_fault_sig: %p,%d,%d\n", siginfo.si_addr, siginfo.si_signo, siginfo.si_code);
#endif

    if (user_mode(regs)) {
        force_sig_info(siginfo.si_signo,
                   &siginfo, current);
    } else {
        if (handle_kernel_fault(regs))
            return -1;

        //if (siginfo.si_signo == SIGBUS)
        //  force_sig_info(siginfo.si_signo,
        //             &siginfo, current);

        /*
         * Oops. The kernel tried to access some bad page. We'll have to
         * terminate things with extreme prejudice.
         */
        if ((unsigned long)siginfo.si_addr < PAGE_SIZE)
            printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
        else
            printk(KERN_ALERT "Unable to handle kernel access");
        printk(" at virtual address %p\n", siginfo.si_addr);
        die_if_kernel("Oops", regs, 0 /*error_code*/);
        do_exit(SIGKILL);
    }

    return 1;
}

/*
 * This routine handles page faults.  It determines the problem, and
 * then passes it off to one of the appropriate routines.
 *
 * error_code:
 *  bit 0 == 0 means no page found, 1 means protection fault
 *  bit 1 == 0 means read, 1 means write
 *
 * If this routine detects a bad access, it returns 1, otherwise it
 * returns 0.
 */
int do_page_fault(struct pt_regs *regs, unsigned long address,
                  unsigned long error_code)
{
    struct mm_struct *mm = current->mm;
    struct vm_area_struct * vma;
    int fault;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

#ifdef DEBUG
    printk ("do page fault:\nregs->sr=%#x, regs->pc=%#lx, address=%#lx, %ld, %p\n",
        regs->sr, regs->pc, address, error_code,
        current->mm->pgd);
#endif

    /*
     * If we're in an interrupt or have no user
     * context, we must not take the fault..
     */
    if (in_atomic() || !mm)
        goto no_context;

retry:
    down_read(&mm->mmap_sem);

    vma = find_vma(mm, address);
    if (!vma)
        goto map_err;
    if (vma->vm_flags & VM_IO)
        goto acc_err;
    if (vma->vm_start <= address)
        goto good_area;
    if (!(vma->vm_flags & VM_GROWSDOWN))
        goto map_err;
    if (user_mode(regs)) {
        /* Accessing the stack below usp is always a bug.  The
           "+ 256" is there due to some instructions doing
           pre-decrement on the stack and that doesn't show up
           until later.  */
        if (address + 256 < rdusp())
            goto map_err;
    }
    if (expand_stack(vma, address))
        goto map_err;

/*
 * Ok, we have a good vm_area for this memory access, so
 * we can handle it..
 */
good_area:
#ifdef DEBUG
    printk("do_page_fault: good_area\n");
#endif
    switch (error_code & 3) {
        default:    /* 3: write, present */
            /* fall through */
        case 2:     /* write, not present */
            if (!(vma->vm_flags & VM_WRITE))
                goto acc_err;
            flags |= FAULT_FLAG_WRITE;
            break;
        case 1:     /* read, present */
            goto acc_err;
        case 0:     /* read, not present */
            if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                goto acc_err;
    }

    /*
     * If for any reason at all we couldn't handle the fault,
     * make sure we exit gracefully rather than endlessly redo
     * the fault.
     */

    fault = handle_mm_fault(mm, vma, address, flags);
#ifdef DEBUG
    printk("handle_mm_fault returns %d\n",fault);
#endif

    if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
        return 0;

    if (unlikely(fault & VM_FAULT_ERROR)) {
        if (fault & VM_FAULT_OOM)
            goto out_of_memory;
        else if (fault & VM_FAULT_SIGBUS)
            goto bus_err;
        BUG();
    }

    /*
     * Major/minor page fault accounting is only done on the
     * initial attempt. If we go through a retry, it is extremely
     * likely that the page will be found in page cache at that point.
     */
    if (flags & FAULT_FLAG_ALLOW_RETRY) {
        if (fault & VM_FAULT_MAJOR)
            current->maj_flt++;
        else
            current->min_flt++;
        if (fault & VM_FAULT_RETRY) {
            /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
             * of starvation. */
            flags &= ~FAULT_FLAG_ALLOW_RETRY;
            flags |= FAULT_FLAG_TRIED;

            /*
             * No need to up_read(&mm->mmap_sem) as we would
             * have already released it in __lock_page_or_retry
             * in mm/filemap.c.
             */

            goto retry;
        }
    }

    up_read(&mm->mmap_sem);
    return 0;

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
out_of_memory:
    up_read(&mm->mmap_sem);
    if (!user_mode(regs))
        goto no_context;
    pagefault_out_of_memory();
    return 0;

no_context:
    current->thread.signo = SIGBUS;
    current->thread.faddr = address;
    return send_fault_sig(regs);

bus_err:
    current->thread.signo = SIGBUS;
    current->thread.code = BUS_ADRERR;
    current->thread.faddr = address;
    goto send_sig;

map_err:
    current->thread.signo = SIGSEGV;
    current->thread.code = SEGV_MAPERR;
    current->thread.faddr = address;
    goto send_sig;

acc_err:
    current->thread.signo = SIGSEGV;
    current->thread.code = SEGV_ACCERR;
    current->thread.faddr = address;

send_sig:
    up_read(&mm->mmap_sem);
    return send_fault_sig(regs);
}