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fault.c

/*
 *  linux/arch/arm/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 *  Modifications for ARM processor (c) 1995-2004 Russell King
 *
 * 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/module.h>
#include <linux/signal.h>
#include <linux/mm.h>
#include <linux/init.h>

#include <asm/system.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/uaccess.h>

#include "fault.h"

/*
 * This is useful to dump out the page tables associated with
 * 'addr' in mm 'mm'.
 */
void show_pte(struct mm_struct *mm, unsigned long addr)
{
      pgd_t *pgd;

      if (!mm)
            mm = &init_mm;

      printk(KERN_ALERT "pgd = %p\n", mm->pgd);
      pgd = pgd_offset(mm, addr);
      printk(KERN_ALERT "[%08lx] *pgd=%08lx", addr, pgd_val(*pgd));

      do {
            pmd_t *pmd;
            pte_t *pte;

            if (pgd_none(*pgd))
                  break;

            if (pgd_bad(*pgd)) {
                  printk("(bad)");
                  break;
            }

            pmd = pmd_offset(pgd, addr);
#if PTRS_PER_PMD != 1
            printk(", *pmd=%08lx", pmd_val(*pmd));
#endif

            if (pmd_none(*pmd))
                  break;

            if (pmd_bad(*pmd)) {
                  printk("(bad)");
                  break;
            }

#ifndef CONFIG_HIGHMEM
            /* We must not map this if we have highmem enabled */
            pte = pte_offset_map(pmd, addr);
            printk(", *pte=%08lx", pte_val(*pte));
            printk(", *ppte=%08lx", pte_val(pte[-PTRS_PER_PTE]));
            pte_unmap(pte);
#endif
      } while(0);

      printk("\n");
}

/*
 * Oops.  The kernel tried to access some page that wasn't present.
 */
static void
__do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
              struct pt_regs *regs)
{
      /*
       * Are we prepared to handle this kernel fault?
       */
      if (fixup_exception(regs))
            return;

      /*
       * No handler, we'll have to terminate things with extreme prejudice.
       */
      bust_spinlocks(1);
      printk(KERN_ALERT
            "Unable to handle kernel %s at virtual address %08lx\n",
            (addr < PAGE_SIZE) ? "NULL pointer dereference" :
            "paging request", addr);

      show_pte(mm, addr);
      die("Oops", regs, fsr);
      bust_spinlocks(0);
      do_exit(SIGKILL);
}

/*
 * Something tried to access memory that isn't in our memory map..
 * User mode accesses just cause a SIGSEGV
 */
static void
__do_user_fault(struct task_struct *tsk, unsigned long addr,
            unsigned int fsr, unsigned int sig, int code,
            struct pt_regs *regs)
{
      struct siginfo si;

#ifdef CONFIG_DEBUG_USER
      if (user_debug & UDBG_SEGV) {
            printk(KERN_DEBUG "%s: unhandled page fault (%d) at 0x%08lx, code 0x%03x\n",
                   tsk->comm, sig, addr, fsr);
            show_pte(tsk->mm, addr);
            show_regs(regs);
      }
#endif

      tsk->thread.address = addr;
      tsk->thread.error_code = fsr;
      tsk->thread.trap_no = 14;
      si.si_signo = sig;
      si.si_errno = 0;
      si.si_code = code;
      si.si_addr = (void __user *)addr;
      force_sig_info(sig, &si, tsk);
}

void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
      struct task_struct *tsk = current;
      struct mm_struct *mm = tsk->active_mm;

      /*
       * If we are in kernel mode at this point, we
       * have no context to handle this fault with.
       */
      if (user_mode(regs))
            __do_user_fault(tsk, addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
      else
            __do_kernel_fault(mm, addr, fsr, regs);
}

#define VM_FAULT_BADMAP       0x010000
#define VM_FAULT_BADACCESS    0x020000

static int
__do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
            struct task_struct *tsk)
{
      struct vm_area_struct *vma;
      int fault, mask;

      vma = find_vma(mm, addr);
      fault = VM_FAULT_BADMAP;
      if (!vma)
            goto out;
      if (vma->vm_start > addr)
            goto check_stack;

      /*
       * Ok, we have a good vm_area for this
       * memory access, so we can handle it.
       */
good_area:
      if (fsr & (1 << 11)) /* write? */
            mask = VM_WRITE;
      else
            mask = VM_READ|VM_EXEC|VM_WRITE;

      fault = VM_FAULT_BADACCESS;
      if (!(vma->vm_flags & mask))
            goto out;

