fault.c

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/*
 * MMU fault handling support.
 *
 * Copyright (C) 1998-2002 Hewlett-Packard Co
 *  David Mosberger-Tang <[email protected]>
 */
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/prefetch.h>

#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/uaccess.h>

extern int die(char *, struct pt_regs *, long);

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

    if (!user_mode(regs)) {
        /* kprobe_running() needs smp_processor_id() */
        preempt_disable();
        if (kprobe_running() && kprobe_fault_handler(regs, trap))
            ret = 1;
        preempt_enable();
    }

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

/*
 * Return TRUE if ADDRESS points at a page in the kernel's mapped segment
 * (inside region 5, on ia64) and that page is present.
 */
static int
mapped_kernel_page_is_present (unsigned long address)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *ptep, pte;

    pgd = pgd_offset_k(address);
    if (pgd_none(*pgd) || pgd_bad(*pgd))
        return 0;

    pud = pud_offset(pgd, address);
    if (pud_none(*pud) || pud_bad(*pud))
        return 0;

    pmd = pmd_offset(pud, address);
    if (pmd_none(*pmd) || pmd_bad(*pmd))
        return 0;

    ptep = pte_offset_kernel(pmd, address);
    if (!ptep)
        return 0;

    pte = *ptep;
    return pte_present(pte);
}

#   define VM_READ_BIT  0
#   define VM_WRITE_BIT 1
#   define VM_EXEC_BIT  2

void __kprobes
ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *regs)
{
    int signal = SIGSEGV, code = SEGV_MAPERR;
    struct vm_area_struct *vma, *prev_vma;
    struct mm_struct *mm = current->mm;
    struct siginfo si;
    unsigned long mask;
    int fault;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

    mask = ((((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT)
        | (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT));

    flags |= ((mask & VM_WRITE) ? FAULT_FLAG_WRITE : 0);

    /* mmap_sem is performance critical.... */
    prefetchw(&mm->mmap_sem);

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

#ifdef CONFIG_VIRTUAL_MEM_MAP
    /*
     * If fault is in region 5 and we are in the kernel, we may already
     * have the mmap_sem (pfn_valid macro is called during mmap). There
     * is no vma for region 5 addr's anyway, so skip getting the semaphore
     * and go directly to the exception handling code.
     */

    if ((REGION_NUMBER(address) == 5) && !user_mode(regs))
        goto bad_area_no_up;
#endif

    /*
     * This is to handle the kprobes on user space access instructions
     */
    if (notify_page_fault(regs, TRAP_BRKPT))
        return;

retry:
    down_read(&mm->mmap_sem);

    vma = find_vma_prev(mm, address, &prev_vma);
    if (!vma && !prev_vma )
        goto bad_area;

        /*
         * find_vma_prev() returns vma such that address < vma->vm_end or NULL
         *
         * May find no vma, but could be that the last vm area is the
         * register backing store that needs to expand upwards, in
         * this case vma will be null, but prev_vma will ne non-null
         */
        if (( !vma && prev_vma ) || (address < vma->vm_start) )
        goto check_expansion;

  good_area:
    code = SEGV_ACCERR;

    /* OK, we've got a good vm_area for this memory area.  Check the access permissions: */

#   if (((1 << VM_READ_BIT) != VM_READ || (1 << VM_WRITE_BIT) != VM_WRITE) \
        || (1 << VM_EXEC_BIT) != VM_EXEC)
#       error File is out of sync with <linux/mm.h>.  Please update.
#   endif

    if (((isr >> IA64_ISR_R_BIT) & 1UL) && (!(vma->vm_flags & (VM_READ | VM_WRITE))))
        goto bad_area;

    if ((vma->vm_flags & mask) != mask)
        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)) {
        /*
         * We ran out of memory, or some other thing happened
         * to us that made us unable to handle the page fault
         * gracefully.
         */
        if (fault & VM_FAULT_OOM) {
            goto out_of_memory;
        } else if (fault & VM_FAULT_SIGBUS) {
            signal = SIGBUS;
            goto bad_area;
        }
        BUG();
    }

