/*
 * OpenRISC fault.c
 *
 * Linux architectural port borrowing liberally from similar works of
 * others.  All original copyrights apply as per the original source
 * declaration.
 *
 * Modifications for the OpenRISC architecture:
 * Copyright (C) 2003 Matjaz Breskvar <phoenix@bsemi.com>
 * Copyright (C) 2010-2011 Jonas Bonn <jonas@southpole.se>
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */

#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/extable.h>
#include <linux/sched/signal.h>

#include <linux/uaccess.h>
#include <asm/siginfo.h>
#include <asm/signal.h>

#define NUM_TLB_ENTRIES 64
#define TLB_OFFSET(add) (((add) >> PAGE_SHIFT) & (NUM_TLB_ENTRIES-1))

unsigned long pte_misses;       /* updated by do_page_fault() */
unsigned long pte_errors;       /* updated by do_page_fault() */

/* __PHX__ :: - check the vmalloc_fault in do_page_fault()
 *            - also look into include/asm-or32/mmu_context.h
 */
volatile pgd_t *current_pgd[NR_CPUS];

extern void die(char *, struct pt_regs *, long);

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * If this routine detects a bad access, it returns 1, otherwise it
 * returns 0.
 */

asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
                              unsigned long vector, int write_acc)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct *vma;
        int si_code;
        vm_fault_t fault;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

        tsk = current;

        /*
         * 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.
         *
         * NOTE2: This is done so that, when updating the vmalloc
         * mappings we don't have to walk all processes pgdirs and
         * add the high mappings all at once. Instead we do it as they
         * are used. However vmalloc'ed page entries have the PAGE_GLOBAL
         * bit set so sometimes the TLB can use a lingering entry.
         *
         * This verifies that the fault happens in kernel space
         * and that the fault was not a protection error.
         */

        if (address >= VMALLOC_START &&
            (vector != 0x300 && vector != 0x400) &&
            !user_mode(regs))
                goto vmalloc_fault;

        /* If exceptions were enabled, we can reenable them here */
        if (user_mode(regs)) {
                /* Exception was in userspace: reenable interrupts */
                local_irq_enable();
                flags |= FAULT_FLAG_USER;
        } else {
                /* If exception was in a syscall, then IRQ's may have
                 * been enabled or disabled.  If they were enabled,
                 * reenable them.
                 */
                if (regs->sr && (SPR_SR_IEE | SPR_SR_TEE))
                        local_irq_enable();
        }

        mm = tsk->mm;
        si_code = SEGV_MAPERR;

        /*
         * If we're in an interrupt or have no user
         * context, we must not take the fault..
         */

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

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 (user_mode(regs)) {
                /*
                 * accessing the stack below usp is always a bug.
                 * we get page-aligned addresses so we can only check
                 * if we're within a page from usp, but that might be
                 * enough to catch brutal errors at least.
                 */
                if (address + PAGE_SIZE < regs->sp)
                        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;

        /* first do some preliminary protection checks */

        if (write_acc) {
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
                flags |= FAULT_FLAG_WRITE;
        } else {
                /* not present */
                if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
                        goto bad_area;
        }

        /* are we trying to execute nonexecutable area */
        if ((vector == 0x400) && !(vma->vm_page_prot.pgprot & _PAGE_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;

        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) {
                /*RGD modeled on Cris */
                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;

        /*
         * 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)) {
                force_sig_fault(SIGSEGV, si_code, (void __user *)address, tsk);
                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;

                __asm__ __volatile__("l.nop 42");

                if ((entry = search_exception_tables(regs->pc)) != NULL) {
                        /* Adjust the instruction pointer in the stackframe */
                        regs->pc = entry->fixup;
                        return;
                }
        }

        /*
         * Oops. The kernel tried to access some bad page. We'll have to
         * terminate things with extreme prejudice.
         */

        if ((unsigned long)(address) < PAGE_SIZE)
                printk(KERN_ALERT
                       "Unable to handle kernel NULL pointer dereference");
        else
                printk(KERN_ALERT "Unable to handle kernel access");
        printk(" at virtual address 0x%08lx\n", address);

        die("Oops", regs, write_acc);

        do_exit(SIGKILL);

        /*
         * 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:
        __asm__ __volatile__("l.nop 42");
        __asm__ __volatile__("l.nop 1");

        up_read(&mm->mmap_sem);
        if (!user_mode(regs))
                goto no_context;
        pagefault_out_of_memory();
        return;

do_sigbus:
        up_read(&mm->mmap_sem);

        /*
         * Send a sigbus, regardless of whether we were in kernel
         * or user mode.
         */
        force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address, tsk);

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

                int offset = pgd_index(address);
                pgd_t *pgd, *pgd_k;
                pud_t *pud, *pud_k;
                pmd_t *pmd, *pmd_k;
                pte_t *pte_k;

/*
                phx_warn("do_page_fault(): vmalloc_fault will not work, "
                         "since current_pgd assign a proper value somewhere\n"
                         "anyhow we don't need this at the moment\n");

                phx_mmu("vmalloc_fault");
*/
                pgd = (pgd_t *)current_pgd[smp_processor_id()] + offset;
                pgd_k = init_mm.pgd + offset;

                /* Since we're two-level, we don't need to do both
                 * set_pgd and set_pmd (they do the same thing). If
                 * we go three-level at some point, do the right thing
                 * with pgd_present and set_pgd here.
                 *
                 * Also, 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.
                 */

                pud = pud_offset(pgd, address);
                pud_k = pud_offset(pgd_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 bad_area_nosemaphore;

                set_pmd(pmd, *pmd_k);

                /* Make sure the actual PTE exists as well to
                 * catch kernel vmalloc-area accesses to non-mapped
                 * addresses. If we don't do this, this will just
                 * silently loop forever.
                 */

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

                return;
        }
}