      /*
       * 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, addr & PAGE_MASK, fsr & (1 << 11));
      if (unlikely(fault & VM_FAULT_ERROR)) {
            if (fault & VM_FAULT_OOM)
                  goto out_of_memory;
            else if (fault & VM_FAULT_SIGBUS)
                  return fault;
            BUG();
      }
      if (fault & VM_FAULT_MAJOR)
            tsk->maj_flt++;
      else
            tsk->min_flt++;
      return fault;

out_of_memory:
      if (!is_global_init(tsk))
            goto out;

      /*
       * If we are out of memory for pid1, sleep for a while and retry
       */
      up_read(&mm->mmap_sem);
      yield();
      down_read(&mm->mmap_sem);
      goto survive;

check_stack:
      if (vma->vm_flags & VM_GROWSDOWN && !expand_stack(vma, addr))
            goto good_area;
out:
      return fault;
}

static int
do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
      struct task_struct *tsk;
      struct mm_struct *mm;
      int fault, sig, code;

      tsk = current;
      mm  = tsk->mm;

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

      /*
       * As per x86, we may deadlock here.  However, since the kernel only
       * validly references user space from well defined areas of the code,
       * we can bug out early if this is from code which shouldn't.
       */
      if (!down_read_trylock(&mm->mmap_sem)) {
            if (!user_mode(regs) && !search_exception_tables(regs->ARM_pc))
                  goto no_context;
            down_read(&mm->mmap_sem);
      }

      fault = __do_page_fault(mm, addr, fsr, tsk);
      up_read(&mm->mmap_sem);

      /*
       * Handle the "normal" case first - VM_FAULT_MAJOR / VM_FAULT_MINOR
       */
      if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP | VM_FAULT_BADACCESS))))
            return 0;

      /*
       * If we are in kernel mode at this point, we
       * have no context to handle this fault with.
       */
      if (!user_mode(regs))
            goto no_context;

      if (fault & VM_FAULT_OOM) {
            /*
             * We ran out of memory, or some other thing
             * happened to us that made us unable to handle
             * the page fault gracefully.
             */
            printk("VM: killing process %s\n", tsk->comm);
            do_group_exit(SIGKILL);
            return 0;
      }
      if (fault & VM_FAULT_SIGBUS) {
            /*
             * We had some memory, but were unable to
             * successfully fix up this page fault.
             */
            sig = SIGBUS;
            code = BUS_ADRERR;
      } else {
            /*
             * Something tried to access memory that
             * isn't in our memory map..
             */
            sig = SIGSEGV;
            code = fault == VM_FAULT_BADACCESS ?
                  SEGV_ACCERR : SEGV_MAPERR;
      }

      __do_user_fault(tsk, addr, fsr, sig, code, regs);
      return 0;

no_context:
      __do_kernel_fault(mm, addr, fsr, regs);
      return 0;
}

/*
 * First Level Translation Fault Handler
 *
 * We enter here because the first level page table doesn't contain
 * a valid entry for the address.
 *
 * If the address is in kernel space (>= TASK_SIZE), then we are
 * probably faulting in the vmalloc() area.
 *
 * If the init_task's first level page tables contains the relevant
 * entry, we copy the it to this task.  If not, we send the process
 * a signal, fixup the exception, or oops the kernel.
 *
 * 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.
 */
static int
do_translation_fault(unsigned long addr, unsigned int fsr,
                 struct pt_regs *regs)
{
      unsigned int index;
      pgd_t *pgd, *pgd_k;
      pmd_t *pmd, *pmd_k;

      if (addr < TASK_SIZE)
            return do_page_fault(addr, fsr, regs);

      index = pgd_index(addr);

      /*
       * FIXME: CP15 C1 is write only on ARMv3 architectures.
       */
      pgd = cpu_get_pgd() + index;
      pgd_k = init_mm.pgd + index;

      if (pgd_none(*pgd_k))
            goto bad_area;

      if (!pgd_present(*pgd))
            set_pgd(pgd, *pgd_k);

      pmd_k = pmd_offset(pgd_k, addr);
      pmd   = pmd_offset(pgd, addr);

      if (pmd_none(*pmd_k))
            goto bad_area;

      copy_pmd(pmd, pmd_k);
      return 0;

bad_area:
      do_bad_area(addr, fsr, regs);
      return 0;
}

/*
 * Some section permission faults need to be handled gracefully.
 * They can happen due to a __{get,put}_user during an oops.
 */
static int
do_sect_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
      do_bad_area(addr, fsr, regs);
      return 0;
}

