/*
   * Page fault handler for SH with an MMU.
   *
   *  Copyright (C) 1999  Niibe Yutaka
   *  Copyright (C) 2003 - 2012  Paul Mundt
   *
   *  Based on linux/arch/i386/mm/fault.c:
   *   Copyright (C) 1995  Linus Torvalds
   *
   * 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/kernel.h>
  #include <linux/mm.h>
  #include <linux/hardirq.h>
  #include <linux/kprobes.h>
  #include <linux/perf_event.h>
  #include <linux/kdebug.h>
  #include <asm/io_trapped.h>
  #include <asm/mmu_context.h>
  #include <asm/tlbflush.h>
  #include <asm/traps.h>
  
  static inline int notify_page_fault(struct pt_regs *regs, int trap)
  {
  	int ret = 0;
  
  	if (kprobes_built_in() && !user_mode(regs)) {
  		preempt_disable();
  		if (kprobe_running() && kprobe_fault_handler(regs, trap))
  			ret = 1;
  		preempt_enable();
  	}
  
  	return ret;
  }
  
  static void
  force_sig_info_fault(int si_signo, int si_code, unsigned long address,
  		     struct task_struct *tsk)
  {
  	siginfo_t info;
  
  	info.si_signo	= si_signo;
  	info.si_errno	= 0;
  	info.si_code	= si_code;
  	info.si_addr	= (void __user *)address;
  
  	force_sig_info(si_signo, &info, tsk);
  }
  
  /*
   * This is useful to dump out the page tables associated with
   * 'addr' in mm 'mm'.
   */
  static void show_pte(struct mm_struct *mm, unsigned long addr)
  {
  	pgd_t *pgd;
  
  	if (mm) {
  		pgd = mm->pgd;
  	} else {
  		pgd = get_TTB();
  
  		if (unlikely(!pgd))
  			pgd = swapper_pg_dir;
  	}
  
  	printk(KERN_ALERT "pgd = %p
  ", pgd);
  	pgd += pgd_index(addr);
  	printk(KERN_ALERT "[%08lx] *pgd=%0*Lx", addr,
  	       (u32)(sizeof(*pgd) * 2), (u64)pgd_val(*pgd));
  
  	do {
  		pud_t *pud;
  		pmd_t *pmd;
  		pte_t *pte;
  
  		if (pgd_none(*pgd))
  			break;
  
  		if (pgd_bad(*pgd)) {
  			printk("(bad)");
  			break;
  		}
  
  		pud = pud_offset(pgd, addr);
  		if (PTRS_PER_PUD != 1)
  			printk(", *pud=%0*Lx", (u32)(sizeof(*pud) * 2),
  			       (u64)pud_val(*pud));
  
  		if (pud_none(*pud))
  			break;
  
  		if (pud_bad(*pud)) {
  			printk("(bad)");
  			break;
  		}
  
  		pmd = pmd_offset(pud, addr);
  		if (PTRS_PER_PMD != 1)
  			printk(", *pmd=%0*Lx", (u32)(sizeof(*pmd) * 2),
  			       (u64)pmd_val(*pmd));
  
  		if (pmd_none(*pmd))
  			break;
  
  		if (pmd_bad(*pmd)) {
  			printk("(bad)");
  			break;
  		}
  
  		/* We must not map this if we have highmem enabled */
  		if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
  			break;
  
  		pte = pte_offset_kernel(pmd, addr);
  		printk(", *pte=%0*Lx", (u32)(sizeof(*pte) * 2),
  		       (u64)pte_val(*pte));
  	} while (0);
  
  	printk("
  ");
  }
  
  static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
  {
  	unsigned index = pgd_index(address);
  	pgd_t *pgd_k;
  	pud_t *pud, *pud_k;
  	pmd_t *pmd, *pmd_k;
  
  	pgd += index;
  	pgd_k = init_mm.pgd + index;
  
  	if (!pgd_present(*pgd_k))
  		return NULL;
  
  	pud = pud_offset(pgd, address);
  	pud_k = pud_offset(pgd_k, address);
  	if (!pud_present(*pud_k))
  		return NULL;
  
  	if (!pud_present(*pud))
  	    set_pud(pud, *pud_k);
  
  	pmd = pmd_offset(pud, address);
  	pmd_k = pmd_offset(pud_k, address);
  	if (!pmd_present(*pmd_k))
  		return NULL;
  
  	if (!pmd_present(*pmd))
  		set_pmd(pmd, *pmd_k);
  	else {
  		/*
  		 * The page tables are fully synchronised so there must
  		 * be another reason for the fault. Return NULL here to
  		 * signal that we have not taken care of the fault.
  		 */
  		BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
  		return NULL;
  	}
  
  	return pmd_k;
  }
  
  #ifdef CONFIG_SH_STORE_QUEUES
  #define __FAULT_ADDR_LIMIT	P3_ADDR_MAX
  #else
  #define __FAULT_ADDR_LIMIT	VMALLOC_END
  #endif
  
