fault.c

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/*
 *  arch/cris/mm/fault.c
 *
 *  Copyright (C) 2000-2010  Axis Communications AB
 */

#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/wait.h>
#include <asm/uaccess.h>
#include <arch/system.h>

extern int find_fixup_code(struct pt_regs *);
extern void die_if_kernel(const char *, struct pt_regs *, long);
extern void show_registers(struct pt_regs *regs);

/* debug of low-level TLB reload */
#undef DEBUG

#ifdef DEBUG
#define D(x) x
#else
#define D(x)
#endif

/* debug of higher-level faults */
#define DPG(x)

/* current active page directory */

DEFINE_PER_CPU(pgd_t *, current_pgd);
unsigned long cris_signal_return_page;

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * Notice that the address we're given is aligned to the page the fault
 * occurred in, since we only get the PFN in R_MMU_CAUSE not the complete
 * address.
 *
 * 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.
 */

asmlinkage void
do_page_fault(unsigned long address, struct pt_regs *regs,
          int protection, int writeaccess)
{
    struct task_struct *tsk;
    struct mm_struct *mm;
    struct vm_area_struct * vma;
    siginfo_t info;
    int fault;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
                ((writeaccess & 1) ? FAULT_FLAG_WRITE : 0);

    D(printk(KERN_DEBUG
         "Page fault for %lX on %X at %lX, prot %d write %d\n",
         address, smp_processor_id(), instruction_pointer(regs),
         protection, writeaccess));

    tsk = current;

    /*
     * We fault-in kernel-space virtual memory on-demand. The
     * 'reference' page table is init_mm.pgd.
     *
     * NOTE! We MUST NOT take any locks for this case. We may
     * be in an interrupt or a critical region, and should
     * only copy the information from the master page table,
     * nothing more.
     *
     * NOTE2: This is done so that, when updating the vmalloc
     * mappings we don't have to walk all processes pgdirs and
     * add the high mappings all at once. Instead we do it as they
     * are used. However vmalloc'ed page entries have the PAGE_GLOBAL
     * bit set so sometimes the TLB can use a lingering entry.
     *
     * This verifies that the fault happens in kernel space
     * and that the fault was not a protection error (error_code & 1).
     */

    if (address >= VMALLOC_START &&
        !protection &&
        !user_mode(regs))
        goto vmalloc_fault;

    /* When stack execution is not allowed we store the signal
     * trampolines in the reserved cris_signal_return_page.
     * Handle this in the exact same way as vmalloc (we know
     * that the mapping is there and is valid so no need to
     * call handle_mm_fault).
     */
    if (cris_signal_return_page &&
        address == cris_signal_return_page &&
        !protection && user_mode(regs))
        goto vmalloc_fault;

    /* we can and should enable interrupts at this point */
    local_irq_enable();

    mm = tsk->mm;
    info.si_code = SEGV_MAPERR;

    /*
     * If we're in an interrupt or "atomic" operation 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 bad_area;
    if (vma->vm_start <= address)
        goto good_area;
    if (!(vma->vm_flags & VM_GROWSDOWN))
        goto bad_area;
    if (user_mode(regs)) {
        /*
         * accessing the stack below usp is always a bug.
         * we get page-aligned addresses so we can only check
         * if we're within a page from usp, but that might be
         * enough to catch brutal errors at least.
         */
        if (address + PAGE_SIZE < rdusp())
            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:
    info.si_code = SEGV_ACCERR;

    /* first do some preliminary protection checks */

    if (writeaccess == 2){
        if (!(vma->vm_flags & VM_EXEC))
            goto bad_area;
    } else if (writeaccess == 1) {
        if (!(vma->vm_flags & VM_WRITE))
            goto bad_area;
    } else {
        if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
            goto bad_area;
    }

    /*
     * 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);

 bad_area_nosemaphore:
    DPG(show_registers(regs));

    /* User mode accesses just cause a SIGSEGV */

    if (user_mode(regs)) {
        printk(KERN_NOTICE "%s (pid %d) segfaults for page "
            "address %08lx at pc %08lx\n",
            tsk->comm, tsk->pid,
            address, instruction_pointer(regs));

        /* With DPG on, we've already dumped registers above.  */
        DPG(if (0))
            show_registers(regs);

