fault.c

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/*
 * 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 <[email protected]>
 * Copyright (C) 2010-2011 Jonas Bonn <[email protected]>
 *
 *      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/module.h>
#include <linux/sched.h>

#include <asm/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;

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;
    siginfo_t info;
    int 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();
    } 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;
    info.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:
    info.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(mm, 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_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)) {
        info.si_signo = SIGSEGV;
        info.si_errno = 0;
        /* info.si_code has been set above */
        info.si_addr = (void *)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 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);
    printk("VM: killing process %s\n", tsk->comm);
    if (user_mode(regs))
        do_exit(SIGKILL);
    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 = (void *)address;
    force_sig_info(SIGBUS, &info, 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 + 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;
    }
}