/*
 * 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.
 *
 * Copyright (C) 1995 - 2000 by Ralf Baechle
 */
#include <linux/context_tracking.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/ratelimit.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/kprobes.h>
#include <linux/perf_event.h>
#include <linux/uaccess.h>

#include <asm/branch.h>
#include <asm/mmu_context.h>
#include <asm/ptrace.h>
#include <asm/highmem.h>                /* For VMALLOC_END */
#include <linux/kdebug.h>

int show_unhandled_signals = 1;

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
static void __kprobes __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;
        int si_code;
        vm_fault_t fault;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

        static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);

#if 0
        printk("Cpu%d[%s:%d:%0*lx:%ld:%0*lx]\n", raw_smp_processor_id(),
               current->comm, current->pid, field, address, write,
               field, regs->cp0_epc);
#endif

#ifdef CONFIG_KPROBES
        /*
         * This is to notify the fault handler of the kprobes.
         */
        if (notify_die(DIE_PAGE_FAULT, "page fault", regs, -1,
                       current->thread.trap_nr, SIGSEGV) == NOTIFY_STOP)
                return;
#endif

        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.
         */
#ifdef CONFIG_64BIT
# define VMALLOC_FAULT_TARGET no_context
#else
# define VMALLOC_FAULT_TARGET vmalloc_fault
#endif

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

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

        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;
retry:
        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 (write) {
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
                flags |= FAULT_FLAG_WRITE;
        } else {
                if (cpu_has_rixi) {
                        if (address == regs->cp0_epc && !(vma->vm_flags & VM_EXEC)) {
#if 0
                                pr_notice("Cpu%d[%s:%d:%0*lx:%ld:%0*lx] XI violation\n",
                                          raw_smp_processor_id(),
                                          current->comm, current->pid,
                                          field, address, write,
                                          field, regs->cp0_epc);
#endif
                                goto bad_area;
                        }
                        if (!(vma->vm_flags & VM_READ) &&
                            exception_epc(regs) != address) {
#if 0
                                pr_notice("Cpu%d[%s:%d:%0*lx:%ld:%0*lx] RI violation\n",
                                          raw_smp_processor_id(),
                                          current->comm, current->pid,
                                          field, address, write,
                                          field, regs->cp0_epc);
#endif
                                goto bad_area;
                        }
                } else {
                        if (!(vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)))
                                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.
         */
        fault = handle_mm_fault(vma, address, flags);

        if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
                return;

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
        if (unlikely(fault & VM_FAULT_ERROR)) {
                if (fault & VM_FAULT_OOM)
                        goto out_of_memory;
                else if (fault & VM_FAULT_SIGSEGV)
                        goto bad_area;
                else if (fault & VM_FAULT_SIGBUS)
                        goto do_sigbus;
                BUG();
        }
        if (flags & FAULT_FLAG_ALLOW_RETRY) {
                if (fault & VM_FAULT_MAJOR) {
                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
                                                  regs, address);
                        tsk->maj_flt++;
                } else {
                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
                                                  regs, address);
                        tsk->min_flt++;
                }
                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);
        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;
                if (show_unhandled_signals &&
                    unhandled_signal(tsk, SIGSEGV) &&
                    __ratelimit(&ratelimit_state)) {
                        pr_info("do_page_fault(): sending SIGSEGV to %s for invalid %s %0*lx\n",
                                tsk->comm,
                                write ? "write access to" : "read access from",
                                field, address);
                        pr_info("epc = %0*lx in", field,
                                (unsigned long) regs->cp0_epc);
                        print_vma_addr(KERN_CONT " ", regs->cp0_epc);
                        pr_cont("\n");
                        pr_info("ra  = %0*lx in", field,
                                (unsigned long) regs->regs[31]);
                        print_vma_addr(KERN_CONT " ", regs->regs[31]);
                        pr_cont("\n");
                }
                current->thread.trap_nr = (regs->cp0_cause >> 2) & 0x1f;
                force_sig_fault(SIGSEGV, si_code, (void __user *)address);
                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",
               raw_smp_processor_id(), field, address, field, regs->cp0_epc,
               field,  regs->regs[31]);
        die("Oops", regs);

out_of_memory:
        /*
         * 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).
         */
        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;

        /*
         * Send a sigbus, regardless of whether we were in kernel
         * or user mode.
         */
#if 0
        printk("do_page_fault() #3: sending SIGBUS to %s for "
               "invalid %s\n%0*lx (epc == %0*lx, ra == %0*lx)\n",
               tsk->comm,
               write ? "write access to" : "read access from",
               field, address,
               field, (unsigned long) regs->cp0_epc,
               field, (unsigned long) regs->regs[31]);
#endif
        current->thread.trap_nr = (regs->cp0_cause >> 2) & 0x1f;
        tsk->thread.cp0_badvaddr = address;
        force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);

        return;
#ifndef CONFIG_64BIT
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_index(address);
                pgd_t *pgd, *pgd_k;
                p4d_t *p4d, *p4d_k;
                pud_t *pud, *pud_k;
                pmd_t *pmd, *pmd_k;
                pte_t *pte_k;

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

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

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

                pud = pud_offset(p4d, address);
                pud_k = pud_offset(p4d_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;
        }
#endif
}

asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
        unsigned long write, unsigned long address)
{
        enum ctx_state prev_state;

        prev_state = exception_enter();
        __do_page_fault(regs, write, address);
        exception_exit(prev_state);
}