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fault.c

// TODO VM_EXEC flag work-around, cache aliasing
/*
 * arch/xtensa/mm/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) 2001 - 2005 Tensilica Inc.
 *
 * Chris Zankel <chris@zankel.net>
 * Joe Taylor     <joe@tensilica.com, joetylr@yahoo.com>
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <asm/mmu_context.h>
#include <asm/cacheflush.h>
#include <asm/hardirq.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#include <asm/pgalloc.h>

unsigned long asid_cache = ASID_USER_FIRST;
void bad_page_fault(struct pt_regs*, unsigned long, int);

#undef DEBUG_PAGE_FAULT

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * Note: does not handle Miss and MultiHit.
 */

void do_page_fault(struct pt_regs *regs)
{
      struct vm_area_struct * vma;
      struct mm_struct *mm = current->mm;
      unsigned int exccause = regs->exccause;
      unsigned int address = regs->excvaddr;
      siginfo_t info;

      int is_write, is_exec;
      int fault;

      info.si_code = SEGV_MAPERR;

      /* We fault-in kernel-space virtual memory on-demand. The
       * 'reference' page table is init_mm.pgd.
       */
      if (address >= TASK_SIZE && !user_mode(regs))
            goto vmalloc_fault;

      /* If we're in an interrupt or have no user
       * context, we must not take the fault..
       */
      if (in_atomic() || !mm) {
            bad_page_fault(regs, address, SIGSEGV);
            return;
      }

      is_write = (exccause == EXCCAUSE_STORE_CACHE_ATTRIBUTE) ? 1 : 0;
      is_exec =  (exccause == EXCCAUSE_ITLB_PRIVILEGE ||
                exccause == EXCCAUSE_ITLB_MISS ||
                exccause == EXCCAUSE_FETCH_CACHE_ATTRIBUTE) ? 1 : 0;

#ifdef DEBUG_PAGE_FAULT
      printk("[%s:%d:%08x:%d:%08x:%s%s]\n", current->comm, current->pid,
             address, exccause, regs->pc, is_write? "w":"", is_exec? "x":"");
#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:
      info.si_code = SEGV_ACCERR;

      if (is_write) {
            if (!(vma->vm_flags & VM_WRITE))
                  goto bad_area;
      } else if (is_exec) {
            if (!(vma->vm_flags & VM_EXEC))
                  goto bad_area;
      } else      /* Allow read even from write-only pages. */
            if (!(vma->vm_flags & (VM_READ | VM_WRITE)))
                  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.
       */
survive:
      fault = handle_mm_fault(mm, vma, address, is_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)
            current->maj_flt++;
      else
            current->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)) {
            current->thread.bad_vaddr = address;
            current->thread.error_code = is_write;
            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, current);
            return;
      }
      bad_page_fault(regs, address, SIGSEGV);
      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", current->comm);
      if (user_mode(regs))
            do_group_exit(SIGKILL);
      bad_page_fault(regs, address, SIGKILL);
      return;

do_sigbus:
      up_read(&mm->mmap_sem);

      /* Send a sigbus, regardless of whether we were in kernel
       * or user mode.
       */
      current->thread.bad_vaddr = address;
      info.si_code = SIGBUS;
      info.si_errno = 0;
      info.si_code = BUS_ADRERR;
      info.si_addr = (void *) address;
      force_sig_info(SIGBUS, &info, current);

      /* Kernel mode? Handle exceptions or die */
      if (!user_mode(regs))
            bad_page_fault(regs, address, SIGBUS);

vmalloc_fault:
      {
            /* Synchronize this task's top level page-table
             * with the 'reference' page table.
             */
            struct mm_struct *act_mm = current->active_mm;
            int index = pgd_index(address);
            pgd_t *pgd, *pgd_k;
            pmd_t *pmd, *pmd_k;
            pte_t *pte_k;

            if (act_mm == NULL)
                  goto bad_page_fault;

            pgd = act_mm->pgd + index;
            pgd_k = init_mm.pgd + index;

            if (!pgd_present(*pgd_k))
                  goto bad_page_fault;

            pgd_val(*pgd) = pgd_val(*pgd_k);

            pmd = pmd_offset(pgd, address);
            pmd_k = pmd_offset(pgd_k, address);
            if (!pmd_present(*pmd) || !pmd_present(*pmd_k))
                  goto bad_page_fault;

            pmd_val(*pmd) = pmd_val(*pmd_k);
            pte_k = pte_offset_kernel(pmd_k, address);

            if (!pte_present(*pte_k))
                  goto bad_page_fault;
            return;
      }
bad_page_fault:
      bad_page_fault(regs, address, SIGKILL);
      return;
}


void
bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
      extern void die(const char*, struct pt_regs*, long);
      const struct exception_table_entry *entry;

      /* Are we prepared to handle this kernel fault?  */
      if ((entry = search_exception_tables(regs->pc)) != NULL) {
#ifdef DEBUG_PAGE_FAULT
            printk(KERN_DEBUG "%s: Exception at pc=%#010lx (%lx)\n",
                        current->comm, regs->pc, entry->fixup);
#endif
            current->thread.bad_uaddr = address;
            regs->pc = entry->fixup;
            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 %08lx\n pc = %08lx, ra = %08lx\n",
             address, regs->pc, regs->areg[0]);
      die("Oops", regs, sig);
      do_exit(sig);
}


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