fault.c

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/*
 *  S390 version
 *    Copyright IBM Corp. 1999
 *    Author(s): Hartmut Penner ([email protected])
 *               Ulrich Weigand ([email protected])
 *
 *  Derived from "arch/i386/mm/fault.c"
 *    Copyright (C) 1995  Linus Torvalds
 */

#include <linux/kernel_stat.h>
#include <linux/perf_event.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/compat.h>
#include <linux/smp.h>
#include <linux/kdebug.h>
#include <linux/init.h>
#include <linux/console.h>
#include <linux/module.h>
#include <linux/hardirq.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/hugetlb.h>
#include <asm/asm-offsets.h>
#include <asm/pgtable.h>
#include <asm/irq.h>
#include <asm/mmu_context.h>
#include <asm/facility.h>
#include "../kernel/entry.h"

#ifndef CONFIG_64BIT
#define __FAIL_ADDR_MASK 0x7ffff000
#define __SUBCODE_MASK 0x0200
#define __PF_RES_FIELD 0ULL
#else /* CONFIG_64BIT */
#define __FAIL_ADDR_MASK -4096L
#define __SUBCODE_MASK 0x0600
#define __PF_RES_FIELD 0x8000000000000000ULL
#endif /* CONFIG_64BIT */

#define VM_FAULT_BADCONTEXT 0x010000
#define VM_FAULT_BADMAP     0x020000
#define VM_FAULT_BADACCESS  0x040000
#define VM_FAULT_SIGNAL 0x080000

static unsigned long store_indication;

void fault_init(void)
{
    if (test_facility(2) && test_facility(75))
        store_indication = 0xc00;
}

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

    /* kprobe_running() needs smp_processor_id() */
    if (kprobes_built_in() && !user_mode(regs)) {
        preempt_disable();
        if (kprobe_running() && kprobe_fault_handler(regs, 14))
            ret = 1;
        preempt_enable();
    }
    return ret;
}


/*
 * Unlock any spinlocks which will prevent us from getting the
 * message out.
 */
void bust_spinlocks(int yes)
{
    if (yes) {
        oops_in_progress = 1;
    } else {
        int loglevel_save = console_loglevel;
        console_unblank();
        oops_in_progress = 0;
        /*
         * OK, the message is on the console.  Now we call printk()
         * without oops_in_progress set so that printk will give klogd
         * a poke.  Hold onto your hats...
         */
        console_loglevel = 15;
        printk(" ");
        console_loglevel = loglevel_save;
    }
}

/*
 * Returns the address space associated with the fault.
 * Returns 0 for kernel space and 1 for user space.
 */
static inline int user_space_fault(unsigned long trans_exc_code)
{
    /*
     * The lowest two bits of the translation exception
     * identification indicate which paging table was used.
     */
    trans_exc_code &= 3;
    if (trans_exc_code == 2)
        /* Access via secondary space, set_fs setting decides */
        return current->thread.mm_segment.ar4;
    if (s390_user_mode == HOME_SPACE_MODE)
        /* User space if the access has been done via home space. */
        return trans_exc_code == 3;
    /*
     * If the user space is not the home space the kernel runs in home
     * space. Access via secondary space has already been covered,
     * access via primary space or access register is from user space
     * and access via home space is from the kernel.
     */
    return trans_exc_code != 3;
}

static inline void report_user_fault(struct pt_regs *regs, long signr)
{
    if ((task_pid_nr(current) > 1) && !show_unhandled_signals)
        return;
    if (!unhandled_signal(current, signr))
        return;
    if (!printk_ratelimit())
        return;
    printk(KERN_ALERT "User process fault: interruption code 0x%X ",
           regs->int_code);
    print_vma_addr(KERN_CONT "in ", regs->psw.addr & PSW_ADDR_INSN);
    printk(KERN_CONT "\n");
    printk(KERN_ALERT "failing address: %lX\n",
           regs->int_parm_long & __FAIL_ADDR_MASK);
    show_regs(regs);
}

