/*
 * Page fault handler for SH with an MMU.
 *
 *  Copyright (C) 1999  Niibe Yutaka
 *  Copyright (C) 2003 - 2009  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 <asm/io_trapped.h>
#include <asm/system.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.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 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;

	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;
}

/*
 * 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 < P3_ADDR_MAX))
		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 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 writeaccess,
					unsigned long address)
{
	unsigned long vec;
	struct task_struct *tsk;
	struct mm_struct *mm;
	struct vm_area_struct * vma;
	int si_code;
	int fault;
	siginfo_t info;

	tsk = current;
	mm = tsk->mm;
	si_code = SEGV_MAPERR;
	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;

		goto bad_area_nosemaphore;
	}

	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, 0, 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 (in_atomic() || !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 (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:
	si_code = SEGV_ACCERR;
	if (writeaccess) {
		if (!(vma->vm_flags & VM_WRITE))
			goto bad_area;
	} else {
		if (!(vma->vm_flags & (VM_READ | VM_EXEC | 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, writeaccess ? FAULT_FLAG_WRITE : 0);
	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++;
		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 0,
				     regs, address);
	} else {
		tsk->min_flt++;
		perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 0,
				     regs, address);
	}

	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:
	if (user_mode(regs)) {
		info.si_signo = SIGSEGV;
		info.si_errno = 0;
		info.si_code = si_code;
		info.si_addr = (void *) address;
		force_sig_info(SIGSEGV, &info, tsk);
		return;
	}

no_context:
	/* 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);

	if (oops_may_print()) {
		unsigned long page;

		if (address < PAGE_SIZE)
			printk(KERN_ALERT "Unable to handle kernel NULL "
					  "pointer dereference");
		else
			printk(KERN_ALERT "Unable to handle kernel paging "
					  "request");
		printk(" at virtual address %08lx\n", address);
		printk(KERN_ALERT "pc = %08lx\n", regs->pc);
		page = (unsigned long)get_TTB();
		if (page) {
			page = ((__typeof__(page) *)page)[address >> PGDIR_SHIFT];
			printk(KERN_ALERT "*pde = %08lx\n", page);
			if (page & _PAGE_PRESENT) {
				page &= PAGE_MASK;
				address &= 0x003ff000;
				page = ((__typeof__(page) *)
						__va(page))[address >>
							    PAGE_SHIFT];
				printk(KERN_ALERT "*pte = %08lx\n", page);
			}
		}
	}

	die("Oops", regs, writeaccess);
	bust_spinlocks(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 (is_global_init(current)) {
		yield();
		down_read(&mm->mmap_sem);
		goto survive;
	}
	printk("VM: killing process %s\n", tsk->comm);
	if (user_mode(regs))
		do_group_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;
}

/*
 * Called with interrupts disabled.
 */
asmlinkage int __kprobes
handle_tlbmiss(struct pt_regs *regs, unsigned long writeaccess,
	       unsigned long address)
{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;
	pte_t entry;

	/*
	 * We don't take page faults for P1, P2, and parts of P4, these
	 * are always mapped, whether it be due to legacy behaviour in
	 * 29-bit mode, or due to PMB configuration in 32-bit mode.
	 */
	if (address >= P3SEG && address < P3_ADDR_MAX) {
		pgd = pgd_offset_k(address);
	} else {
		if (unlikely(address >= TASK_SIZE || !current->mm))
			return 1;

		pgd = pgd_offset(current->mm, address);
	}

	pud = pud_offset(pgd, address);
	if (pud_none_or_clear_bad(pud))
		return 1;
	pmd = pmd_offset(pud, address);
	if (pmd_none_or_clear_bad(pmd))
		return 1;
	pte = pte_offset_kernel(pmd, address);
	entry = *pte;
	if (unlikely(pte_none(entry) || pte_not_present(entry)))
		return 1;
	if (unlikely(writeaccess && !pte_write(entry)))
		return 1;

	if (writeaccess)
		entry = pte_mkdirty(entry);
	entry = pte_mkyoung(entry);

	set_pte(pte, entry);

#if defined(CONFIG_CPU_SH4) && !defined(CONFIG_SMP)
	/*
	 * SH-4 does not set MMUCR.RC to the corresponding TLB entry in
	 * the case of an initial page write exception, so we need to
	 * flush it in order to avoid potential TLB entry duplication.
	 */
	if (writeaccess == 2)
		local_flush_tlb_one(get_asid(), address & PAGE_MASK);
#endif

	update_mmu_cache(NULL, address, entry);

	return 0;
}
