/*
 * Page fault handler for SH with an MMU.
 *
 *  Copyright (C) 1999  Niibe Yutaka
 *  Copyright (C) 2003 - 2012  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/sched/signal.h>
#include <linux/hardirq.h>
#include <linux/kprobes.h>
#include <linux/perf_event.h>
#include <linux/kdebug.h>
#include <linux/uaccess.h>
#include <asm/io_trapped.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#include <asm/traps.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 void
force_sig_info_fault(int si_signo, int si_code, unsigned long address,
                     struct task_struct *tsk)
{
        siginfo_t info;

        info.si_signo   = si_signo;
        info.si_errno   = 0;
        info.si_code    = si_code;
        info.si_addr    = (void __user *)address;

        force_sig_info(si_signo, &info, tsk);
}

/*
 * This is useful to dump out the page tables associated with
 * 'addr' in mm 'mm'.
 */
static void show_pte(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;

        if (mm) {
                pgd = mm->pgd;
        } else {
                pgd = get_TTB();

                if (unlikely(!pgd))
                        pgd = swapper_pg_dir;
        }

        printk(KERN_ALERT "pgd = %p\n", pgd);
        pgd += pgd_index(addr);
        printk(KERN_ALERT "[%08lx] *pgd=%0*Lx", addr,
               (u32)(sizeof(*pgd) * 2), (u64)pgd_val(*pgd));

        do {
                pud_t *pud;
                pmd_t *pmd;
                pte_t *pte;

                if (pgd_none(*pgd))
                        break;

                if (pgd_bad(*pgd)) {
                        printk("(bad)");
                        break;
                }

                pud = pud_offset(pgd, addr);
                if (PTRS_PER_PUD != 1)
                        printk(", *pud=%0*Lx", (u32)(sizeof(*pud) * 2),
                               (u64)pud_val(*pud));

                if (pud_none(*pud))
                        break;

                if (pud_bad(*pud)) {
                        printk("(bad)");
                        break;
                }

                pmd = pmd_offset(pud, addr);
                if (PTRS_PER_PMD != 1)
                        printk(", *pmd=%0*Lx", (u32)(sizeof(*pmd) * 2),
                               (u64)pmd_val(*pmd));

                if (pmd_none(*pmd))
                        break;

                if (pmd_bad(*pmd)) {
                        printk("(bad)");
                        break;
                }

                /* We must not map this if we have highmem enabled */
                if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
                        break;

                pte = pte_offset_kernel(pmd, addr);
                printk(", *pte=%0*Lx", (u32)(sizeof(*pte) * 2),
                       (u64)pte_val(*pte));
        } while (0);

        printk("\n");
}

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;

        if (!pud_present(*pud))
            set_pud(pud, *pud_k);

        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;
}

#ifdef CONFIG_SH_STORE_QUEUES
#define __FAULT_ADDR_LIMIT      P3_ADDR_MAX
#else
#define __FAULT_ADDR_LIMIT      VMALLOC_END
#endif

/*
 * 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 < __FAULT_ADDR_LIMIT))
                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 void
show_fault_oops(struct pt_regs *regs, unsigned long address)
{
        if (!oops_may_print())
                return;

        printk(KERN_ALERT "BUG: unable to handle kernel ");
        if (address < PAGE_SIZE)
                printk(KERN_CONT "NULL pointer dereference");
        else
                printk(KERN_CONT "paging request");

        printk(KERN_CONT " at %08lx\n", address);
        printk(KERN_ALERT "PC:");
        printk_address(regs->pc, 1);

        show_pte(NULL, address);
}

static noinline void
no_context(struct pt_regs *regs, unsigned long error_code,
           unsigned long address)
{
        /* 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);

        show_fault_oops(regs, address);

        die("Oops", regs, error_code);
        bust_spinlocks(0);
        do_exit(SIGKILL);
}

static void
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
                       unsigned long address, int si_code)
{
        struct task_struct *tsk = current;

        /* User mode accesses just cause a SIGSEGV */
        if (user_mode(regs)) {
                /*
                 * It's possible to have interrupts off here:
                 */
                local_irq_enable();

                force_sig_info_fault(SIGSEGV, si_code, address, tsk);

                return;
        }

        no_context(regs, error_code, address);
}

static noinline void
bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
                     unsigned long address)
{
        __bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR);
}

static void
__bad_area(struct pt_regs *regs, unsigned long error_code,
           unsigned long address, int si_code)
{
        struct mm_struct *mm = current->mm;

