/*
 * arch/score/mm/fault.c
 *
 * Score Processor version.
 *
 * Copyright (C) 2009 Sunplus Core Technology Co., Ltd.
 *  Lennox Wu <lennox.wu@sunplusct.com>
 *  Chen Liqin <liqin.chen@sunplusct.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see the file COPYING, or write
 * to the Free Software Foundation, Inc.,
 * 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/module.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>

/*
 * 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 do_page_fault(struct pt_regs *regs, unsigned long write,
                                unsigned long address)
{
        struct vm_area_struct *vma = NULL;
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->mm;
        const int field = sizeof(unsigned long) * 2;
        siginfo_t info;
        int fault;

        info.si_code = SEGV_MAPERR;

        /*
        * 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(address >= VMALLOC_START && address <= VMALLOC_END))
                goto vmalloc_fault;
#ifdef MODULE_START
        if (unlikely(address >= MODULE_START && address < MODULE_END))
                goto vmalloc_fault;
#endif

        /*
        * If we're in an interrupt or have no user
        * context, we must not take the fault..
        */
        if (in_atomic() || !mm)
                goto bad_area_nosemaphore;

        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:
        info.si_code = SEGV_ACCERR;

        if (write) {
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
        } else {
                if (!(vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)))
                        goto bad_area;
        }

survive:
        /*
        * 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(vma, address, write);
        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);

bad_area_nosemaphore:
        /* User mode accesses just cause a SIGSEGV */
        if (user_mode(regs)) {
                tsk->thread.cp0_badvaddr = address;
                tsk->thread.error_code = write;
                info.si_signo = SIGSEGV;
                info.si_errno = 0;
                /* info.si_code has been set above */
                info.si_addr = (void __user *) address;
                force_sig_info(SIGSEGV, &info, tsk);
                return;
        }

no_context:
        /* Are we prepared to handle this kernel fault? */
        if (fixup_exception(regs)) {
                current->thread.cp0_baduaddr = address;
                return;
        }

        /*
        * Oops. The kernel tried to access some bad page. We'll have to
        * terminate things with extreme prejudice.
        */
        bust_spinlocks(1);

        printk(KERN_ALERT "CPU %d Unable to handle kernel paging request at "
                        "virtual address %0*lx, epc == %0*lx, ra == %0*lx\n",
                        0, field, address, field, regs->cp0_epc,
                        field, regs->regs[3]);
        die("Oops", regs);

        /*
        * 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(tsk)) {
                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 */
        if (!user_mode(regs))
                goto no_context;
        else
        /*
        * Send a sigbus, regardless of whether we were in kernel
        * or user mode.
        */
        tsk->thread.cp0_badvaddr = address;
        info.si_signo = SIGBUS;
        info.si_errno = 0;
        info.si_code = BUS_ADRERR;
        info.si_addr = (void __user *) address;
        force_sig_info(SIGBUS, &info, tsk);
        return;
vmalloc_fault:
        {
                /*
                * Synchronize this task's top level page-table
                * with the 'reference' page table.
                *
                * Do _not_ use "tsk" here. We might be inside
                * an interrupt in the middle of a task switch..
                */
                int offset = __pgd_offset(address);
                pgd_t *pgd, *pgd_k;
                pud_t *pud, *pud_k;
                pmd_t *pmd, *pmd_k;
                pte_t *pte_k;

                pgd = (pgd_t *) pgd_current + offset;
                pgd_k = init_mm.pgd + offset;

                if (!pgd_present(*pgd_k))
                        goto no_context;
                set_pgd(pgd, *pgd_k);

                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 no_context;
                set_pmd(pmd, *pmd_k);

                pte_k = pte_offset_kernel(pmd_k, address);
                if (!pte_present(*pte_k))
                        goto no_context;
                return;
        }
}