/*
 *  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/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/smp.h>
#include <linux/kdebug.h>
#include <linux/smp_lock.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/system.h>
#include <asm/pgtable.h>
#include <asm/s390_ext.h>
#include <asm/mmu_context.h>
#include "../kernel/entry.h"

#ifndef CONFIG_64BIT
#define __FAIL_ADDR_MASK 0x7ffff000
#define __FIXUP_MASK 0x7fffffff
#define __SUBCODE_MASK 0x0200
#define __PF_RES_FIELD 0ULL
#else /* CONFIG_64BIT */
#define __FAIL_ADDR_MASK -4096L
#define __FIXUP_MASK ~0L
#define __SUBCODE_MASK 0x0600
#define __PF_RES_FIELD 0x8000000000000000ULL
#endif /* CONFIG_64BIT */

#ifdef CONFIG_SYSCTL
extern int sysctl_userprocess_debug;
#endif

#ifdef CONFIG_KPROBES
static inline int notify_page_fault(struct pt_regs *regs, long err)
{
        int ret = 0;

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

        return ret;
}
#else
static inline int notify_page_fault(struct pt_regs *regs, long err)
{
        return 0;
}
#endif


/*
 * 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, 1 for user space and
 * 2 for code execution in user space with noexec=on.
 */
static inline int check_space(struct task_struct *tsk)
{
        /*
         * The lowest two bits of S390_lowcore.trans_exc_code
         * indicate which paging table was used.
         */
        int desc = S390_lowcore.trans_exc_code & 3;

        if (desc == 3)  /* Home Segment Table Descriptor */
                return switch_amode == 0;
        if (desc == 2)  /* Secondary Segment Table Descriptor */
                return tsk->thread.mm_segment.ar4;
#ifdef CONFIG_S390_SWITCH_AMODE
        if (unlikely(desc == 1)) { /* STD determined via access register */
                /* %a0 always indicates primary space. */
                if (S390_lowcore.exc_access_id != 0) {
                        save_access_regs(tsk->thread.acrs);
                        /*
                         * An alet of 0 indicates primary space.
                         * An alet of 1 indicates secondary space.
                         * Any other alet values generate an
                         * alen-translation exception.
                         */
                        if (tsk->thread.acrs[S390_lowcore.exc_access_id])
                                return tsk->thread.mm_segment.ar4;
                }
        }
#endif
        /* Primary Segment Table Descriptor */
        return switch_amode << s390_noexec;
}

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

#if defined(CONFIG_SYSCTL) || defined(CONFIG_PROCESS_DEBUG)
#if defined(CONFIG_SYSCTL)
        if (sysctl_userprocess_debug)
#endif
        {
                printk("User process fault: interruption code 0x%lX\n",
                       error_code);
                printk("failing address: %lX\n", address);
                show_regs(regs);
        }
#endif
        si.si_signo = SIGSEGV;
        si.si_code = si_code;
        si.si_addr = (void __user *) address;
        force_sig_info(SIGSEGV, &si, current);
}

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

        /* Are we prepared to handle this kernel fault?  */
        fixup = search_exception_tables(regs->psw.addr & __FIXUP_MASK);
        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.
         */
        if (check_space(current) == 0)
                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("Oops", regs, error_code);
        do_exit(SIGKILL);
}

static void do_low_address(struct pt_regs *regs, unsigned long error_code)
{
        /* 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 ("Low-address protection", regs, error_code);
                do_exit(SIGKILL);
        }

        do_no_context(regs, error_code, 0);
}

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
static int do_out_of_memory(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);
        if (is_global_init(tsk)) {
                yield();
                down_read(&mm->mmap_sem);
                return 1;
        }
        printk("VM: killing process %s\n", tsk->comm);
        if (regs->psw.mask & PSW_MASK_PSTATE)
                do_group_exit(SIGKILL);
        do_no_context(regs, error_code, address);
        return 0;
}

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);
        /*
         * Send a sigbus, regardless of whether we were in kernel
         * or user mode.
         */
        tsk->thread.prot_addr = address;
        tsk->thread.trap_no = error_code;
        force_sig(SIGBUS, tsk);

        /* Kernel mode? Handle exceptions or die */
        if (!(regs->psw.mask & PSW_MASK_PSTATE))
                do_no_context(regs, error_code, address);
}

