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fault.c

/*
 *  linux/arch/cris/mm/fault.c
 *
 *  Copyright (C) 2000-2006  Axis Communications AB
 *
 *  Authors:  Bjorn Wesen
 *
 */

#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <asm/uaccess.h>

extern int find_fixup_code(struct pt_regs *);
extern void die_if_kernel(const char *, struct pt_regs *, long);

/* debug of low-level TLB reload */
#undef DEBUG

#ifdef DEBUG
#define D(x) x
#else
#define D(x)
#endif

/* debug of higher-level faults */
#define DPG(x)

/* current active page directory */

volatile DEFINE_PER_CPU(pgd_t *,current_pgd);
unsigned long cris_signal_return_page;

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * Notice that the address we're given is aligned to the page the fault
 * occurred in, since we only get the PFN in R_MMU_CAUSE not the complete
 * address.
 *
 * error_code:
 *      bit 0 == 0 means no page found, 1 means protection fault
 *      bit 1 == 0 means read, 1 means write
 *
 * If this routine detects a bad access, it returns 1, otherwise it
 * returns 0.
 */

asmlinkage void
do_page_fault(unsigned long address, struct pt_regs *regs,
            int protection, int writeaccess)
{
      struct task_struct *tsk;
      struct mm_struct *mm;
      struct vm_area_struct * vma;
      siginfo_t info;
      int fault;

      D(printk(KERN_DEBUG
             "Page fault for %lX on %X at %lX, prot %d write %d\n",
             address, smp_processor_id(), instruction_pointer(regs),
             protection, writeaccess));

      tsk = current;

      /*
       * 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.
       *
       * NOTE2: This is done so that, when updating the vmalloc
       * mappings we don't have to walk all processes pgdirs and
       * add the high mappings all at once. Instead we do it as they
       * are used. However vmalloc'ed page entries have the PAGE_GLOBAL
       * bit set so sometimes the TLB can use a lingering entry.
       *
       * This verifies that the fault happens in kernel space
       * and that the fault was not a protection error (error_code & 1).
       */

      if (address >= VMALLOC_START &&
          !protection &&
          !user_mode(regs))
            goto vmalloc_fault;

      /* When stack execution is not allowed we store the signal
       * trampolines in the reserved cris_signal_return_page.
       * Handle this in the exact same way as vmalloc (we know
       * that the mapping is there and is valid so no need to
       * call handle_mm_fault).
       */
      if (cris_signal_return_page &&
          address == cris_signal_return_page &&
          !protection && user_mode(regs))
            goto vmalloc_fault;

      /* we can and should enable interrupts at this point */
      local_irq_enable();

      mm = tsk->mm;
      info.si_code = SEGV_MAPERR;

      /*
       * If we're in an interrupt or have no user
       * context, we must not take the fault..
       */

      if (in_interrupt() || !mm)
            goto no_context;

      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 (user_mode(regs)) {
            /*
             * accessing the stack below usp is always a bug.
             * we get page-aligned addresses so we can only check
             * if we're within a page from usp, but that might be
             * enough to catch brutal errors at least.
             */
            if (address + PAGE_SIZE < rdusp())
                  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;

      /* first do some preliminary protection checks */

      if (writeaccess == 2){
            if (!(vma->vm_flags & VM_EXEC))
                  goto bad_area;
      } else if (writeaccess == 1) {
            if (!(vma->vm_flags & VM_WRITE))
                  goto bad_area;
      } else {
            if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
                  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, writeaccess & 1);
      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:
      DPG(show_registers(regs));

      /* User mode accesses just cause a SIGSEGV */

      if (user_mode(regs)) {
            info.si_signo = SIGSEGV;
            info.si_errno = 0;
            /* info.si_code has been set above */
            info.si_addr = (void *)address;
            force_sig_info(SIGSEGV, &info, tsk);
            printk(KERN_NOTICE "%s (pid %d) segfaults for page "
                   "address %08lx at pc %08lx\n",
                   tsk->comm, tsk->pid, address, instruction_pointer(regs));
            return;
      }

 no_context:

      /* Are we prepared to handle this kernel fault?
       *
       * (The kernel has valid exception-points in the source
       *  when it acesses user-memory. When it fails in one
       *  of those points, we find it in a table and do a jump
       *  to some fixup code that loads an appropriate error
       *  code)
       */

      if (find_fixup_code(regs))
            return;

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

      if (!oops_in_progress) {
            oops_in_progress = 1;
            if ((unsigned long) (address) < PAGE_SIZE)
                  printk(KERN_ALERT "Unable to handle kernel NULL "
                        "pointer dereference");
            else
                  printk(KERN_ALERT "Unable to handle kernel access"
                        " at virtual address %08lx\n", address);

            die_if_kernel("Oops", regs, (writeaccess << 1) | protection);
            oops_in_progress = 0;
      }

      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:
      up_read(&mm->mmap_sem);
      printk("VM: killing process %s\n", tsk->comm);
      if (user_mode(regs))
            do_exit(SIGKILL);
      goto no_context;

 do_sigbus:
      up_read(&mm->mmap_sem);

      /*
       * 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 *)address;
      force_sig_info(SIGBUS, &info, tsk);

      /* Kernel mode? Handle exceptions or die */
      if (!user_mode(regs))
            goto no_context;
      return;

vmalloc_fault:
      {
            /*
             * Synchronize this task's top level page-table
             * with the 'reference' page table.
             *
             * Use current_pgd instead of tsk->active_mm->pgd
             * since the latter might be unavailable if this
             * code is executed in a misfortunately run irq
             * (like inside schedule() between switch_mm and
             *  switch_to...).
             */

            int offset = pgd_index(address);
            pgd_t *pgd, *pgd_k;
            pud_t *pud, *pud_k;
            pmd_t *pmd, *pmd_k;
            pte_t *pte_k;

            pgd = (pgd_t *)per_cpu(current_pgd, smp_processor_id()) + offset;
            pgd_k = init_mm.pgd + offset;

            /* Since we're two-level, we don't need to do both
             * set_pgd and set_pmd (they do the same thing). If
             * we go three-level at some point, do the right thing
             * with pgd_present and set_pgd here.
             *
             * Also, since the vmalloc area is global, we don't
             * need to copy individual PTE's, it is enough to
             * copy the pgd pointer into the pte page of the
             * root task. If that is there, we'll find our pte if
             * it exists.
             */

            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 bad_area_nosemaphore;

            set_pmd(pmd, *pmd_k);

            /* Make sure the actual PTE exists as well to
             * catch kernel vmalloc-area accesses to non-mapped
             * addresses. If we don't do this, this will just
             * silently loop forever.
             */

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

            return;
      }
}

/* Find fixup code. */
int
find_fixup_code(struct pt_regs *regs)
{
      const struct exception_table_entry *fixup;

      if ((fixup = search_exception_tables(instruction_pointer(regs))) != 0) {
            /* Adjust the instruction pointer in the stackframe. */
            instruction_pointer(regs) = fixup->fixup;
            arch_fixup(regs);
            return 1;
      }

      return 0;
}

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