/*
 * Send SIGSEGV to task.  This is an external routine
 * to keep the stack usage of do_page_fault small.
 */
static noinline void do_sigsegv(struct pt_regs *regs, int si_code)
{
    struct siginfo si;

    report_user_fault(regs, SIGSEGV);
    si.si_signo = SIGSEGV;
    si.si_code = si_code;
    si.si_addr = (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK);
    force_sig_info(SIGSEGV, &si, current);
}

static noinline void do_no_context(struct pt_regs *regs)
{
    const struct exception_table_entry *fixup;
    unsigned long address;

    /* Are we prepared to handle this kernel fault?  */
    fixup = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
    if (fixup) {
        regs->psw.addr = extable_fixup(fixup) | PSW_ADDR_AMODE;
        return;
    }

    /*
     * Oops. The kernel tried to access some bad page. We'll have to
     * terminate things with extreme prejudice.
     */
    address = regs->int_parm_long & __FAIL_ADDR_MASK;
    if (!user_space_fault(regs->int_parm_long))
        printk(KERN_ALERT "Unable to handle kernel pointer dereference"
               " at virtual kernel address %p\n", (void *)address);
    else
        printk(KERN_ALERT "Unable to handle kernel paging request"
               " at virtual user address %p\n", (void *)address);

    die(regs, "Oops");
    do_exit(SIGKILL);
}

static noinline void do_low_address(struct pt_regs *regs)
{
    /* Low-address protection hit in kernel mode means
       NULL pointer write access in kernel mode.  */
    if (regs->psw.mask & PSW_MASK_PSTATE) {
        /* Low-address protection hit in user mode 'cannot happen'. */
        die (regs, "Low-address protection");
        do_exit(SIGKILL);
    }

    do_no_context(regs);
}

static noinline void do_sigbus(struct pt_regs *regs)
{
    struct task_struct *tsk = current;
    struct siginfo si;

    /*
     * Send a sigbus, regardless of whether we were in kernel
     * or user mode.
     */
    si.si_signo = SIGBUS;
    si.si_errno = 0;
    si.si_code = BUS_ADRERR;
    si.si_addr = (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK);
    force_sig_info(SIGBUS, &si, tsk);
}

static noinline void do_fault_error(struct pt_regs *regs, int fault)
{
    int si_code;

    switch (fault) {
    case VM_FAULT_BADACCESS:
    case VM_FAULT_BADMAP:
        /* Bad memory access. Check if it is kernel or user space. */
        if (user_mode(regs)) {
            /* User mode accesses just cause a SIGSEGV */
            si_code = (fault == VM_FAULT_BADMAP) ?
                SEGV_MAPERR : SEGV_ACCERR;
            do_sigsegv(regs, si_code);
            return;
        }
    case VM_FAULT_BADCONTEXT:
        do_no_context(regs);
        break;
    case VM_FAULT_SIGNAL:
        if (!user_mode(regs))
            do_no_context(regs);
        break;
    default: /* fault & VM_FAULT_ERROR */
        if (fault & VM_FAULT_OOM) {
            if (!user_mode(regs))
                do_no_context(regs);
            else
                pagefault_out_of_memory();
        } else if (fault & VM_FAULT_SIGBUS) {
            /* Kernel mode? Handle exceptions or die */
            if (!user_mode(regs))
                do_no_context(regs);
            else
                do_sigbus(regs);
        } else
            BUG();
        break;
    }
}

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * interruption code (int_code):
 *   04       Protection           ->  Write-Protection  (suprression)
 *   10       Segment translation  ->  Not present       (nullification)
 *   11       Page translation     ->  Not present       (nullification)
 *   3b       Region third trans.  ->  Not present       (nullification)
 */
static inline int do_exception(struct pt_regs *regs, int access)
{
    struct task_struct *tsk;
    struct mm_struct *mm;
    struct vm_area_struct *vma;
    unsigned long trans_exc_code;
    unsigned long address;
    unsigned int flags;
    int fault;

    if (notify_page_fault(regs))
        return 0;

    tsk = current;
    mm = tsk->mm;
    trans_exc_code = regs->int_parm_long;

