// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2005-2017 Andes Technology Corporation

#include <linux/extable.h>
#include <linux/module.h>
#include <linux/signal.h>
#include <linux/ptrace.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/perf_event.h>

#include <asm/pgtable.h>
#include <asm/tlbflush.h>

extern void die(const char *str, struct pt_regs *regs, long err);

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

        pr_alert("pgd = %p\n", mm->pgd);
        pgd = pgd_offset(mm, addr);
        pr_alert("[%08lx] *pgd=%08lx", addr, pgd_val(*pgd));

        do {
                pmd_t *pmd;

                if (pgd_none(*pgd))
                        break;

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

                pmd = pmd_offset(pgd, addr);
#if PTRS_PER_PMD != 1
                pr_alert(", *pmd=%08lx", pmd_val(*pmd));
#endif

                if (pmd_none(*pmd))
                        break;

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

                if (IS_ENABLED(CONFIG_HIGHMEM))
                {
                        pte_t *pte;
                        /* We must not map this if we have highmem enabled */
                        pte = pte_offset_map(pmd, addr);
                        pr_alert(", *pte=%08lx", pte_val(*pte));
                        pte_unmap(pte);
                }
        } while (0);

        pr_alert("\n");
}

void do_page_fault(unsigned long entry, unsigned long addr,
                   unsigned int error_code, struct pt_regs *regs)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct *vma;
        int si_code;
        vm_fault_t fault;
        unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

        error_code = error_code & (ITYPE_mskINST | ITYPE_mskETYPE);
        tsk = current;
        mm = tsk->mm;
        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 (addr >= TASK_SIZE) {
                if (user_mode(regs))
                        goto bad_area_nosemaphore;

                if (addr >= TASK_SIZE && addr < VMALLOC_END
                    && (entry == ENTRY_PTE_NOT_PRESENT))
                        goto vmalloc_fault;
                else
                        goto no_context;
        }

        /* Send a signal to the task for handling the unalignment access. */
        if (entry == ENTRY_GENERAL_EXCPETION
            && error_code == ETYPE_ALIGNMENT_CHECK) {
                if (user_mode(regs))
                        goto bad_area_nosemaphore;
                else
                        goto no_context;
        }

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

        /*
         * As per x86, we may deadlock here. However, since the kernel only
         * validly references user space from well defined areas of the code,
         * we can bug out early if this is from code which shouldn't.
         */
        if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
                if (!user_mode(regs) &&
                    !search_exception_tables(instruction_pointer(regs)))
                        goto no_context;
retry:
                down_read(&mm->mmap_sem);
        } else {
                /*
                 * The above down_read_trylock() might have succeeded in which
                 * case, we'll have missed the might_sleep() from down_read().
                 */
                might_sleep();
                if (IS_ENABLED(CONFIG_DEBUG_VM)) {
                        if (!user_mode(regs) &&
                            !search_exception_tables(instruction_pointer(regs)))
                                goto no_context;
                }
        }

        vma = find_vma(mm, addr);

        if (unlikely(!vma))
                goto bad_area;

        if (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:
        si_code = SEGV_ACCERR;

        /* first do some preliminary protection checks */
        if (entry == ENTRY_PTE_NOT_PRESENT) {
                if (error_code & ITYPE_mskINST)
                        mask = VM_EXEC;
                else {
                        mask = VM_READ | VM_WRITE;
                }
        } else if (entry == ENTRY_TLB_MISC) {
                switch (error_code & ITYPE_mskETYPE) {
                case RD_PROT:
                        mask = VM_READ;
                        break;
                case WRT_PROT:
                        mask = VM_WRITE;
                        flags |= FAULT_FLAG_WRITE;
                        break;
                case NOEXEC:
                        mask = VM_EXEC;
                        break;
                case PAGE_MODIFY:
                        mask = VM_WRITE;
                        flags |= FAULT_FLAG_WRITE;
                        break;
                case ACC_BIT:
                        BUG();
                default:
                        break;
                }

        }
        if (!(vma->vm_flags & mask))
                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, 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(current)) {
                if (!user_mode(regs))
                        goto no_context;
                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;
                else
                        goto bad_area;
        }

        /*
         * 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.
         */
        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
        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) {
                        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.address = addr;
                tsk->thread.error_code = error_code;
                tsk->thread.trap_no = entry;
                force_sig_fault(SIGSEGV, si_code, (void __user *)addr);
                return;
        }

no_context:

        /* Are we prepared to handle this kernel fault?
         *
         * (The kernel has valid exception-points in the source
         *  when it acesses user-memory. When it fails in one
         *  of those points, we find it in a table and do a jump
         *  to some fixup code that loads an appropriate error
         *  code)
         */

        {
                const struct exception_table_entry *entry;

                if ((entry =
                     search_exception_tables(instruction_pointer(regs))) !=
                    NULL) {
                        /* Adjust the instruction pointer in the stackframe */
                        instruction_pointer(regs) = entry->fixup;
                        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 %08lx\n",
                 (addr < PAGE_SIZE) ? "NULL pointer dereference" :
                 "paging request", addr);

        show_pte(mm, addr);
        die("Oops", regs, error_code);
        bust_spinlocks(0);
        do_exit(SIGKILL);

        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 (!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
         */
        tsk->thread.address = addr;
        tsk->thread.error_code = error_code;
        tsk->thread.trap_no = entry;
        force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)addr);

        return;

vmalloc_fault:
        {
                /*
                 * Synchronize this task's top level page-table
                 * with the 'reference' page table.
                 *
                 * Use current_pgd instead of tsk->active_mm->pgd
                 * since the latter might be unavailable if this
                 * code is executed in a misfortunately run irq
                 * (like inside schedule() between switch_mm and
                 *  switch_to...).
                 */

                unsigned int index = pgd_index(addr);
                pgd_t *pgd, *pgd_k;
                pud_t *pud, *pud_k;
                pmd_t *pmd, *pmd_k;
                pte_t *pte_k;

                pgd = (pgd_t *) __va(__nds32__mfsr(NDS32_SR_L1_PPTB)) + index;
                pgd_k = init_mm.pgd + index;

                if (!pgd_present(*pgd_k))
                        goto no_context;

                pud = pud_offset(pgd, addr);
                pud_k = pud_offset(pgd_k, addr);
                if (!pud_present(*pud_k))
                        goto no_context;

                pmd = pmd_offset(pud, addr);
                pmd_k = pmd_offset(pud_k, addr);
                if (!pmd_present(*pmd_k))
                        goto no_context;

                if (!pmd_present(*pmd))
                        set_pmd(pmd, *pmd_k);
                else
                        BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));

                /*
                 * Since the vmalloc area is global, we don't
                 * need to copy individual PTE's, it is enough to
                 * copy the pgd pointer into the pte page of the
                 * root task. If that is there, we'll find our pte if
                 * it exists.
                 */

                /* Make sure the actual PTE exists as well to
                 * catch kernel vmalloc-area accesses to non-mapped
                 * addres. 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;
        }
}