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fault.c

/*
 * MMU fault handling support.
 *
 * Copyright (C) 1998-2002 Hewlett-Packard Co
 *    David Mosberger-Tang <davidm@hpl.hp.com>
 */
#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 <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/system.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);
}

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;

      /* 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;

      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: */

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

#     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;

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

      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, (mask & VM_WRITE) ? FAULT_FLAG_WRITE : 0);
      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 (fault & VM_FAULT_MAJOR)
            current->maj_flt++;
      else
            current->min_flt++;
      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();
}

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