    /*
     * Verify that the fault happened in user space, that
     * we are not in an interrupt and that there is a 
     * user context.
     */
    fault = VM_FAULT_BADCONTEXT;
    if (unlikely(!user_space_fault(trans_exc_code) || in_atomic() || !mm))
        goto out;

    address = trans_exc_code & __FAIL_ADDR_MASK;
    perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
    flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
    if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
        flags |= FAULT_FLAG_WRITE;
    down_read(&mm->mmap_sem);

#ifdef CONFIG_PGSTE
    if ((current->flags & PF_VCPU) && S390_lowcore.gmap) {
        address = __gmap_fault(address,
                     (struct gmap *) S390_lowcore.gmap);
        if (address == -EFAULT) {
            fault = VM_FAULT_BADMAP;
            goto out_up;
        }
        if (address == -ENOMEM) {
            fault = VM_FAULT_OOM;
            goto out_up;
        }
    }
#endif

retry:
    fault = VM_FAULT_BADMAP;
    vma = find_vma(mm, address);
    if (!vma)
        goto out_up;

    if (unlikely(vma->vm_start > address)) {
        if (!(vma->vm_flags & VM_GROWSDOWN))
            goto out_up;
        if (expand_stack(vma, address))
            goto out_up;
    }

    /*
     * Ok, we have a good vm_area for this memory access, so
     * we can handle it..
     */
    fault = VM_FAULT_BADACCESS;
    if (unlikely(!(vma->vm_flags & access)))
        goto out_up;

    if (is_vm_hugetlb_page(vma))
        address &= HPAGE_MASK;
    /*
     * 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);
    /* No reason to continue if interrupted by SIGKILL. */
    if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
        fault = VM_FAULT_SIGNAL;
        goto out;
    }
    if (unlikely(fault & VM_FAULT_ERROR))
        goto out_up;

    /*
     * Major/minor page fault accounting is only done on the
     * initial attempt. If we go through a retry, it is extremely
     * likely that the page will be found in page cache at that point.
     */
    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) {
            /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
             * of starvation. */
            flags &= ~FAULT_FLAG_ALLOW_RETRY;
            flags |= FAULT_FLAG_TRIED;
            down_read(&mm->mmap_sem);
            goto retry;
        }
    }
    /*
     * The instruction that caused the program check will
     * be repeated. Don't signal single step via SIGTRAP.
     */
    clear_tsk_thread_flag(tsk, TIF_PER_TRAP);
    fault = 0;
out_up:
    up_read(&mm->mmap_sem);
out:
    return fault;
}

void __kprobes do_protection_exception(struct pt_regs *regs)
{
    unsigned long trans_exc_code;
    int fault;

    trans_exc_code = regs->int_parm_long;
    /* Protection exception is suppressing, decrement psw address. */
    regs->psw.addr = __rewind_psw(regs->psw, regs->int_code >> 16);
    /*
     * Check for low-address protection.  This needs to be treated
     * as a special case because the translation exception code
     * field is not guaranteed to contain valid data in this case.
     */
    if (unlikely(!(trans_exc_code & 4))) {
        do_low_address(regs);
        return;
    }
    fault = do_exception(regs, VM_WRITE);
    if (unlikely(fault))
        do_fault_error(regs, fault);
}

void __kprobes do_dat_exception(struct pt_regs *regs)
{
    int access, fault;

    access = VM_READ | VM_EXEC | VM_WRITE;
    fault = do_exception(regs, access);
    if (unlikely(fault))
        do_fault_error(regs, fault);
}