#ifdef CONFIG_S390_EXEC_PROTECT
static int signal_return(struct mm_struct *mm, struct pt_regs *regs,
                         unsigned long address, unsigned long error_code)
{
        u16 instruction;
        int rc;
#ifdef CONFIG_COMPAT
        int compat;
#endif

        pagefault_disable();
        rc = __get_user(instruction, (u16 __user *) regs->psw.addr);
        pagefault_enable();
        if (rc)
                return -EFAULT;

        up_read(&mm->mmap_sem);
        clear_tsk_thread_flag(current, TIF_SINGLE_STEP);
#ifdef CONFIG_COMPAT
        compat = test_tsk_thread_flag(current, TIF_31BIT);
        if (compat && instruction == 0x0a77)
                sys32_sigreturn();
        else if (compat && instruction == 0x0aad)
                sys32_rt_sigreturn();
        else
#endif
        if (instruction == 0x0a77)
                sys_sigreturn();
        else if (instruction == 0x0aad)
                sys_rt_sigreturn();
        else {
                current->thread.prot_addr = address;
                current->thread.trap_no = error_code;
                do_sigsegv(regs, error_code, SEGV_MAPERR, address);
        }
        return 0;
}
#endif /* CONFIG_S390_EXEC_PROTECT */

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * error_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 void
do_exception(struct pt_regs *regs, unsigned long error_code, int write)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct *vma;
        unsigned long address;
        int space;
        int si_code;
        int fault;

        if (notify_page_fault(regs, error_code))
                return;

        tsk = current;
        mm = tsk->mm;

        /* get the failing address and the affected space */
        address = S390_lowcore.trans_exc_code & __FAIL_ADDR_MASK;
        space = check_space(tsk);

        /*
         * Verify that the fault happened in user space, that
         * we are not in an interrupt and that there is a 
         * user context.
         */
        if (unlikely(space == 0 || in_atomic() || !mm))
                goto no_context;

        /*
         * When we get here, the fault happened in the current
         * task's user address space, so we can switch on the
         * interrupts again and then search the VMAs
         */
        local_irq_enable();

        down_read(&mm->mmap_sem);

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

#ifdef CONFIG_S390_EXEC_PROTECT
        if (unlikely((space == 2) && !(vma->vm_flags & VM_EXEC)))
                if (!signal_return(mm, regs, address, error_code))
                        /*
                         * signal_return() has done an up_read(&mm->mmap_sem)
                         * if it returns 0.
                         */
                        return;
#endif

        if (vma->vm_start <= address)
                goto good_area;
        if (!(vma->vm_flags & VM_GROWSDOWN))
                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:
        si_code = SEGV_ACCERR;
        if (!write) {
                /* page not present, check vm flags */
                if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                        goto bad_area;
        } else {
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
        }

survive:
        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, write);
        if (unlikely(fault & VM_FAULT_ERROR)) {
                if (fault & VM_FAULT_OOM) {
                        if (do_out_of_memory(regs, error_code, address))
                                goto survive;
                        return;
                } else if (fault & VM_FAULT_SIGBUS) {
                        do_sigbus(regs, error_code, address);
                        return;
                }
                BUG();
        }
        if (fault & VM_FAULT_MAJOR)
                tsk->maj_flt++;
        else
                tsk->min_flt++;

        up_read(&mm->mmap_sem);
        /*
         * The instruction that caused the program check will
         * be repeated. Don't signal single step via SIGTRAP.
         */
        clear_tsk_thread_flag(tsk, TIF_SINGLE_STEP);
        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);

        /* User mode accesses just cause a SIGSEGV */
        if (regs->psw.mask & PSW_MASK_PSTATE) {
                tsk->thread.prot_addr = address;
                tsk->thread.trap_no = error_code;
                do_sigsegv(regs, error_code, si_code, address);
                return;
        }

no_context:
        do_no_context(regs, error_code, address);
}

void __kprobes do_protection_exception(struct pt_regs *regs,
                                       long error_code)
{
        /* Protection exception is supressing, decrement psw address. */
        regs->psw.addr -= (error_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(!(S390_lowcore.trans_exc_code & 4))) {
                do_low_address(regs, error_code);
                return;
        }
        do_exception(regs, 4, 1);
}

void __kprobes do_dat_exception(struct pt_regs *regs, long error_code)
{
        do_exception(regs, error_code & 0xff, 0);
}