  /*
   * Handle a fault on the vmalloc or module mapping area
   */
  static noinline int vmalloc_fault(unsigned long address)
  {
  	pgd_t *pgd_k;
  	pmd_t *pmd_k;
  	pte_t *pte_k;
  
  	/* Make sure we are in vmalloc/module/P3 area: */
  	if (!(address >= VMALLOC_START && address < __FAULT_ADDR_LIMIT))
  		return -1;
  
  	/*
  	 * Synchronize this task's top level page-table
  	 * with the 'reference' page table.
  	 *
  	 * Do _not_ use "current" here. We might be inside
  	 * an interrupt in the middle of a task switch..
  	 */
  	pgd_k = get_TTB();
  	pmd_k = vmalloc_sync_one(pgd_k, address);
  	if (!pmd_k)
  		return -1;
  
  	pte_k = pte_offset_kernel(pmd_k, address);
  	if (!pte_present(*pte_k))
  		return -1;
  
  	return 0;
  }
  
  static void
  show_fault_oops(struct pt_regs *regs, unsigned long address)
  {
  	if (!oops_may_print())
  		return;
  
  	printk(KERN_ALERT "BUG: unable to handle kernel ");
  	if (address < PAGE_SIZE)
  		printk(KERN_CONT "NULL pointer dereference");
  	else
  		printk(KERN_CONT "paging request");
  
  	printk(KERN_CONT " at %08lx
  ", address);
  	printk(KERN_ALERT "PC:");
  	printk_address(regs->pc, 1);
  
  	show_pte(NULL, address);
  }
  
  static noinline void
  no_context(struct pt_regs *regs, unsigned long error_code,
  	   unsigned long address)
  {
  	/* Are we prepared to handle this kernel fault?  */
  	if (fixup_exception(regs))
  		return;
  
  	if (handle_trapped_io(regs, address))
  		return;
  
  	/*
  	 * Oops. The kernel tried to access some bad page. We'll have to
  	 * terminate things with extreme prejudice.
  	 */
  	bust_spinlocks(1);
  
  	show_fault_oops(regs, address);
  
  	die("Oops", regs, error_code);
  	bust_spinlocks(0);
  	do_exit(SIGKILL);
  }
  
  static void
  __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
  		       unsigned long address, int si_code)
  {
  	struct task_struct *tsk = current;
  
  	/* User mode accesses just cause a SIGSEGV */
  	if (user_mode(regs)) {
  		/*
  		 * It's possible to have interrupts off here:
  		 */
  		local_irq_enable();
  
  		force_sig_info_fault(SIGSEGV, si_code, address, tsk);
  
  		return;
  	}
  
  	no_context(regs, error_code, address);
  }
  
  static noinline void
  bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
  		     unsigned long address)
  {
  	__bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR);
  }
  
  static void
  __bad_area(struct pt_regs *regs, unsigned long error_code,
  	   unsigned long address, int si_code)
  {
  	struct mm_struct *mm = current->mm;
  
  	/*
  	 * Something tried to access memory that isn't in our memory map..
  	 * Fix it, but check if it's kernel or user first..
  	 */
  	up_read(&mm->mmap_sem);
  
  	__bad_area_nosemaphore(regs, error_code, address, si_code);
  }
  
  static noinline void
  bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
  {
  	__bad_area(regs, error_code, address, SEGV_MAPERR);
  }
  
  static noinline void
  bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
  		      unsigned long address)
  {
  	__bad_area(regs, error_code, address, SEGV_ACCERR);
  }
  
  static void
  do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address)
  {
  	struct task_struct *tsk = current;
  	struct mm_struct *mm = tsk->mm;
  
  	up_read(&mm->mmap_sem);
  
