fault.c

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/*
 * Copyright (C) 2004-2006 Atmel Corporation
 *
 * Based on linux/arch/sh/mm/fault.c:
 *   Copyright (C) 1999  Niibe Yutaka
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/kdebug.h>
#include <linux/kprobes.h>

#include <asm/mmu_context.h>
#include <asm/sysreg.h>
#include <asm/tlb.h>
#include <asm/uaccess.h>

#ifdef CONFIG_KPROBES
static inline int notify_page_fault(struct pt_regs *regs, int trap)
{
    int ret = 0;

    if (!user_mode(regs)) {
        if (kprobe_running() && kprobe_fault_handler(regs, trap))
            ret = 1;
    }

    return ret;
}
#else
static inline int notify_page_fault(struct pt_regs *regs, int trap)
{
    return 0;
}
#endif

int exception_trace = 1;

/*
 * This routine handles page faults. It determines the address and the
 * problem, and then passes it off to one of the appropriate routines.
 *
 * ecr is the Exception Cause Register. Possible values are:
 *   6:  Protection fault (instruction access)
 *   15: Protection fault (read access)
 *   16: Protection fault (write access)
 *   20: Page not found (instruction access)
 *   24: Page not found (read access)
 *   28: Page not found (write access)
 */
asmlinkage void do_page_fault(unsigned long ecr, struct pt_regs *regs)
{
    struct task_struct *tsk;
    struct mm_struct *mm;
    struct vm_area_struct *vma;
    const struct exception_table_entry *fixup;
    unsigned long address;
    unsigned long page;
    long signr;
    int code;
    int fault;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

    if (notify_page_fault(regs, ecr))
        return;

    address = sysreg_read(TLBEAR);

    tsk = current;
    mm = tsk->mm;

    signr = SIGSEGV;
    code = SEGV_MAPERR;

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

    local_irq_enable();

retry:
    down_read(&mm->mmap_sem);

    vma = find_vma(mm, address);
    if (!vma)
        goto bad_area;
    if (vma->vm_start <= address)
        goto good_area;
    if (!(vma->vm_flags & VM_GROWSDOWN))
        goto bad_area;
    if (expand_stack(vma, address))
        goto bad_area;

    /*
     * Ok, we have a good vm_area for this memory access, so we
     * can handle it...
     */
good_area:
    code = SEGV_ACCERR;

    switch (ecr) {
    case ECR_PROTECTION_X:
    case ECR_TLB_MISS_X:
        if (!(vma->vm_flags & VM_EXEC))
            goto bad_area;
        break;
    case ECR_PROTECTION_R:
    case ECR_TLB_MISS_R:
        if (!(vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)))
            goto bad_area;
        break;
    case ECR_PROTECTION_W:
    case ECR_TLB_MISS_W:
        if (!(vma->vm_flags & VM_WRITE))
            goto bad_area;
        flags |= FAULT_FLAG_WRITE;
        break;
    default:
        panic("Unhandled case %lu in do_page_fault!", ecr);
    }

    /*
     * 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);

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

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

    if (flags & FAULT_FLAG_ALLOW_RETRY) {
        if (fault & VM_FAULT_MAJOR)
            tsk->maj_flt++;
        else
            tsk->min_flt++;
        if (fault & VM_FAULT_RETRY) {
            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;

    /*
     * Something tried to access memory that isn't in our memory
     * map. Fix it, but check if it's kernel or user first...
     */
bad_area:
    up_read(&mm->mmap_sem);

    if (user_mode(regs)) {
        if (exception_trace && printk_ratelimit())
            printk("%s%s[%d]: segfault at %08lx pc %08lx "
                   "sp %08lx ecr %lu\n",
                   is_global_init(tsk) ? KERN_EMERG : KERN_INFO,
                   tsk->comm, tsk->pid, address, regs->pc,
                   regs->sp, ecr);
        _exception(SIGSEGV, regs, code, address);
        return;
    }

no_context:
    /* Are we prepared to handle this kernel fault? */
    fixup = search_exception_tables(regs->pc);
    if (fixup) {
        regs->pc = fixup->fixup;
        return;
    }

    /*
     * Oops. The kernel tried to access some bad page. We'll have
     * to terminate things with extreme prejudice.
     */
    if (address < PAGE_SIZE)
        printk(KERN_ALERT
               "Unable to handle kernel NULL pointer dereference");
    else
        printk(KERN_ALERT
               "Unable to handle kernel paging request");
    printk(" at virtual address %08lx\n", address);

    page = sysreg_read(PTBR);
    printk(KERN_ALERT "ptbr = %08lx", page);
    if (address >= TASK_SIZE)
        page = (unsigned long)swapper_pg_dir;
    if (page) {
        page = ((unsigned long *)page)[address >> 22];
        printk(" pgd = %08lx", page);
        if (page & _PAGE_PRESENT) {
            page &= PAGE_MASK;
            address &= 0x003ff000;
            page = ((unsigned long *)__va(page))[address >> PAGE_SHIFT];
            printk(" pte = %08lx", page);
        }
    }
    printk("\n");
    die("Kernel access of bad area", regs, signr);
    return;

    /*
     * 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);
    pagefault_out_of_memory();
    if (!user_mode(regs))
        goto no_context;
    return;

do_sigbus:
    up_read(&mm->mmap_sem);

    /* Kernel mode? Handle exceptions or die */
    signr = SIGBUS;
    code = BUS_ADRERR;
    if (!user_mode(regs))
        goto no_context;

    if (exception_trace)
        printk("%s%s[%d]: bus error at %08lx pc %08lx "
               "sp %08lx ecr %lu\n",
               is_global_init(tsk) ? KERN_EMERG : KERN_INFO,
               tsk->comm, tsk->pid, address, regs->pc,
               regs->sp, ecr);

    _exception(SIGBUS, regs, BUS_ADRERR, address);
}

asmlinkage void do_bus_error(unsigned long addr, int write_access,
                 struct pt_regs *regs)
{
    printk(KERN_ALERT
           "Bus error at physical address 0x%08lx (%s access)\n",
           addr, write_access ? "write" : "read");
    printk(KERN_INFO "DTLB dump:\n");
    dump_dtlb();
    die("Bus Error", regs, SIGKILL);
}