/*
 * Copyright (C) 2009 Sunplus Core Technology Co., Ltd.
 *  Lennox Wu <lennox.wu@sunplusct.com>
 *  Chen Liqin <liqin.chen@sunplusct.com>
 * Copyright (C) 2012 Regents of the University of California
 *
 * 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.,
 */


#include <linux/mm.h>
#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/perf_event.h>
#include <linux/signal.h>
#include <linux/uaccess.h>

#include <asm/pgalloc.h>
#include <asm/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)
{
        struct task_struct *tsk;
        struct vm_area_struct *vma;
        struct mm_struct *mm;
        unsigned long addr, cause;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
        int fault, code = SEGV_MAPERR;

        cause = regs->scause;
        addr = regs->sbadaddr;

        tsk = current;
        mm = tsk->mm;

        /*
         * 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((addr >= VMALLOC_START) && (addr <= VMALLOC_END)))
                goto vmalloc_fault;

        /* Enable interrupts if they were enabled in the parent context. */
        if (likely(regs->sstatus & SR_SPIE))
                local_irq_enable();

        /*
         * 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(faulthandler_disabled() || !mm))
                goto no_context;

        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);

retry:
        down_read(&mm->mmap_sem);
        vma = find_vma(mm, addr);
        if (unlikely(!vma))
                goto bad_area;
        if (likely(vma->vm_start <= addr))
                goto good_area;
        if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
                goto bad_area;
        if (unlikely(expand_stack(vma, addr)))
                goto bad_area;

        /*
         * Ok, we have a good vm_area for this memory access, so
         * we can handle it.
         */
good_area:
        code = SEGV_ACCERR;

        switch (cause) {
        case EXC_INST_PAGE_FAULT:
                if (!(vma->vm_flags & VM_EXEC))
                        goto bad_area;
                break;
        case EXC_LOAD_PAGE_FAULT:
                if (!(vma->vm_flags & VM_READ))
                        goto bad_area;
                break;
        case EXC_STORE_PAGE_FAULT:
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
                flags |= FAULT_FLAG_WRITE;
                break;
        default:
                panic("%s: unhandled cause %lu", __func__, cause);
        }

        /*
         * If for any reason at all we could not handle the fault,
         * make sure we exit gracefully rather than endlessly redo
         * the fault.
         */
        fault = handle_mm_fault(vma, addr, flags);

        /*
         * If we need to retry but a fatal signal is pending, handle the
         * signal first. We do not need to release the mmap_sem because it
         * would already be released in __lock_page_or_retry in mm/filemap.c.
         */
        if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(tsk))
                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();
        }

        /*
         * Major/minor page fault accounting is only done on the
         * initial attempt. If we go through a retry, it is extremely
         * likely that the page will be found in page cache at that point.
         */
        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, addr);
                } else {
                        tsk->min_flt++;
                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN,
                                      1, regs, addr);
                }
                if (fault & VM_FAULT_RETRY) {
                        /*
                         * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
                         * of starvation.
                         */
                        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);
        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);
        /* User mode accesses just cause a SIGSEGV */
        if (user_mode(regs)) {
                do_trap(regs, SIGSEGV, code, addr, tsk);
                return;
        }

no_context:
        /* Are we prepared to handle this kernel fault? */
        if (fixup_exception(regs))
                return;

        /*
         * Oops. The kernel tried to access some bad page. We'll have to
         * terminate things with extreme prejudice.
         */
        bust_spinlocks(1);
        pr_alert("Unable to handle kernel %s at virtual address " REG_FMT "\n",
                (addr < PAGE_SIZE) ? "NULL pointer dereference" :
                "paging request", addr);
        die(regs, "Oops");
        do_exit(SIGKILL);

        /*
         * 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).
         */
out_of_memory:
        up_read(&mm->mmap_sem);
        if (!user_mode(regs))
                goto no_context;
        pagefault_out_of_memory();
        return;

do_sigbus:
        up_read(&mm->mmap_sem);
        /* Kernel mode? Handle exceptions or die */
        if (!user_mode(regs))
                goto no_context;
        do_trap(regs, SIGBUS, BUS_ADRERR, addr, tsk);
        return;

vmalloc_fault:
        {
                pgd_t *pgd, *pgd_k;
                pud_t *pud, *pud_k;
                p4d_t *p4d, *p4d_k;
                pmd_t *pmd, *pmd_k;
                pte_t *pte_k;
                int index;

                if (user_mode(regs))
                        goto bad_area;

                /*
                 * Synchronize this task's top level page-table
                 * with the 'reference' page table.
                 *
                 * Do _not_ use "tsk->active_mm->pgd" here.
                 * We might be inside an interrupt in the middle
                 * of a task switch.
                 *
                 * Note: Use the old spbtr name instead of using the current
                 * satp name to support binutils 2.29 which doesn't know about
                 * the privileged ISA 1.10 yet.
                 */
                index = pgd_index(addr);
                pgd = (pgd_t *)pfn_to_virt(csr_read(sptbr)) + index;
                pgd_k = init_mm.pgd + index;

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

                p4d = p4d_offset(pgd, addr);
                p4d_k = p4d_offset(pgd_k, addr);
                if (!p4d_present(*p4d_k))
                        goto no_context;

                pud = pud_offset(p4d, addr);
                pud_k = pud_offset(p4d_k, addr);
                if (!pud_present(*pud_k))
                        goto no_context;

                /*
                 * Since the vmalloc area is global, it is unnecessary
                 * to copy individual PTEs
                 */
                pmd = pmd_offset(pud, addr);
                pmd_k = pmd_offset(pud_k, addr);
                if (!pmd_present(*pmd_k))
                        goto no_context;
                set_pmd(pmd, *pmd_k);

                /*
                 * Make sure the actual PTE exists as well to
                 * catch kernel vmalloc-area accesses to non-mapped
                 * addresses. If we don't do this, this will just
                 * silently loop forever.
                 */
                pte_k = pte_offset_kernel(pmd_k, addr);
                if (!pte_present(*pte_k))
                        goto no_context;
                return;
        }
}