fault.c

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/*
 *  arch/microblaze/mm/fault.c
 *
 *    Copyright (C) 2007 Xilinx, Inc.  All rights reserved.
 *
 *  Derived from "arch/ppc/mm/fault.c"
 *    Copyright (C) 1995-1996 Gary Thomas ([email protected])
 *
 *  Derived from "arch/i386/mm/fault.c"
 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Modified by Cort Dougan and Paul Mackerras.
 *
 * This file is subject to the terms and conditions of the GNU General
 * Public License.  See the file COPYING in the main directory of this
 * archive for more details.
 *
 */

#include <linux/module.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/interrupt.h>

#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
#include <linux/uaccess.h>
#include <asm/exceptions.h>

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

/*
 * Check whether the instruction at regs->pc is a store using
 * an update addressing form which will update r1.
 */
static int store_updates_sp(struct pt_regs *regs)
{
    unsigned int inst;

    if (get_user(inst, (unsigned int __user *)regs->pc))
        return 0;
    /* check for 1 in the rD field */
    if (((inst >> 21) & 0x1f) != 1)
        return 0;
    /* check for store opcodes */
    if ((inst & 0xd0000000) == 0xd0000000)
        return 1;
    return 0;
}


/*
 * bad_page_fault is called when we have a bad access from the kernel.
 * It is called from do_page_fault above and from some of the procedures
 * in traps.c.
 */
void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
    const struct exception_table_entry *fixup;
/* MS: no context */
    /* Are we prepared to handle this fault?  */
    fixup = search_exception_tables(regs->pc);
    if (fixup) {
        regs->pc = fixup->fixup;
        return;
    }

    /* kernel has accessed a bad area */
    die("kernel access of bad area", regs, sig);
}

/*
 * The error_code parameter is ESR for a data fault,
 * 0 for an instruction fault.
 */
void do_page_fault(struct pt_regs *regs, unsigned long address,
           unsigned long error_code)
{
    struct vm_area_struct *vma;
    struct mm_struct *mm = current->mm;
    siginfo_t info;
    int code = SEGV_MAPERR;
    int is_write = error_code & ESR_S;
    int fault;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
                     (is_write ? FAULT_FLAG_WRITE : 0);

    regs->ear = address;
    regs->esr = error_code;

    /* On a kernel SLB miss we can only check for a valid exception entry */
    if (unlikely(kernel_mode(regs) && (address >= TASK_SIZE))) {
        printk(KERN_WARNING "kernel task_size exceed");
        _exception(SIGSEGV, regs, code, address);
    }

    /* for instr TLB miss and instr storage exception ESR_S is undefined */
    if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11)
        is_write = 0;

    if (unlikely(in_atomic() || !mm)) {
        if (kernel_mode(regs))
            goto bad_area_nosemaphore;

        /* in_atomic() in user mode is really bad,
           as is current->mm == NULL. */
        printk(KERN_EMERG "Page fault in user mode with "
               "in_atomic(), mm = %p\n", mm);
        printk(KERN_EMERG "r15 = %lx  MSR = %lx\n",
               regs->r15, regs->msr);
        die("Weird page fault", regs, SIGSEGV);
    }

    /* When running in the kernel we expect faults to occur only to
     * addresses in user space.  All other faults represent errors in the
     * kernel and should generate an OOPS.  Unfortunately, in the case of an
     * erroneous fault occurring in a code path which already holds mmap_sem
     * we will deadlock attempting to validate the fault against the
     * address space.  Luckily the kernel only validly references user
     * space from well defined areas of code, which are listed in the
     * exceptions table.
     *
     * As the vast majority of faults will be valid we will only perform
     * the source reference check when there is a possibility of a deadlock.
     * Attempt to lock the address space, if we cannot we then validate the
     * source.  If this is invalid we can skip the address space check,
     * thus avoiding the deadlock.
     */
    if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
        if (kernel_mode(regs) && !search_exception_tables(regs->pc))
            goto bad_area_nosemaphore;

retry:
        down_read(&mm->mmap_sem);
    }

    vma = find_vma(mm, address);
    if (unlikely(!vma))
        goto bad_area;

    if (vma->vm_start <= address)
        goto good_area;

    if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
        goto bad_area;

    if (unlikely(!is_write))
        goto bad_area;

    /*
     * N.B. The ABI allows programs to access up to
     * a few hundred bytes below the stack pointer (TBD).
     * The kernel signal delivery code writes up to about 1.5kB
     * below the stack pointer (r1) before decrementing it.
     * The exec code can write slightly over 640kB to the stack
     * before setting the user r1.  Thus we allow the stack to
     * expand to 1MB without further checks.
     */
    if (unlikely(address + 0x100000 < vma->vm_end)) {

        /* get user regs even if this fault is in kernel mode */
        struct pt_regs *uregs = current->thread.regs;
        if (uregs == NULL)
            goto bad_area;

        /*
         * A user-mode access to an address a long way below
         * the stack pointer is only valid if the instruction
         * is one which would update the stack pointer to the
         * address accessed if the instruction completed,
         * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
         * (or the byte, halfword, float or double forms).
         *
         * If we don't check this then any write to the area
         * between the last mapped region and the stack will
         * expand the stack rather than segfaulting.
         */
        if (address + 2048 < uregs->r1
            && (kernel_mode(regs) || !store_updates_sp(regs)))
                goto bad_area;
    }
    if (expand_stack(vma, address))
        goto bad_area;

good_area:
    code = SEGV_ACCERR;

    /* a write */
    if (unlikely(is_write)) {
        if (unlikely(!(vma->vm_flags & VM_WRITE)))
            goto bad_area;
    /* a read */
    } else {
        /* protection fault */
        if (unlikely(error_code & 0x08000000))
            goto bad_area;
        if (unlikely(!(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(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) {
        if (unlikely(fault & VM_FAULT_MAJOR))
            current->maj_flt++;
        else
            current->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);

    /*
     * keep track of tlb+htab misses that are good addrs but
     * just need pte's created via handle_mm_fault()
     * -- Cort
     */
    pte_misses++;
    return;

bad_area:
    up_read(&mm->mmap_sem);

bad_area_nosemaphore:
    pte_errors++;

    /* User mode accesses cause a SIGSEGV */
    if (user_mode(regs)) {
        _exception(SIGSEGV, regs, code, address);
/*      info.si_signo = SIGSEGV;
        info.si_errno = 0;
        info.si_code = code;
        info.si_addr = (void *) address;
        force_sig_info(SIGSEGV, &info, current);*/
        return;
    }

    bad_page_fault(regs, address, SIGSEGV);
    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))
        bad_page_fault(regs, address, SIGKILL);
    else
        pagefault_out_of_memory();
    return;

do_sigbus:
    up_read(&mm->mmap_sem);
    if (user_mode(regs)) {
        info.si_signo = SIGBUS;
        info.si_errno = 0;
        info.si_code = BUS_ADRERR;
        info.si_addr = (void __user *)address;
        force_sig_info(SIGBUS, &info, current);
        return;
    }
    bad_page_fault(regs, address, SIGBUS);
}