        /*
         * Something tried to access memory that isn't in our memory map..
         * Fix it, but check if it's kernel or user first..
         */
        up_read(&mm->mmap_sem);

        __bad_area_nosemaphore(regs, error_code, address, si_code);
}

static noinline void
bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
        __bad_area(regs, error_code, address, SEGV_MAPERR);
}

static noinline void
bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
                      unsigned long address)
{
        __bad_area(regs, error_code, address, SEGV_ACCERR);
}

static void
do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->mm;

        up_read(&mm->mmap_sem);

        /* Kernel mode? Handle exceptions or die: */
        if (!user_mode(regs))
                no_context(regs, error_code, address);

        force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
}

static noinline int
mm_fault_error(struct pt_regs *regs, unsigned long error_code,
               unsigned long address, unsigned int fault)
{
        /*
         * Pagefault was interrupted by SIGKILL. We have no reason to
         * continue pagefault.
         */
        if (fatal_signal_pending(current)) {
                if (!(fault & VM_FAULT_RETRY))
                        up_read(&current->mm->mmap_sem);
                if (!user_mode(regs))
                        no_context(regs, error_code, address);
                return 1;
        }

        if (!(fault & VM_FAULT_ERROR))
                return 0;

        if (fault & VM_FAULT_OOM) {
                /* Kernel mode? Handle exceptions or die: */
                if (!user_mode(regs)) {
                        up_read(&current->mm->mmap_sem);
                        no_context(regs, error_code, address);
                        return 1;
                }
                up_read(&current->mm->mmap_sem);

                /*
                 * 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):
                 */
                pagefault_out_of_memory();
        } else {
                if (fault & VM_FAULT_SIGBUS)
                        do_sigbus(regs, error_code, address);
                else if (fault & VM_FAULT_SIGSEGV)
                        bad_area(regs, error_code, address);
                else
                        BUG();
        }

        return 1;
}

static inline int access_error(int error_code, struct vm_area_struct *vma)
{
        if (error_code & FAULT_CODE_WRITE) {
                /* write, present and write, not present: */
                if (unlikely(!(vma->vm_flags & VM_WRITE)))
                        return 1;
                return 0;
        }

        /* ITLB miss on NX page */
        if (unlikely((error_code & FAULT_CODE_ITLB) &&
                     !(vma->vm_flags & VM_EXEC)))
                return 1;

        /* read, not present: */
        if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
                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 error_code,
                                        unsigned long address)
{
        unsigned long vec;
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct * vma;
        int fault;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

        tsk = current;
        mm = tsk->mm;
        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;

                bad_area_nosemaphore(regs, error_code, address);
                return;
        }

        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, regs, address);

        /*
         * If we're in an interrupt, have no user context or are running
         * with pagefaults disabled then we must not take the fault:
         */
        if (unlikely(faulthandler_disabled() || !mm)) {
                bad_area_nosemaphore(regs, error_code, address);
                return;
        }

retry:
        down_read(&mm->mmap_sem);

        vma = find_vma(mm, address);
        if (unlikely(!vma)) {
                bad_area(regs, error_code, address);
                return;
        }
        if (likely(vma->vm_start <= address))
                goto good_area;
        if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
                bad_area(regs, error_code, address);
                return;
        }
        if (unlikely(expand_stack(vma, address))) {
                bad_area(regs, error_code, address);
                return;
        }

        /*
         * Ok, we have a good vm_area for this memory access, so
         * we can handle it..
         */
good_area:
        if (unlikely(access_error(error_code, vma))) {
                bad_area_access_error(regs, error_code, address);
                return;
        }

        set_thread_fault_code(error_code);

        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;
        if (error_code & FAULT_CODE_WRITE)
                flags |= FAULT_FLAG_WRITE;

        /*
         * 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 (unlikely(fault & (VM_FAULT_RETRY | VM_FAULT_ERROR)))
                if (mm_fault_error(regs, error_code, address, fault))
                        return;

        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, address);
                } else {
                        tsk->min_flt++;
                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
                                      regs, address);
                }
                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);
}