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fault.c

/*
 * 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;
      int writeaccess;
      long signr;
      int code;
      int fault;

      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();

      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;
      writeaccess = 0;

      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;
            writeaccess = 1;
            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.
       */
survive:
      fault = handle_mm_fault(mm, vma, address, writeaccess ? FAULT_FLAG_WRITE : 0);
      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 (fault & VM_FAULT_MAJOR)
            tsk->maj_flt++;
      else
            tsk->min_flt++;

      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);
      if (is_global_init(current)) {
            yield();
            down_read(&mm->mmap_sem);
            goto survive;
      }
      printk("VM: Killing process %s\n", tsk->comm);
      if (user_mode(regs))
            do_group_exit(SIGKILL);
      goto no_context;

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);
}

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