/*
 * Copyright (C) 2004-2006 Atmel Corporation
 *
 * Based on linux/arch/sh/mm/fault.c:
 *   Copyright (C) 1999  Niibe Yutaka
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/kdebug.h>
#include <linux/kprobes.h>

#include <asm/mmu_context.h>
#include <asm/sysreg.h>
#include <asm/tlb.h>
#include <asm/uaccess.h>

#ifdef CONFIG_KPROBES
static inline int notify_page_fault(struct pt_regs *regs, int trap)
{
        int ret = 0;

        if (!user_mode(regs)) {
                if (kprobe_running() && kprobe_fault_handler(regs, trap))
                        ret = 1;
        }

        return ret;
}
#else
static inline int notify_page_fault(struct pt_regs *regs, int trap)
{
        return 0;
}
#endif

int exception_trace = 1;

/*
 * This routine handles page faults. It determines the address and the
 * problem, and then passes it off to one of the appropriate routines.
 *
 * ecr is the Exception Cause Register. Possible values are:
 *   6:  Protection fault (instruction access)
 *   15: Protection fault (read access)
 *   16: Protection fault (write access)
 *   20: Page not found (instruction access)
 *   24: Page not found (read access)
 *   28: Page not found (write access)
 */
asmlinkage void do_page_fault(unsigned long ecr, struct pt_regs *regs)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct *vma;
        const struct exception_table_entry *fixup;
        unsigned long address;
        unsigned long page;
        int writeaccess;
        long signr;
        int code;
        int fault;

        if (notify_page_fault(regs, ecr))
                return;

        address = sysreg_read(TLBEAR);

        tsk = current;
        mm = tsk->mm;

        signr = SIGSEGV;
        code = SEGV_MAPERR;

        /*
         * If we're in an interrupt or have no user context, we must
         * not take the fault...
         */
        if (in_atomic() || !mm || regs->sr & SYSREG_BIT(GM))
                goto no_context;

        local_irq_enable();

        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:
        code = SEGV_ACCERR;
        writeaccess = 0;

        switch (ecr) {
        case ECR_PROTECTION_X:
        case ECR_TLB_MISS_X:
                if (!(vma->vm_flags & VM_EXEC))
                        goto bad_area;
                break;
        case ECR_PROTECTION_R:
        case ECR_TLB_MISS_R:
                if (!(vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)))
                        goto bad_area;
                break;
        case ECR_PROTECTION_W:
        case ECR_TLB_MISS_W:
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
                writeaccess = 1;
                break;
        default:
                panic("Unhandled case %lu in do_page_fault!", ecr);
        }

        /*
         * 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++;
        else
                tsk->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)) {
                if (exception_trace && printk_ratelimit())
                        printk("%s%s[%d]: segfault at %08lx pc %08lx "
                               "sp %08lx ecr %lu\n",
                               is_global_init(tsk) ? KERN_EMERG : KERN_INFO,
                               tsk->comm, tsk->pid, address, regs->pc,
                               regs->sp, ecr);
                _exception(SIGSEGV, regs, code, address);
                return;
        }

no_context:
        /* Are we prepared to handle this kernel fault? */
        fixup = search_exception_tables(regs->pc);
        if (fixup) {
                regs->pc = fixup->fixup;
                return;
        }

        /*
         * Oops. The kernel tried to access some bad page. We'll have
         * to terminate things with extreme prejudice.
         */
        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);

        page = sysreg_read(PTBR);
        printk(KERN_ALERT "ptbr = %08lx", page);
        if (address >= TASK_SIZE)
                page = (unsigned long)swapper_pg_dir;
        if (page) {
                page = ((unsigned long *)page)[address >> 22];
                printk(" pgd = %08lx", page);
                if (page & _PAGE_PRESENT) {
                        page &= PAGE_MASK;
                        address &= 0x003ff000;
                        page = ((unsigned long *)__va(page))[address >> PAGE_SHIFT];
                        printk(" pte = %08lx", page);
                }
        }
        printk("\n");
        die("Kernel access of bad area", regs, signr);
        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", tsk->comm);
        if (user_mode(regs))
                do_group_exit(SIGKILL);
        goto no_context;

do_sigbus:
        up_read(&mm->mmap_sem);

        /* Kernel mode? Handle exceptions or die */
        signr = SIGBUS;
        code = BUS_ADRERR;
        if (!user_mode(regs))
                goto no_context;

        if (exception_trace)
                printk("%s%s[%d]: bus error at %08lx pc %08lx "
                       "sp %08lx ecr %lu\n",
                       is_global_init(tsk) ? KERN_EMERG : KERN_INFO,
                       tsk->comm, tsk->pid, address, regs->pc,
                       regs->sp, ecr);

        _exception(SIGBUS, regs, BUS_ADRERR, address);
}

asmlinkage void do_bus_error(unsigned long addr, int write_access,
                             struct pt_regs *regs)
{
        printk(KERN_ALERT
               "Bus error at physical address 0x%08lx (%s access)\n",
               addr, write_access ? "write" : "read");
        printk(KERN_INFO "DTLB dump:\n");
        dump_dtlb();
        die("Bus Error", regs, SIGKILL);
}