#ifdef CONFIG_64BIT
void __kprobes do_asce_exception(struct pt_regs *regs)
{
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma;
    unsigned long trans_exc_code;

    trans_exc_code = regs->int_parm_long;
    if (unlikely(!user_space_fault(trans_exc_code) || in_atomic() || !mm))
        goto no_context;

    down_read(&mm->mmap_sem);
    vma = find_vma(mm, trans_exc_code & __FAIL_ADDR_MASK);
    up_read(&mm->mmap_sem);

    if (vma) {
        update_mm(mm, current);
        return;
    }

    /* User mode accesses just cause a SIGSEGV */
    if (user_mode(regs)) {
        do_sigsegv(regs, SEGV_MAPERR);
        return;
    }

no_context:
    do_no_context(regs);
}
#endif

int __handle_fault(unsigned long uaddr, unsigned long pgm_int_code, int write)
{
    struct pt_regs regs;
    int access, fault;

    /* Emulate a uaccess fault from kernel mode. */
    regs.psw.mask = psw_kernel_bits | PSW_MASK_DAT | PSW_MASK_MCHECK;
    if (!irqs_disabled())
        regs.psw.mask |= PSW_MASK_IO | PSW_MASK_EXT;
    regs.psw.addr = (unsigned long) __builtin_return_address(0);
    regs.psw.addr |= PSW_ADDR_AMODE;
    regs.int_code = pgm_int_code;
    regs.int_parm_long = (uaddr & PAGE_MASK) | 2;
    access = write ? VM_WRITE : VM_READ;
    fault = do_exception(&regs, access);
    /*
     * Since the fault happened in kernel mode while performing a uaccess
     * all we need to do now is emulating a fixup in case "fault" is not
     * zero.
     * For the calling uaccess functions this results always in -EFAULT.
     */
    return fault ? -EFAULT : 0;
}

#ifdef CONFIG_PFAULT 
/*
 * 'pfault' pseudo page faults routines.
 */
static int pfault_disable;

static int __init nopfault(char *str)
{
    pfault_disable = 1;
    return 1;
}

__setup("nopfault", nopfault);

struct pfault_refbk {
    u16 refdiagc;
    u16 reffcode;
    u16 refdwlen;
    u16 refversn;
    u64 refgaddr;
    u64 refselmk;
    u64 refcmpmk;
    u64 reserved;
} __attribute__ ((packed, aligned(8)));

int pfault_init(void)
{
    struct pfault_refbk refbk = {
        .refdiagc = 0x258,
        .reffcode = 0,
        .refdwlen = 5,
        .refversn = 2,
        .refgaddr = __LC_CURRENT_PID,
        .refselmk = 1ULL << 48,
        .refcmpmk = 1ULL << 48,
        .reserved = __PF_RES_FIELD };
        int rc;

    if (pfault_disable)
        return -1;
    asm volatile(
        "   diag    %1,%0,0x258\n"
        "0: j   2f\n"
        "1: la  %0,8\n"
        "2:\n"
        EX_TABLE(0b,1b)
        : "=d" (rc) : "a" (&refbk), "m" (refbk) : "cc");
        return rc;
}

void pfault_fini(void)
{
    struct pfault_refbk refbk = {
        .refdiagc = 0x258,
        .reffcode = 1,
        .refdwlen = 5,
        .refversn = 2,
    };

    if (pfault_disable)
        return;
    asm volatile(
        "   diag    %0,0,0x258\n"
        "0:\n"
        EX_TABLE(0b,0b)
        : : "a" (&refbk), "m" (refbk) : "cc");
}

static DEFINE_SPINLOCK(pfault_lock);
static LIST_HEAD(pfault_list);

static void pfault_interrupt(struct ext_code ext_code,
                 unsigned int param32, unsigned long param64)
{
    struct task_struct *tsk;
    __u16 subcode;
    pid_t pid;

