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fault.c

/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 1995 - 2000 by Ralf Baechle
 */
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/vt_kern.h>          /* For unblank_screen() */
#include <linux/module.h>

#include <asm/branch.h>
#include <asm/mmu_context.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/ptrace.h>
#include <asm/highmem.h>            /* For VMALLOC_END */

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long write,
                        unsigned long address)
{
      struct vm_area_struct * vma = NULL;
      struct task_struct *tsk = current;
      struct mm_struct *mm = tsk->mm;
      const int field = sizeof(unsigned long) * 2;
      siginfo_t info;
      int fault;

#if 0
      printk("Cpu%d[%s:%d:%0*lx:%ld:%0*lx]\n", raw_smp_processor_id(),
             current->comm, current->pid, field, address, write,
             field, regs->cp0_epc);
#endif

      info.si_code = SEGV_MAPERR;

      /*
       * 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.
       */
      if (unlikely(address >= VMALLOC_START && address <= VMALLOC_END))
            goto vmalloc_fault;
#ifdef MODULE_START
      if (unlikely(address >= MODULE_START && address < MODULE_END))
            goto vmalloc_fault;
#endif

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

      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:
      info.si_code = SEGV_ACCERR;

      if (write) {
            if (!(vma->vm_flags & VM_WRITE))
                  goto bad_area;
      } else {
            if (!(vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)))
                  goto bad_area;
      }

survive:
      /*
       * 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, write);
      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);

bad_area_nosemaphore:
      /* User mode accesses just cause a SIGSEGV */
      if (user_mode(regs)) {
            tsk->thread.cp0_badvaddr = address;
            tsk->thread.error_code = write;
#if 0
            printk("do_page_fault() #2: sending SIGSEGV to %s for "
                   "invalid %s\n%0*lx (epc == %0*lx, ra == %0*lx)\n",
                   tsk->comm,
                   write ? "write access to" : "read access from",
                   field, address,
                   field, (unsigned long) regs->cp0_epc,
                   field, (unsigned long) regs->regs[31]);
#endif
            info.si_signo = SIGSEGV;
            info.si_errno = 0;
            /* info.si_code has been set above */
            info.si_addr = (void __user *) address;
            force_sig_info(SIGSEGV, &info, tsk);
            return;
      }

no_context:
      /* Are we prepared to handle this kernel fault?  */
      if (fixup_exception(regs)) {
            current->thread.cp0_baduaddr = address;
            return;
      }

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

      printk(KERN_ALERT "CPU %d Unable to handle kernel paging request at "
             "virtual address %0*lx, epc == %0*lx, ra == %0*lx\n",
             raw_smp_processor_id(), field, address, field, regs->cp0_epc,
             field,  regs->regs[31]);
      die("Oops", regs);

/*
 * 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(tsk)) {
            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 */
      if (!user_mode(regs))
            goto no_context;
      else
      /*
       * Send a sigbus, regardless of whether we were in kernel
       * or user mode.
       */
#if 0
            printk("do_page_fault() #3: sending SIGBUS to %s for "
                   "invalid %s\n%0*lx (epc == %0*lx, ra == %0*lx)\n",
                   tsk->comm,
                   write ? "write access to" : "read access from",
                   field, address,
                   field, (unsigned long) regs->cp0_epc,
                   field, (unsigned long) regs->regs[31]);
#endif
      tsk->thread.cp0_badvaddr = address;
      info.si_signo = SIGBUS;
      info.si_errno = 0;
      info.si_code = BUS_ADRERR;
      info.si_addr = (void __user *) address;
      force_sig_info(SIGBUS, &info, tsk);

      return;
vmalloc_fault:
      {
            /*
             * Synchronize this task's top level page-table
             * with the 'reference' page table.
             *
             * Do _not_ use "tsk" here. We might be inside
             * an interrupt in the middle of a task switch..
             */
            int offset = __pgd_offset(address);
            pgd_t *pgd, *pgd_k;
            pud_t *pud, *pud_k;
            pmd_t *pmd, *pmd_k;
            pte_t *pte_k;

            pgd = (pgd_t *) pgd_current[raw_smp_processor_id()] + offset;
            pgd_k = init_mm.pgd + offset;

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

            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 no_context;
            set_pmd(pmd, *pmd_k);

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

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