#ifdef CONFIG_NO_SEGFAULT_TERMINATION
        DECLARE_WAIT_QUEUE_HEAD(wq);
        wait_event_interruptible(wq, 0 == 1);
#else
        info.si_signo = SIGSEGV;
        info.si_errno = 0;
        /* info.si_code has been set above */
        info.si_addr = (void *)address;
        force_sig_info(SIGSEGV, &info, tsk);
#endif
        return;
    }

 no_context:

    /* Are we prepared to handle this kernel fault?
     *
     * (The kernel has valid exception-points in the source
     *  when it accesses user-memory. When it fails in one
     *  of those points, we find it in a table and do a jump
     *  to some fixup code that loads an appropriate error
     *  code)
     */

    if (find_fixup_code(regs))
        return;

    /*
     * Oops. The kernel tried to access some bad page. We'll have to
     * terminate things with extreme prejudice.
     */

    if (!oops_in_progress) {
        oops_in_progress = 1;
        if ((unsigned long) (address) < PAGE_SIZE)
            printk(KERN_ALERT "Unable to handle kernel NULL "
                "pointer dereference");
        else
            printk(KERN_ALERT "Unable to handle kernel access"
                " at virtual address %08lx\n", address);

        die_if_kernel("Oops", regs, (writeaccess << 1) | protection);
        oops_in_progress = 0;
    }

    do_exit(SIGKILL);

    /*
     * 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;

 do_sigbus:
    up_read(&mm->mmap_sem);

    /*
     * Send a sigbus, regardless of whether we were in kernel
     * or user mode.
     */
    info.si_signo = SIGBUS;
    info.si_errno = 0;
    info.si_code = BUS_ADRERR;
    info.si_addr = (void *)address;
    force_sig_info(SIGBUS, &info, tsk);

    /* Kernel mode? Handle exceptions or die */
    if (!user_mode(regs))
        goto no_context;
    return;

vmalloc_fault:
    {
        /*
         * Synchronize this task's top level page-table
         * with the 'reference' page table.
         *
         * Use current_pgd instead of tsk->active_mm->pgd
         * since the latter might be unavailable if this
         * code is executed in a misfortunately run irq
         * (like inside schedule() between switch_mm and
         *  switch_to...).
         */

        int offset = pgd_index(address);
        pgd_t *pgd, *pgd_k;
        pud_t *pud, *pud_k;
        pmd_t *pmd, *pmd_k;
        pte_t *pte_k;

        pgd = (pgd_t *)per_cpu(current_pgd, smp_processor_id()) + offset;
        pgd_k = init_mm.pgd + offset;

        /* Since we're two-level, we don't need to do both
         * set_pgd and set_pmd (they do the same thing). If
         * we go three-level at some point, do the right thing
         * with pgd_present and set_pgd here.
         *
         * Also, since the vmalloc area is global, we don't
         * need to copy individual PTE's, it is enough to
         * copy the pgd pointer into the pte page of the
         * root task. If that is there, we'll find our pte if
         * it exists.
         */

        pud = pud_offset(pgd, address);
        pud_k = pud_offset(pgd_k, address);
        if (!pud_present(*pud_k))
            goto no_context;

        pmd = pmd_offset(pud, address);
        pmd_k = pmd_offset(pud_k, address);

        if (!pmd_present(*pmd_k))
            goto bad_area_nosemaphore;

        set_pmd(pmd, *pmd_k);

        /* Make sure the actual PTE exists as well to
         * catch kernel vmalloc-area accesses to non-mapped
         * addresses. If we don't do this, this will just
         * silently loop forever.
         */

        pte_k = pte_offset_kernel(pmd_k, address);
        if (!pte_present(*pte_k))
            goto no_context;

        return;
    }
}

/* Find fixup code. */
int
find_fixup_code(struct pt_regs *regs)
{
    const struct exception_table_entry *fixup;
    /* in case of delay slot fault (v32) */
    unsigned long ip = (instruction_pointer(regs) & ~0x1);

    fixup = search_exception_tables(ip);
    if (fixup != 0) {
        /* Adjust the instruction pointer in the stackframe. */
        instruction_pointer(regs) = fixup->fixup;
        arch_fixup(regs);
        return 1;
    }

    return 0;
}