/*
   *  arch/cris/mm/fault.c
   *
   *  Copyright (C) 2000-2010  Axis Communications AB
   */
  
  #include <linux/mm.h>
  #include <linux/interrupt.h>
  #include <linux/module.h>
  #include <linux/wait.h>
  #include <asm/uaccess.h>
  #include <arch/system.h>
  
  extern int find_fixup_code(struct pt_regs *);
  extern void die_if_kernel(const char *, struct pt_regs *, long);
  extern void show_registers(struct pt_regs *regs);
  
  /* 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 */
  
  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;
  	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
  
  	D(printk(KERN_DEBUG
  		 "Page fault for %lX on %X at %lX, prot %d write %d
  ",
  		 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 "atomic" operation or have no
  	 * user context, we must not take the fault.
  	 */
  
  	if (in_atomic() || !mm)
  		goto no_context;
  
  	if (user_mode(regs))
  		flags |= FAULT_FLAG_USER;
  retry:
  	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;
  		flags |= FAULT_FLAG_WRITE;
  	} 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, flags);
  
  	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
  		return;
  
  	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 (flags & FAULT_FLAG_ALLOW_RETRY) {
  		if (fault & VM_FAULT_MAJOR)
  			tsk->maj_flt++;
  		else
  			tsk->min_flt++;
  		if (fault & VM_FAULT_RETRY) {
  			flags &= ~FAULT_FLAG_ALLOW_RETRY;
  			flags |= FAULT_FLAG_TRIED;
  
  			/*
  			 * No need to up_read(&mm->mmap_sem) as we would
  			 * have already released it in __lock_page_or_retry
  			 * in mm/filemap.c.
  			 */
  
  			goto retry;
  		}
  	}
  
  	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)) {
  		printk(KERN_NOTICE "%s (pid %d) segfaults for page "
  			"address %08lx at pc %08lx
  ",
  			tsk->comm, tsk->pid,
  			address, instruction_pointer(regs));
  
  		/* With DPG on, we've already dumped registers above.  */
  		DPG(if (0))
  			show_registers(regs);
  
  #ifdef CONFIG_NO_SEGFAULT_TERMINATION
  		DECLARE_WAIT_QUEUE_HEAD(wq);
  		wait_event_interruptible(wq, 0 == 1);
  #else
  		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);
  #endif
  		return;
  	}
  
   no_context:
  
  	/* Are we prepared to handle this kernel fault?
  	 *
  	 * (The kernel has valid exception-points in the source
  	 *  when it accesses 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
  ", 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);
  	if (!user_mode(regs))
  		goto no_context;
  	pagefault_out_of_memory();
  	return;
  
   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;
  	/* in case of delay slot fault (v32) */
  	unsigned long ip = (instruction_pointer(regs) & ~0x1);
  
  	fixup = search_exception_tables(ip);
  	if (fixup != 0) {
  		/* Adjust the instruction pointer in the stackframe. */
  		instruction_pointer(regs) = fixup->fixup;
  		arch_fixup(regs);
  		return 1;
  	}
  
  	return 0;
  }