/*
 * This abort handler always returns "fault".
 */
static int
do_bad(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
      return 1;
}

static struct fsr_info {
      int   (*fn)(unsigned long addr, unsigned int fsr, struct pt_regs *regs);
      int   sig;
      int   code;
      const char *name;
} fsr_info[] = {
      /*
       * The following are the standard ARMv3 and ARMv4 aborts.  ARMv5
       * defines these to be "precise" aborts.
       */
      { do_bad,         SIGSEGV, 0,       "vector exception"               },
      { do_bad,         SIGILL,      BUS_ADRALN,      "alignment exception"            },
      { do_bad,         SIGKILL, 0,       "terminal exception"             },
      { do_bad,         SIGILL,      BUS_ADRALN,      "alignment exception"            },
      { do_bad,         SIGBUS,      0,         "external abort on linefetch"    },
      { do_translation_fault, SIGSEGV, SEGV_MAPERR,   "section translation fault"      },
      { do_bad,         SIGBUS,      0,         "external abort on linefetch"    },
      { do_page_fault,  SIGSEGV, SEGV_MAPERR,   "page translation fault"         },
      { do_bad,         SIGBUS,      0,         "external abort on non-linefetch"  },
      { do_bad,         SIGSEGV, SEGV_ACCERR,   "section domain fault"           },
      { do_bad,         SIGBUS,      0,         "external abort on non-linefetch"  },
      { do_bad,         SIGSEGV, SEGV_ACCERR,   "page domain fault"              },
      { do_bad,         SIGBUS,      0,         "external abort on translation"        },
      { do_sect_fault,  SIGSEGV, SEGV_ACCERR,   "section permission fault"       },
      { do_bad,         SIGBUS,      0,         "external abort on translation"        },
      { do_page_fault,  SIGSEGV, SEGV_ACCERR,   "page permission fault"          },
      /*
       * The following are "imprecise" aborts, which are signalled by bit
       * 10 of the FSR, and may not be recoverable.  These are only
       * supported if the CPU abort handler supports bit 10.
       */
      { do_bad,         SIGBUS,  0,       "unknown 16"                     },
      { do_bad,         SIGBUS,  0,       "unknown 17"                     },
      { do_bad,         SIGBUS,  0,       "unknown 18"                     },
      { do_bad,         SIGBUS,  0,       "unknown 19"                     },
      { do_bad,         SIGBUS,  0,       "lock abort"                     }, /* xscale */
      { do_bad,         SIGBUS,  0,       "unknown 21"                     },
      { do_bad,         SIGBUS,  BUS_OBJERR,    "imprecise external abort"       }, /* xscale */
      { do_bad,         SIGBUS,  0,       "unknown 23"                     },
      { do_bad,         SIGBUS,  0,       "dcache parity error"            }, /* xscale */
      { do_bad,         SIGBUS,  0,       "unknown 25"                     },
      { do_bad,         SIGBUS,  0,       "unknown 26"                     },
      { do_bad,         SIGBUS,  0,       "unknown 27"                     },
      { do_bad,         SIGBUS,  0,       "unknown 28"                     },
      { do_bad,         SIGBUS,  0,       "unknown 29"                     },
      { do_bad,         SIGBUS,  0,       "unknown 30"                     },
      { do_bad,         SIGBUS,  0,       "unknown 31"                     }
};

void __init
hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *),
            int sig, const char *name)
{
      if (nr >= 0 && nr < ARRAY_SIZE(fsr_info)) {
            fsr_info[nr].fn   = fn;
            fsr_info[nr].sig  = sig;
            fsr_info[nr].name = name;
      }
}

/*
 * Dispatch a data abort to the relevant handler.
 */
asmlinkage void __exception
do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
      const struct fsr_info *inf = fsr_info + (fsr & 15) + ((fsr & (1 << 10)) >> 6);
      struct siginfo info;

      if (!inf->fn(addr, fsr, regs))
            return;

      printk(KERN_ALERT "Unhandled fault: %s (0x%03x) at 0x%08lx\n",
            inf->name, fsr, addr);

      info.si_signo = inf->sig;
      info.si_errno = 0;
      info.si_code  = inf->code;
      info.si_addr  = (void __user *)addr;
      arm_notify_die("", regs, &info, fsr, 0);
}

asmlinkage void __exception
do_PrefetchAbort(unsigned long addr, struct pt_regs *regs)
{
      do_translation_fault(addr, 0, regs);
}


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