    /*
     * Get the external interruption subcode & pfault
     * initial/completion signal bit. VM stores this 
     * in the 'cpu address' field associated with the
         * external interrupt. 
     */
    subcode = ext_code.subcode;
    if ((subcode & 0xff00) != __SUBCODE_MASK)
        return;
    kstat_cpu(smp_processor_id()).irqs[EXTINT_PFL]++;
    /* Get the token (= pid of the affected task). */
    pid = sizeof(void *) == 4 ? param32 : param64;
    rcu_read_lock();
    tsk = find_task_by_pid_ns(pid, &init_pid_ns);
    if (tsk)
        get_task_struct(tsk);
    rcu_read_unlock();
    if (!tsk)
        return;
    spin_lock(&pfault_lock);
    if (subcode & 0x0080) {
        /* signal bit is set -> a page has been swapped in by VM */
        if (tsk->thread.pfault_wait == 1) {
            /* Initial interrupt was faster than the completion
             * interrupt. pfault_wait is valid. Set pfault_wait
             * back to zero and wake up the process. This can
             * safely be done because the task is still sleeping
             * and can't produce new pfaults. */
            tsk->thread.pfault_wait = 0;
            list_del(&tsk->thread.list);
            wake_up_process(tsk);
            put_task_struct(tsk);
        } else {
            /* Completion interrupt was faster than initial
             * interrupt. Set pfault_wait to -1 so the initial
             * interrupt doesn't put the task to sleep.
             * If the task is not running, ignore the completion
             * interrupt since it must be a leftover of a PFAULT
             * CANCEL operation which didn't remove all pending
             * completion interrupts. */
            if (tsk->state == TASK_RUNNING)
                tsk->thread.pfault_wait = -1;
        }
    } else {
        /* signal bit not set -> a real page is missing. */
        if (WARN_ON_ONCE(tsk != current))
            goto out;
        if (tsk->thread.pfault_wait == 1) {
            /* Already on the list with a reference: put to sleep */
            __set_task_state(tsk, TASK_UNINTERRUPTIBLE);
            set_tsk_need_resched(tsk);
        } else if (tsk->thread.pfault_wait == -1) {
            /* Completion interrupt was faster than the initial
             * interrupt (pfault_wait == -1). Set pfault_wait
             * back to zero and exit. */
            tsk->thread.pfault_wait = 0;
        } else {
            /* Initial interrupt arrived before completion
             * interrupt. Let the task sleep.
             * An extra task reference is needed since a different
             * cpu may set the task state to TASK_RUNNING again
             * before the scheduler is reached. */
            get_task_struct(tsk);
            tsk->thread.pfault_wait = 1;
            list_add(&tsk->thread.list, &pfault_list);
            __set_task_state(tsk, TASK_UNINTERRUPTIBLE);
            set_tsk_need_resched(tsk);
        }
    }
out:
    spin_unlock(&pfault_lock);
    put_task_struct(tsk);
}

static int __cpuinit pfault_cpu_notify(struct notifier_block *self,
                       unsigned long action, void *hcpu)
{
    struct thread_struct *thread, *next;
    struct task_struct *tsk;

    switch (action & ~CPU_TASKS_FROZEN) {
    case CPU_DEAD:
        spin_lock_irq(&pfault_lock);
        list_for_each_entry_safe(thread, next, &pfault_list, list) {
            thread->pfault_wait = 0;
            list_del(&thread->list);
            tsk = container_of(thread, struct task_struct, thread);
            wake_up_process(tsk);
            put_task_struct(tsk);
        }
        spin_unlock_irq(&pfault_lock);
        break;
    default:
        break;
    }
    return NOTIFY_OK;
}

static int __init pfault_irq_init(void)
{
    int rc;

    rc = register_external_interrupt(0x2603, pfault_interrupt);
    if (rc)
        goto out_extint;
    rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
    if (rc)
        goto out_pfault;
    service_subclass_irq_register();
    hotcpu_notifier(pfault_cpu_notify, 0);
    return 0;

out_pfault:
    unregister_external_interrupt(0x2603, pfault_interrupt);
out_extint:
    pfault_disable = 1;
    return rc;
}
early_initcall(pfault_irq_init);

#endif /* CONFIG_PFAULT */