/*
 *  Meta page fault handling.
 *
 *  Copyright (C) 2005-2012 Imagination Technologies Ltd.
 */

#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/kernel.h>
#include <linux/ptrace.h>
#include <linux/interrupt.h>
#include <linux/uaccess.h>

#include <asm/tlbflush.h>
#include <asm/mmu.h>
#include <asm/traps.h>

/* Clear any pending catch buffer state. */
static void clear_cbuf_entry(struct pt_regs *regs, unsigned long addr,
                             unsigned int trapno)
{
        PTBICTXEXTCB0 cbuf = regs->extcb0;

        switch (trapno) {
                /* Instruction fetch faults leave no catch buffer state. */
        case TBIXXF_SIGNUM_IGF:
        case TBIXXF_SIGNUM_IPF:
                return;
        default:
                if (cbuf[0].CBAddr == addr) {
                        cbuf[0].CBAddr = 0;
                        cbuf[0].CBFlags &= ~TXCATCH0_FAULT_BITS;

                        /* And, as this is the ONLY catch entry, we
                         * need to clear the cbuf bit from the context!
                         */
                        regs->ctx.SaveMask &= ~(TBICTX_CBUF_BIT |
                                                TBICTX_XCBF_BIT);

                        return;
                }
                pr_err("Failed to clear cbuf entry!\n");
        }
}

int show_unhandled_signals = 1;

int do_page_fault(struct pt_regs *regs, unsigned long address,
                  unsigned int write_access, unsigned int trapno)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct *vma, *prev_vma;
        siginfo_t info;
        int fault;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
                                (write_access ? FAULT_FLAG_WRITE : 0);

        tsk = current;

        if ((address >= VMALLOC_START) && (address < VMALLOC_END)) {
                /*
                 * 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;
                pud_t *pud, *pud_k;
                pmd_t *pmd, *pmd_k;
                pte_t *pte_k;

                pgd = ((pgd_t *)mmu_get_base()) + offset;
                pgd_k = swapper_pg_dir + offset;

                /* This will never happen with the folded page table. */
                if (!pgd_present(*pgd)) {
                        if (!pgd_present(*pgd_k))
                                goto bad_area_nosemaphore;
                        set_pgd(pgd, *pgd_k);
                        return 0;
                }

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

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

                pte_k = pte_offset_kernel(pmd_k, address);
                if (!pte_present(*pte_k))
                        goto bad_area_nosemaphore;

                /* May only be needed on Chorus2 */
                flush_tlb_all();
                return 0;
        }

        mm = tsk->mm;

        if (in_atomic() || !mm)
                goto no_context;

retry:
        down_read(&mm->mmap_sem);

        vma = find_vma_prev(mm, address, &prev_vma);

        if (!vma || address < vma->vm_start)
                goto check_expansion;

good_area:
        if (write_access) {
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
        } else {
                if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                        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(mm, vma, address, flags);

        if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
                return 0;

        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();
        }
        if (flags & FAULT_FLAG_ALLOW_RETRY) {
                if (fault & VM_FAULT_MAJOR)
                        tsk->maj_flt++;
                else
                        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 0;

check_expansion:
        vma = prev_vma;
        if (vma && (expand_stack(vma, address) == 0))
                goto good_area;

bad_area:
        up_read(&mm->mmap_sem);

bad_area_nosemaphore:
        if (user_mode(regs)) {
                info.si_signo = SIGSEGV;
                info.si_errno = 0;
                info.si_code = SEGV_MAPERR;
                info.si_addr = (__force void __user *)address;
                info.si_trapno = trapno;

                if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
                    printk_ratelimit()) {
                        pr_info("%s%s[%d]: segfault at %lx pc %08x sp %08x write %d trap %#x (%s)",
                               task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
                               tsk->comm, task_pid_nr(tsk), address,
                               regs->ctx.CurrPC, regs->ctx.AX[0].U0,
                               write_access, trapno, trap_name(trapno));
                        print_vma_addr(" in ", regs->ctx.CurrPC);
                        print_vma_addr(" rtp in ", regs->ctx.DX[4].U1);
                        printk("\n");
                        show_regs(regs);
                }
                force_sig_info(SIGSEGV, &info, tsk);
                return 1;
        }
        goto no_context;

do_sigbus:
        up_read(&mm->mmap_sem);

        /*
         * Send a sigbus, regardless of whether we were in kernel
         * or user mode.
         */
        info.si_signo = SIGBUS;
        info.si_errno = 0;
        info.si_code = BUS_ADRERR;
        info.si_addr = (__force void __user *)address;
        info.si_trapno = trapno;
        force_sig_info(SIGBUS, &info, tsk);

        /* Kernel mode? Handle exceptions or die */
        if (!user_mode(regs))
                goto no_context;

        return 1;

        /*
         * 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))
                do_group_exit(SIGKILL);

no_context:
        /* Are we prepared to handle this kernel fault?  */
        if (fixup_exception(regs)) {
                clear_cbuf_entry(regs, address, trapno);
                return 1;
        }

        die("Oops", regs, (write_access << 15) | trapno, address);
        do_exit(SIGKILL);
}