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fault.c

/*
 *  linux/arch/alpha/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <asm/io.h>

#define __EXTERN_INLINE inline
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#undef  __EXTERN_INLINE

#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/module.h>

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

extern void die_if_kernel(char *,struct pt_regs *,long, unsigned long *);


/*
 * Force a new ASN for a task.
 */

#ifndef CONFIG_SMP
unsigned long last_asn = ASN_FIRST_VERSION;
#endif

void
__load_new_mm_context(struct mm_struct *next_mm)
{
      unsigned long mmc;
      struct pcb_struct *pcb;

      mmc = __get_new_mm_context(next_mm, smp_processor_id());
      next_mm->context[smp_processor_id()] = mmc;

      pcb = &current_thread_info()->pcb;
      pcb->asn = mmc & HARDWARE_ASN_MASK;
      pcb->ptbr = ((unsigned long) next_mm->pgd - IDENT_ADDR) >> PAGE_SHIFT;

      __reload_thread(pcb);
}


/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to handle_mm_fault().
 *
 * mmcsr:
 *    0 = translation not valid
 *    1 = access violation
 *    2 = fault-on-read
 *    3 = fault-on-execute
 *    4 = fault-on-write
 *
 * cause:
 *    -1 = instruction fetch
 *    0 = load
 *    1 = store
 *
 * Registers $9 through $15 are saved in a block just prior to `regs' and
 * are saved and restored around the call to allow exception code to
 * modify them.
 */

/* Macro for exception fixup code to access integer registers.  */
#define dpf_reg(r)                                          \
      (((unsigned long *)regs)[(r) <= 8 ? (r) : (r) <= 15 ? (r)-16 :    \
                         (r) <= 18 ? (r)+8 : (r)-10])

asmlinkage void
do_page_fault(unsigned long address, unsigned long mmcsr,
            long cause, struct pt_regs *regs)
{
      struct vm_area_struct * vma;
      struct mm_struct *mm = current->mm;
      const struct exception_table_entry *fixup;
      int fault, si_code = SEGV_MAPERR;
      siginfo_t info;

      /* As of EV6, a load into $31/$f31 is a prefetch, and never faults
         (or is suppressed by the PALcode).  Support that for older CPUs
         by ignoring such an instruction.  */
      if (cause == 0) {
            unsigned int insn;
            __get_user(insn, (unsigned int __user *)regs->pc);
            if ((insn >> 21 & 0x1f) == 0x1f &&
                /* ldq ldl ldt lds ldg ldf ldwu ldbu */
                (1ul << (insn >> 26) & 0x30f00001400ul)) {
                  regs->pc += 4;
                  return;
            }
      }

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

#ifdef CONFIG_ALPHA_LARGE_VMALLOC
      if (address >= TASK_SIZE)
            goto vmalloc_fault;
#endif

      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:
      si_code = SEGV_ACCERR;
      if (cause < 0) {
            if (!(vma->vm_flags & VM_EXEC))
                  goto bad_area;
      } else if (!cause) {
            /* Allow reads even for write-only mappings */
            if (!(vma->vm_flags & (VM_READ | VM_WRITE)))
                  goto bad_area;
      } else {
            if (!(vma->vm_flags & VM_WRITE))
                  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, cause > 0 ? FAULT_FLAG_WRITE : 0);
      up_read(&mm->mmap_sem);
      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)
            current->maj_flt++;
      else
            current->min_flt++;
      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))
            goto do_sigsegv;

 no_context:
      /* Are we prepared to handle this fault as an exception?  */
      if ((fixup = search_exception_tables(regs->pc)) != 0) {
            unsigned long newpc;
            newpc = fixup_exception(dpf_reg, fixup, regs->pc);
            regs->pc = newpc;
            return;
      }

      /* Oops. The kernel tried to access some bad page. We'll have to
         terminate things with extreme prejudice.  */
      printk(KERN_ALERT "Unable to handle kernel paging request at "
             "virtual address %016lx\n", address);
      die_if_kernel("Oops", regs, cause, (unsigned long*)regs - 16);
      do_exit(SIGKILL);

      /* 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:
      if (is_global_init(current)) {
            yield();
            down_read(&mm->mmap_sem);
            goto survive;
      }
      printk(KERN_ALERT "VM: killing process %s(%d)\n",
             current->comm, task_pid_nr(current));
      if (!user_mode(regs))
            goto no_context;
      do_group_exit(SIGKILL);

 do_sigbus:
      /* Send a sigbus, regardless of whether we were in kernel
         or user mode.  */
      info.si_signo = SIGBUS;
      info.si_errno = 0;
      info.si_code = BUS_ADRERR;
      info.si_addr = (void __user *) address;
      force_sig_info(SIGBUS, &info, current);
      if (!user_mode(regs))
            goto no_context;
      return;

 do_sigsegv:
      info.si_signo = SIGSEGV;
      info.si_errno = 0;
      info.si_code = si_code;
      info.si_addr = (void __user *) address;
      force_sig_info(SIGSEGV, &info, current);
      return;

#ifdef CONFIG_ALPHA_LARGE_VMALLOC
 vmalloc_fault:
      if (user_mode(regs))
            goto do_sigsegv;
      else {
            /* Synchronize this task's top level page-table
               with the "reference" page table from init.  */
            long index = pgd_index(address);
            pgd_t *pgd, *pgd_k;

            pgd = current->active_mm->pgd + index;
            pgd_k = swapper_pg_dir + index;
            if (!pgd_present(*pgd) && pgd_present(*pgd_k)) {
                  pgd_val(*pgd) = pgd_val(*pgd_k);
                  return;
            }
            goto no_context;
      }
#endif
}

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