fault.c

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/*
 * Page fault handler for SH with an MMU.
 *
 *  Copyright (C) 1999  Niibe Yutaka
 *  Copyright (C) 2003 - 2012  Paul Mundt
 *
 *  Based on linux/arch/i386/mm/fault.c:
 *   Copyright (C) 1995  Linus Torvalds
 *
 * 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/kernel.h>
#include <linux/mm.h>
#include <linux/hardirq.h>
#include <linux/kprobes.h>
#include <linux/perf_event.h>
#include <linux/kdebug.h>
#include <asm/io_trapped.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#include <asm/traps.h>

static inline int notify_page_fault(struct pt_regs *regs, int trap)
{
    int ret = 0;

    if (kprobes_built_in() && !user_mode(regs)) {
        preempt_disable();
        if (kprobe_running() && kprobe_fault_handler(regs, trap))
            ret = 1;
        preempt_enable();
    }

    return ret;
}

static void
force_sig_info_fault(int si_signo, int si_code, unsigned long address,
             struct task_struct *tsk)
{
    siginfo_t info;

    info.si_signo   = si_signo;
    info.si_errno   = 0;
    info.si_code    = si_code;
    info.si_addr    = (void __user *)address;

    force_sig_info(si_signo, &info, tsk);
}

/*
 * This is useful to dump out the page tables associated with
 * 'addr' in mm 'mm'.
 */
static void show_pte(struct mm_struct *mm, unsigned long addr)
{
    pgd_t *pgd;

    if (mm) {
        pgd = mm->pgd;
    } else {
        pgd = get_TTB();

        if (unlikely(!pgd))
            pgd = swapper_pg_dir;
    }

    printk(KERN_ALERT "pgd = %p\n", pgd);
    pgd += pgd_index(addr);
    printk(KERN_ALERT "[%08lx] *pgd=%0*Lx", addr,
           (u32)(sizeof(*pgd) * 2), (u64)pgd_val(*pgd));

    do {
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

        if (pgd_none(*pgd))
            break;

        if (pgd_bad(*pgd)) {
            printk("(bad)");
            break;
        }

        pud = pud_offset(pgd, addr);
        if (PTRS_PER_PUD != 1)
            printk(", *pud=%0*Lx", (u32)(sizeof(*pud) * 2),
                   (u64)pud_val(*pud));

        if (pud_none(*pud))
            break;

        if (pud_bad(*pud)) {
            printk("(bad)");
            break;
        }

        pmd = pmd_offset(pud, addr);
        if (PTRS_PER_PMD != 1)
            printk(", *pmd=%0*Lx", (u32)(sizeof(*pmd) * 2),
                   (u64)pmd_val(*pmd));

        if (pmd_none(*pmd))
            break;

        if (pmd_bad(*pmd)) {
            printk("(bad)");
            break;
        }

        /* We must not map this if we have highmem enabled */
        if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
            break;

        pte = pte_offset_kernel(pmd, addr);
        printk(", *pte=%0*Lx", (u32)(sizeof(*pte) * 2),
               (u64)pte_val(*pte));
    } while (0);

    printk("\n");
}

static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
{
    unsigned index = pgd_index(address);
    pgd_t *pgd_k;
    pud_t *pud, *pud_k;
    pmd_t *pmd, *pmd_k;

    pgd += index;
    pgd_k = init_mm.pgd + index;

    if (!pgd_present(*pgd_k))
        return NULL;

    pud = pud_offset(pgd, address);
    pud_k = pud_offset(pgd_k, address);
    if (!pud_present(*pud_k))
        return NULL;

    if (!pud_present(*pud))
        set_pud(pud, *pud_k);

    pmd = pmd_offset(pud, address);
    pmd_k = pmd_offset(pud_k, address);
    if (!pmd_present(*pmd_k))
        return NULL;

    if (!pmd_present(*pmd))
        set_pmd(pmd, *pmd_k);
    else {
        /*
         * The page tables are fully synchronised so there must
         * be another reason for the fault. Return NULL here to
         * signal that we have not taken care of the fault.
         */
        BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
        return NULL;
    }

    return pmd_k;
}

#ifdef CONFIG_SH_STORE_QUEUES
#define __FAULT_ADDR_LIMIT  P3_ADDR_MAX
#else
#define __FAULT_ADDR_LIMIT  VMALLOC_END
#endif

