s390/pfault: fix task state race

[linux/fpc-iii.git] / arch / s390 / mm / fault.c

/*
 *  arch/s390/mm/fault.c
 *
 *  S390 version
 *    Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
 *    Author(s): Hartmut Penner (hp@de.ibm.com)
 *               Ulrich Weigand (uweigand@de.ibm.com)
 *
 *  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/system.h>
#include <asm/pgtable.h>
#include <asm/irq.h>
#include <asm/mmu_context.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

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 (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 = 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 (regs->psw.mask & PSW_MASK_PSTATE) {
                        /* 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;
        default: /* fault & VM_FAULT_ERROR */
                if (fault & VM_FAULT_OOM) {
                        if (!(regs->psw.mask & PSW_MASK_PSTATE))
                                do_no_context(regs);
                        else
                                pagefault_out_of_memory();
                } else if (fault & VM_FAULT_SIGBUS) {
                        /* Kernel mode? Handle exceptions or die */
                        if (!(regs->psw.mask & PSW_MASK_PSTATE))
                                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;
        if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
                flags |= FAULT_FLAG_WRITE;
        down_read(&mm->mmap_sem);

#ifdef CONFIG_PGSTE
        if (test_tsk_thread_flag(current, TIF_SIE) && 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);
        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;
                        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 (regs->psw.mask & PSW_MASK_PSTATE) {
                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;

        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);
        if (unlikely(fault)) {
                if (fault & VM_FAULT_OOM)
                        return -EFAULT;
                else if (fault & VM_FAULT_SIGBUS)
                        do_sigbus(&regs);
        }
        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(unsigned int ext_int_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_int_code >> 16;
        if ((subcode & 0xff00) != __SUBCODE_MASK)
                return;
        kstat_cpu(smp_processor_id()).irqs[EXTINT_PFL]++;
        if (subcode & 0x0080) {
                /* 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;
        } else {
                tsk = current;
        }
        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;
                }
                put_task_struct(tsk);
        } else {
                /* signal bit not set -> a real page is missing. */
                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);
                }
        }
        spin_unlock(&pfault_lock);
}

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) {
        case CPU_DEAD:
        case CPU_DEAD_FROZEN:
                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 */