  	/* Kernel mode? Handle exceptions or die: */
  	if (!user_mode(regs))
  		no_context(regs, error_code, address);
  
  	force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
  }
  
  static noinline int
  mm_fault_error(struct pt_regs *regs, unsigned long error_code,
  	       unsigned long address, unsigned int fault)
  {
  	/*
  	 * Pagefault was interrupted by SIGKILL. We have no reason to
  	 * continue pagefault.
  	 */
  	if (fatal_signal_pending(current)) {
  		if (!(fault & VM_FAULT_RETRY))
  			up_read(&current->mm->mmap_sem);
  		if (!user_mode(regs))
  			no_context(regs, error_code, address);
  		return 1;
  	}
  
  	if (!(fault & VM_FAULT_ERROR))
  		return 0;
  
  	if (fault & VM_FAULT_OOM) {
  		/* Kernel mode? Handle exceptions or die: */
  		if (!user_mode(regs)) {
  			up_read(&current->mm->mmap_sem);
  			no_context(regs, error_code, address);
  			return 1;
  		}
  		up_read(&current->mm->mmap_sem);
  
  		/*
  		 * We ran out of memory, call the OOM killer, and return the
  		 * userspace (which will retry the fault, or kill us if we got
  		 * oom-killed):
  		 */
  		pagefault_out_of_memory();
  	} else {
  		if (fault & VM_FAULT_SIGBUS)
  			do_sigbus(regs, error_code, address);
  		else
  			BUG();
  	}
  
  	return 1;
  }
  
  static inline int access_error(int error_code, struct vm_area_struct *vma)
  {
  	if (error_code & FAULT_CODE_WRITE) {
  		/* write, present and write, not present: */
  		if (unlikely(!(vma->vm_flags & VM_WRITE)))
  			return 1;
  		return 0;
  	}
  
  	/* ITLB miss on NX page */
  	if (unlikely((error_code & FAULT_CODE_ITLB) &&
  		     !(vma->vm_flags & VM_EXEC)))
  		return 1;
  
  	/* read, not present: */
  	if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
  		return 1;
  
  	return 0;
  }
  
  static int fault_in_kernel_space(unsigned long address)
  {
  	return address >= TASK_SIZE;
  }
  
  /*
   * This routine handles page faults.  It determines the address,
   * and the problem, and then passes it off to one of the appropriate
   * routines.
   */
  asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
  					unsigned long error_code,
  					unsigned long address)
  {
  	unsigned long vec;
  	struct task_struct *tsk;
  	struct mm_struct *mm;
  	struct vm_area_struct * vma;
  	int fault;
  	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
  
  	tsk = current;
  	mm = tsk->mm;
  	vec = lookup_exception_vector();
  
  	/*
  	 * 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.
  	 */
  	if (unlikely(fault_in_kernel_space(address))) {
  		if (vmalloc_fault(address) >= 0)
  			return;
  		if (notify_page_fault(regs, vec))
  			return;
  
  		bad_area_nosemaphore(regs, error_code, address);
  		return;
  	}
  
  	if (unlikely(notify_page_fault(regs, vec)))
  		return;
  
  	/* Only enable interrupts if they were on before the fault */
  	if ((regs->sr & SR_IMASK) != SR_IMASK)
  		local_irq_enable();
  
  	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
  
  	/*
  	 * If we're in an interrupt, have no user context or are running
  	 * in an atomic region then we must not take the fault:
  	 */
  	if (unlikely(in_atomic() || !mm)) {
  		bad_area_nosemaphore(regs, error_code, address);
  		return;
  	}
  
  retry:
  	down_read(&mm->mmap_sem);
  
  	vma = find_vma(mm, address);
  	if (unlikely(!vma)) {
  		bad_area(regs, error_code, address);
  		return;
  	}
  	if (likely(vma->vm_start <= address))
  		goto good_area;
  	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
  		bad_area(regs, error_code, address);
  		return;
  	}
  	if (unlikely(expand_stack(vma, address))) {
  		bad_area(regs, error_code, address);
  		return;
  	}
  
  	/*
  	 * Ok, we have a good vm_area for this memory access, so
  	 * we can handle it..
  	 */
  good_area:
  	if (unlikely(access_error(error_code, vma))) {
  		bad_area_access_error(regs, error_code, address);
  		return;
  	}
  
  	set_thread_fault_code(error_code);
  
  	if (user_mode(regs))
  		flags |= FAULT_FLAG_USER;
  	if (error_code & FAULT_CODE_WRITE)
  		flags |= FAULT_FLAG_WRITE;
  
  	/*
  	 * 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 (unlikely(fault & (VM_FAULT_RETRY | VM_FAULT_ERROR)))
  		if (mm_fault_error(regs, error_code, address, fault))
  			return;
  
  	if (flags & FAULT_FLAG_ALLOW_RETRY) {
  		if (fault & VM_FAULT_MAJOR) {
  			tsk->maj_flt++;
  			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
  				      regs, address);
  		} else {
  			tsk->min_flt++;
  			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
  				      regs, address);
  		}
  		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);
  }