/*
 * Handle a fault on the vmalloc or module mapping area
 */
static noinline int vmalloc_fault(unsigned long address)
{
    pgd_t *pgd_k;
    pmd_t *pmd_k;
    pte_t *pte_k;

    /* Make sure we are in vmalloc/module/P3 area: */
    if (!(address >= VMALLOC_START && address < __FAULT_ADDR_LIMIT))
        return -1;

    /*
     * Synchronize this task's top level page-table
     * with the 'reference' page table.
     *
     * Do _not_ use "current" here. We might be inside
     * an interrupt in the middle of a task switch..
     */
    pgd_k = get_TTB();
    pmd_k = vmalloc_sync_one(pgd_k, address);
    if (!pmd_k)
        return -1;

    pte_k = pte_offset_kernel(pmd_k, address);
    if (!pte_present(*pte_k))
        return -1;

    return 0;
}

static void
show_fault_oops(struct pt_regs *regs, unsigned long address)
{
    if (!oops_may_print())
        return;

    printk(KERN_ALERT "BUG: unable to handle kernel ");
    if (address < PAGE_SIZE)
        printk(KERN_CONT "NULL pointer dereference");
    else
        printk(KERN_CONT "paging request");

    printk(KERN_CONT " at %08lx\n", address);
    printk(KERN_ALERT "PC:");
    printk_address(regs->pc, 1);

    show_pte(NULL, address);
}

static noinline void
no_context(struct pt_regs *regs, unsigned long error_code,
       unsigned long address)
{
    /* Are we prepared to handle this kernel fault?  */
    if (fixup_exception(regs))
        return;

    if (handle_trapped_io(regs, address))
        return;

    /*
     * Oops. The kernel tried to access some bad page. We'll have to
     * terminate things with extreme prejudice.
     */
    bust_spinlocks(1);

    show_fault_oops(regs, address);

    die("Oops", regs, error_code);
    bust_spinlocks(0);
    do_exit(SIGKILL);
}

static void
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
               unsigned long address, int si_code)
{
    struct task_struct *tsk = current;

    /* User mode accesses just cause a SIGSEGV */
    if (user_mode(regs)) {
        /*
         * It's possible to have interrupts off here:
         */
        local_irq_enable();

        force_sig_info_fault(SIGSEGV, si_code, address, tsk);

        return;
    }

    no_context(regs, error_code, address);
}

static noinline void
bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
             unsigned long address)
{
    __bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR);
}

static void
__bad_area(struct pt_regs *regs, unsigned long error_code,
       unsigned long address, int si_code)
{
    struct mm_struct *mm = current->mm;

    /*
     * Something tried to access memory that isn't in our memory map..
     * Fix it, but check if it's kernel or user first..
     */
    up_read(&mm->mmap_sem);

    __bad_area_nosemaphore(regs, error_code, address, si_code);
}

static noinline void
bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
    __bad_area(regs, error_code, address, SEGV_MAPERR);
}

static noinline void
bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
              unsigned long address)
{
    __bad_area(regs, error_code, address, SEGV_ACCERR);
}

static void out_of_memory(void)
{
    /*
     * We ran out of memory, call the OOM killer, and return the userspace
     * (which will retry the fault, or kill us if we got oom-killed):
     */
    up_read(&current->mm->mmap_sem);

    pagefault_out_of_memory();
}

static void
do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
    struct task_struct *tsk = current;
    struct mm_struct *mm = tsk->mm;

    up_read(&mm->mmap_sem);

