/* Page Fault Handling for ARC (TLB Miss / ProtV)
 *
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/signal.h>
#include <linux/interrupt.h>
#include <linux/sched/signal.h>
#include <linux/errno.h>
#include <linux/ptrace.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
#include <linux/perf_event.h>
#include <linux/mm_types.h>
#include <asm/pgalloc.h>
#include <asm/mmu.h>

/*
 * kernel virtual address is required to implement vmalloc/pkmap/fixmap
 * Refer to asm/processor.h for System Memory Map
 *
 * It simply copies the PMD entry (pointer to 2nd level page table or hugepage)
 * from swapper pgdir to task pgdir. The 2nd level table/page is thus shared
 */
noinline static int handle_kernel_vaddr_fault(unsigned long address)
{
        /*
         * Synchronize this task's top level page-table
         * with the 'reference' page table.
         */
        pgd_t *pgd, *pgd_k;
        pud_t *pud, *pud_k;
        pmd_t *pmd, *pmd_k;

        pgd = pgd_offset_fast(current->active_mm, address);
        pgd_k = pgd_offset_k(address);

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

        pud = pud_offset(pgd, address);
        pud_k = pud_offset(pgd_k, address);
        if (!pud_present(*pud_k))
                goto bad_area;

        pmd = pmd_offset(pud, address);
        pmd_k = pmd_offset(pud_k, address);
        if (!pmd_present(*pmd_k))
                goto bad_area;

        set_pmd(pmd, *pmd_k);

        /* XXX: create the TLB entry here */
        return 0;

bad_area:
        return 1;
}

void do_page_fault(unsigned long address, struct pt_regs *regs)
{
        struct vm_area_struct *vma = NULL;
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->mm;
        siginfo_t info;
        int ret;
        vm_fault_t fault;
        int write = regs->ecr_cause & ECR_C_PROTV_STORE;  /* ST/EX */
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

        clear_siginfo(&info);

        /*
         * 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 (address >= VMALLOC_START) {
                ret = handle_kernel_vaddr_fault(address);
                if (unlikely(ret))
                        goto bad_area_nosemaphore;
                else
                        return;
        }

        info.si_code = SEGV_MAPERR;

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

        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:
        info.si_code = SEGV_ACCERR;

        /* Handle protection violation, execute on heap or stack */

        if ((regs->ecr_vec == ECR_V_PROTV) &&
            (regs->ecr_cause == ECR_C_PROTV_INST_FETCH))
                goto bad_area;

        if (write) {
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
                flags |= FAULT_FLAG_WRITE;
        } else {
                if (!(vma->vm_flags & (VM_READ | 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 Pagefault was interrupted by SIGKILL, exit page fault "early" */
        if (unlikely(fatal_signal_pending(current))) {
                if ((fault & VM_FAULT_ERROR) && !(fault & VM_FAULT_RETRY))
                        up_read(&mm->mmap_sem);
                if (user_mode(regs))
                        return;
        }

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

        if (likely(!(fault & VM_FAULT_ERROR))) {
                if (flags & FAULT_FLAG_ALLOW_RETRY) {
                        /* To avoid updating stats twice for retry case */
                        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;
                                goto retry;
                        }
                }

                /* Fault Handled Gracefully */
                up_read(&mm->mmap_sem);
                return;
        }

        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;

        /* no man's land */
        BUG();

        /*
         * 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.fault_address = address;
                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?
         *
         * (The kernel has valid exception-points in the source
         *  when it accesses 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)
         */
        if (fixup_exception(regs))
                return;

        die("Oops", regs, address);

out_of_memory:
        up_read(&mm->mmap_sem);

        if (user_mode(regs)) {
                pagefault_out_of_memory();
                return;
        }

        goto no_context;

do_sigbus:
        up_read(&mm->mmap_sem);

        if (!user_mode(regs))
                goto no_context;

        tsk->thread.fault_address = 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);
}