/*
   *  arch/microblaze/mm/fault.c
   *
   *    Copyright (C) 2007 Xilinx, Inc.  All rights reserved.
   *
   *  Derived from "arch/ppc/mm/fault.c"
   *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
   *
   *  Derived from "arch/i386/mm/fault.c"
   *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   *
   *  Modified by Cort Dougan and Paul Mackerras.
   *
   * 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.
   *
   */
  
  #include <linux/module.h>
  #include <linux/signal.h>
  #include <linux/sched.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/interrupt.h>
  
  #include <asm/page.h>
  #include <asm/pgtable.h>
  #include <asm/mmu.h>
  #include <linux/mmu_context.h>
  #include <linux/uaccess.h>
  #include <asm/exceptions.h>
  
  static unsigned long pte_misses;	/* updated by do_page_fault() */
  static unsigned long pte_errors;	/* updated by do_page_fault() */
  
  /*
   * Check whether the instruction at regs->pc is a store using
   * an update addressing form which will update r1.
   */
  static int store_updates_sp(struct pt_regs *regs)
  {
  	unsigned int inst;
  
  	if (get_user(inst, (unsigned int __user *)regs->pc))
  		return 0;
  	/* check for 1 in the rD field */
  	if (((inst >> 21) & 0x1f) != 1)
  		return 0;
  	/* check for store opcodes */
  	if ((inst & 0xd0000000) == 0xd0000000)
  		return 1;
  	return 0;
  }
  
  
  /*
   * bad_page_fault is called when we have a bad access from the kernel.
   * It is called from do_page_fault above and from some of the procedures
   * in traps.c.
   */
  void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
  {
  	const struct exception_table_entry *fixup;
  /* MS: no context */
  	/* Are we prepared to handle this fault?  */
  	fixup = search_exception_tables(regs->pc);
  	if (fixup) {
  		regs->pc = fixup->fixup;
  		return;
  	}
  
  	/* kernel has accessed a bad area */
  	die("kernel access of bad area", regs, sig);
  }
  
  /*
   * The error_code parameter is ESR for a data fault,
   * 0 for an instruction fault.
   */
  void do_page_fault(struct pt_regs *regs, unsigned long address,
  		   unsigned long error_code)
  {
  	struct vm_area_struct *vma;
  	struct mm_struct *mm = current->mm;
  	siginfo_t info;
  	int code = SEGV_MAPERR;
  	int is_write = error_code & ESR_S;
  	int fault;
  	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
  
  	regs->ear = address;
  	regs->esr = error_code;
  
  	/* On a kernel SLB miss we can only check for a valid exception entry */
  	if (unlikely(kernel_mode(regs) && (address >= TASK_SIZE))) {
  		pr_warn("kernel task_size exceed");
  		_exception(SIGSEGV, regs, code, address);
  	}
  
  	/* for instr TLB miss and instr storage exception ESR_S is undefined */
  	if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11)
  		is_write = 0;
  
  	if (unlikely(in_atomic() || !mm)) {
  		if (kernel_mode(regs))
  			goto bad_area_nosemaphore;
  
  		/* in_atomic() in user mode is really bad,
  		   as is current->mm == NULL. */
  		pr_emerg("Page fault in user mode with in_atomic(), mm = %p
  ",
  									mm);
  		pr_emerg("r15 = %lx  MSR = %lx
  ",
  		       regs->r15, regs->msr);
  		die("Weird page fault", regs, SIGSEGV);
  	}
  
  	if (user_mode(regs))
  		flags |= FAULT_FLAG_USER;
  
  	/* When running in the kernel we expect faults to occur only to
  	 * addresses in user space.  All other faults represent errors in the
  	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
  	 * erroneous fault occurring in a code path which already holds mmap_sem
  	 * we will deadlock attempting to validate the fault against the
  	 * address space.  Luckily the kernel only validly references user
  	 * space from well defined areas of code, which are listed in the
  	 * exceptions table.
  	 *
  	 * As the vast majority of faults will be valid we will only perform
  	 * the source reference check when there is a possibility of a deadlock.
  	 * Attempt to lock the address space, if we cannot we then validate the
  	 * source.  If this is invalid we can skip the address space check,
  	 * thus avoiding the deadlock.
  	 */
  	if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
  		if (kernel_mode(regs) && !search_exception_tables(regs->pc))
  			goto bad_area_nosemaphore;
  
  retry:
  		down_read(&mm->mmap_sem);
  	}
  
  	vma = find_vma(mm, address);
  	if (unlikely(!vma))
  		goto bad_area;
  
  	if (vma->vm_start <= address)
  		goto good_area;
  
  	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
  		goto bad_area;
  
  	if (unlikely(!is_write))
  		goto bad_area;
  
  	/*
  	 * N.B. The ABI allows programs to access up to
  	 * a few hundred bytes below the stack pointer (TBD).
  	 * The kernel signal delivery code writes up to about 1.5kB
  	 * below the stack pointer (r1) before decrementing it.
  	 * The exec code can write slightly over 640kB to the stack
  	 * before setting the user r1.  Thus we allow the stack to
  	 * expand to 1MB without further checks.
  	 */
  	if (unlikely(address + 0x100000 < vma->vm_end)) {
  
  		/* get user regs even if this fault is in kernel mode */
  		struct pt_regs *uregs = current->thread.regs;
  		if (uregs == NULL)
  			goto bad_area;
  
  		/*
  		 * A user-mode access to an address a long way below
  		 * the stack pointer is only valid if the instruction
  		 * is one which would update the stack pointer to the
  		 * address accessed if the instruction completed,
  		 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
  		 * (or the byte, halfword, float or double forms).
  		 *
  		 * If we don't check this then any write to the area
  		 * between the last mapped region and the stack will
  		 * expand the stack rather than segfaulting.
  		 */
  		if (address + 2048 < uregs->r1
  			&& (kernel_mode(regs) || !store_updates_sp(regs)))
  				goto bad_area;
  	}
  	if (expand_stack(vma, address))
  		goto bad_area;
  
  good_area:
  	code = SEGV_ACCERR;
  
  	/* a write */
  	if (unlikely(is_write)) {
  		if (unlikely(!(vma->vm_flags & VM_WRITE)))
  			goto bad_area;
  		flags |= FAULT_FLAG_WRITE;
  	/* a read */
  	} else {
  		/* protection fault */
  		if (unlikely(error_code & 0x08000000))
  			goto bad_area;
  		if (unlikely(!(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 (unlikely(fault & VM_FAULT_MAJOR))
  			current->maj_flt++;
  		else
  			current->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);
  
  	/*
  	 * keep track of tlb+htab misses that are good addrs but
  	 * just need pte's created via handle_mm_fault()
  	 * -- Cort
  	 */
  	pte_misses++;
  	return;
  
  bad_area:
  	up_read(&mm->mmap_sem);
  
  bad_area_nosemaphore:
  	pte_errors++;
  
  	/* User mode accesses cause a SIGSEGV */
  	if (user_mode(regs)) {
  		_exception(SIGSEGV, regs, code, address);
  /*		info.si_signo = SIGSEGV;
  		info.si_errno = 0;
  		info.si_code = code;
  		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 (!user_mode(regs))
  		bad_page_fault(regs, address, SIGKILL);
  	else
  		pagefault_out_of_memory();
  	return;
  
  do_sigbus:
  	up_read(&mm->mmap_sem);
  	if (user_mode(regs)) {
  		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);
  		return;
  	}
  	bad_page_fault(regs, address, SIGBUS);
  }