    /* Kernel mode? Handle exceptions or die: */
    if (!user_mode(regs))
        no_context(regs, error_code, address);

    force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
}

static noinline int
mm_fault_error(struct pt_regs *regs, unsigned long error_code,
           unsigned long address, unsigned int fault)
{
    /*
     * Pagefault was interrupted by SIGKILL. We have no reason to
     * continue pagefault.
     */
    if (fatal_signal_pending(current)) {
        if (!(fault & VM_FAULT_RETRY))
            up_read(&current->mm->mmap_sem);
        if (!user_mode(regs))
            no_context(regs, error_code, address);
        return 1;
    }

    if (!(fault & VM_FAULT_ERROR))
        return 0;

    if (fault & VM_FAULT_OOM) {
        /* Kernel mode? Handle exceptions or die: */
        if (!user_mode(regs)) {
            up_read(&current->mm->mmap_sem);
            no_context(regs, error_code, address);
            return 1;
        }

        out_of_memory();
    } else {
        if (fault & VM_FAULT_SIGBUS)
            do_sigbus(regs, error_code, address);
        else
            BUG();
    }

    return 1;
}

static inline int access_error(int error_code, struct vm_area_struct *vma)
{
    if (error_code & FAULT_CODE_WRITE) {
        /* write, present and write, not present: */
        if (unlikely(!(vma->vm_flags & VM_WRITE)))
            return 1;
        return 0;
    }

    /* ITLB miss on NX page */
    if (unlikely((error_code & FAULT_CODE_ITLB) &&
             !(vma->vm_flags & VM_EXEC)))
        return 1;

    /* read, not present: */
    if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
        return 1;

    return 0;
}

static int fault_in_kernel_space(unsigned long address)
{
    return address >= TASK_SIZE;
}

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
                    unsigned long error_code,
                    unsigned long address)
{
    unsigned long vec;
    struct task_struct *tsk;
    struct mm_struct *mm;
    struct vm_area_struct * vma;
    int fault;
    int write = error_code & FAULT_CODE_WRITE;
    unsigned int flags = (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
                  (write ? FAULT_FLAG_WRITE : 0));

    tsk = current;
    mm = tsk->mm;
    vec = lookup_exception_vector();

    /*
     * 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 (unlikely(fault_in_kernel_space(address))) {
        if (vmalloc_fault(address) >= 0)
            return;
        if (notify_page_fault(regs, vec))
            return;

        bad_area_nosemaphore(regs, error_code, address);
        return;
    }

    if (unlikely(notify_page_fault(regs, vec)))
        return;

    /* Only enable interrupts if they were on before the fault */
    if ((regs->sr & SR_IMASK) != SR_IMASK)
        local_irq_enable();

    perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

    /*
     * If we're in an interrupt, have no user context or are running
     * in an atomic region then we must not take the fault:
     */
    if (unlikely(in_atomic() || !mm)) {
        bad_area_nosemaphore(regs, error_code, address);
        return;
    }

retry:
    down_read(&mm->mmap_sem);

    vma = find_vma(mm, address);
    if (unlikely(!vma)) {
        bad_area(regs, error_code, address);
        return;
    }
    if (likely(vma->vm_start <= address))
        goto good_area;
    if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
        bad_area(regs, error_code, address);
        return;
    }
    if (unlikely(expand_stack(vma, address))) {
        bad_area(regs, error_code, address);
        return;
    }

    /*
     * Ok, we have a good vm_area for this memory access, so
     * we can handle it..
     */
good_area:
    if (unlikely(access_error(error_code, vma))) {
        bad_area_access_error(regs, error_code, address);
        return;
    }

    set_thread_fault_code(error_code);

    /*
     * 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 (unlikely(fault & (VM_FAULT_RETRY | VM_FAULT_ERROR)))
        if (mm_fault_error(regs, error_code, address, fault))
            return;

    if (flags & FAULT_FLAG_ALLOW_RETRY) {
        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;

            /*
             * 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);
}