#ifdef CONFIG_64BIT
void __kprobes do_asce_exception(struct pt_regs *regs, unsigned long error_code)
{
        struct mm_struct *mm;
        struct vm_area_struct *vma;
        unsigned long address;
        int space;

        mm = current->mm;
        address = S390_lowcore.trans_exc_code & __FAIL_ADDR_MASK;
        space = check_space(current);

        if (unlikely(space == 0 || in_atomic() || !mm))
                goto no_context;

        local_irq_enable();

        down_read(&mm->mmap_sem);
        vma = find_vma(mm, address);
        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) {
                current->thread.prot_addr = address;
                current->thread.trap_no = error_code;
                do_sigsegv(regs, error_code, SEGV_MAPERR, address);
                return;
        }

no_context:
        do_no_context(regs, error_code, address);
}
#endif

#ifdef CONFIG_PFAULT 
/*
 * 'pfault' pseudo page faults routines.
 */
static ext_int_info_t ext_int_pfault;
static int pfault_disable = 0;

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

__setup("nopfault", nopfault);

typedef struct {
        __u16 refdiagc;
        __u16 reffcode;
        __u16 refdwlen;
        __u16 refversn;
        __u64 refgaddr;
        __u64 refselmk;
        __u64 refcmpmk;
        __u64 reserved;
} __attribute__ ((packed, aligned(8))) pfault_refbk_t;

int pfault_init(void)
{
        pfault_refbk_t refbk =
                { 0x258, 0, 5, 2, __LC_CURRENT, 1ULL << 48, 1ULL << 48,
                  __PF_RES_FIELD };
        int rc;

        if (!MACHINE_IS_VM || 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");
        __ctl_set_bit(0, 9);
        return rc;
}

void pfault_fini(void)
{
        pfault_refbk_t refbk =
        { 0x258, 1, 5, 2, 0ULL, 0ULL, 0ULL, 0ULL };

        if (!MACHINE_IS_VM || pfault_disable)
                return;
        __ctl_clear_bit(0,9);
        asm volatile(
                "       diag    %0,0,0x258\n"
                "0:\n"
                EX_TABLE(0b,0b)
                : : "a" (&refbk), "m" (refbk) : "cc");
}

static void pfault_interrupt(__u16 error_code)
{
        struct task_struct *tsk;
        __u16 subcode;

        /*
         * Get the external interruption subcode & pfault
         * initial/completion signal bit. VM stores this 
         * in the 'cpu address' field associated with the
         * external interrupt. 
         */
        subcode = S390_lowcore.cpu_addr;
        if ((subcode & 0xff00) != __SUBCODE_MASK)
                return;

        /*
         * Get the token (= address of the task structure of the affected task).
         */
        tsk = *(struct task_struct **) __LC_PFAULT_INTPARM;

        if (subcode & 0x0080) {
                /* signal bit is set -> a page has been swapped in by VM */
                if (xchg(&tsk->thread.pfault_wait, -1) != 0) {
                        /* 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;
                        wake_up_process(tsk);
                        put_task_struct(tsk);
                }
        } else {
                /* signal bit not set -> a real page is missing. */
                get_task_struct(tsk);
                set_task_state(tsk, TASK_UNINTERRUPTIBLE);
                if (xchg(&tsk->thread.pfault_wait, 1) != 0) {
                        /* Completion interrupt was faster than the initial
                         * interrupt (swapped in a -1 for pfault_wait). Set
                         * pfault_wait back to zero and exit. This can be
                         * done safely because tsk is running in kernel 
                         * mode and can't produce new pfaults. */
                        tsk->thread.pfault_wait = 0;
                        set_task_state(tsk, TASK_RUNNING);
                        put_task_struct(tsk);
                } else
                        set_tsk_need_resched(tsk);
        }
}

void __init pfault_irq_init(void)
{
        if (!MACHINE_IS_VM)
                return;

        /*
         * Try to get pfault pseudo page faults going.
         */
        if (register_early_external_interrupt(0x2603, pfault_interrupt,
                                              &ext_int_pfault) != 0)
                panic("Couldn't request external interrupt 0x2603");

        if (pfault_init() == 0)
                return;

        /* Tough luck, no pfault. */
        pfault_disable = 1;
        unregister_early_external_interrupt(0x2603, pfault_interrupt,
                                            &ext_int_pfault);
}
#endif