    if (flags & FAULT_FLAG_ALLOW_RETRY) {
        if (fault & VM_FAULT_MAJOR)
            current->maj_flt++;
        else
            current->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;

  check_expansion:
    if (!(prev_vma && (prev_vma->vm_flags & VM_GROWSUP) && (address == prev_vma->vm_end))) {
        if (!vma)
            goto bad_area;
        if (!(vma->vm_flags & VM_GROWSDOWN))
            goto bad_area;
        if (REGION_NUMBER(address) != REGION_NUMBER(vma->vm_start)
            || REGION_OFFSET(address) >= RGN_MAP_LIMIT)
            goto bad_area;
        if (expand_stack(vma, address))
            goto bad_area;
    } else {
        vma = prev_vma;
        if (REGION_NUMBER(address) != REGION_NUMBER(vma->vm_start)
            || REGION_OFFSET(address) >= RGN_MAP_LIMIT)
            goto bad_area;
        /*
         * Since the register backing store is accessed sequentially,
         * we disallow growing it by more than a page at a time.
         */
        if (address > vma->vm_end + PAGE_SIZE - sizeof(long))
            goto bad_area;
        if (expand_upwards(vma, address))
            goto bad_area;
    }
    goto good_area;

  bad_area:
    up_read(&mm->mmap_sem);
#ifdef CONFIG_VIRTUAL_MEM_MAP
  bad_area_no_up:
#endif
    if ((isr & IA64_ISR_SP)
        || ((isr & IA64_ISR_NA) && (isr & IA64_ISR_CODE_MASK) == IA64_ISR_CODE_LFETCH))
    {
        /*
         * This fault was due to a speculative load or lfetch.fault, set the "ed"
         * bit in the psr to ensure forward progress.  (Target register will get a
         * NaT for ld.s, lfetch will be canceled.)
         */
        ia64_psr(regs)->ed = 1;
        return;
    }
    if (user_mode(regs)) {
        si.si_signo = signal;
        si.si_errno = 0;
        si.si_code = code;
        si.si_addr = (void __user *) address;
        si.si_isr = isr;
        si.si_flags = __ISR_VALID;
        force_sig_info(signal, &si, current);
        return;
    }

  no_context:
    if ((isr & IA64_ISR_SP)
        || ((isr & IA64_ISR_NA) && (isr & IA64_ISR_CODE_MASK) == IA64_ISR_CODE_LFETCH))
    {
        /*
         * This fault was due to a speculative load or lfetch.fault, set the "ed"
         * bit in the psr to ensure forward progress.  (Target register will get a
         * NaT for ld.s, lfetch will be canceled.)
         */
        ia64_psr(regs)->ed = 1;
        return;
    }

    /*
     * Since we have no vma's for region 5, we might get here even if the address is
     * valid, due to the VHPT walker inserting a non present translation that becomes
     * stale. If that happens, the non present fault handler already purged the stale
     * translation, which fixed the problem. So, we check to see if the translation is
     * valid, and return if it is.
     */
    if (REGION_NUMBER(address) == 5 && mapped_kernel_page_is_present(address))
        return;

    if (ia64_done_with_exception(regs))
        return;

    /*
     * Oops. The kernel tried to access some bad page. We'll have to terminate things
     * with extreme prejudice.
     */
    bust_spinlocks(1);

    if (address < PAGE_SIZE)
        printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference (address %016lx)\n", address);
    else
        printk(KERN_ALERT "Unable to handle kernel paging request at "
               "virtual address %016lx\n", address);
    if (die("Oops", regs, isr))
        regs = NULL;
    bust_spinlocks(0);
    if (regs)
        do_exit(SIGKILL);
    return;

  out_of_memory:
    up_read(&mm->mmap_sem);
    if (!user_mode(regs))
        goto no_context;
    pagefault_out_of_memory();
}