arch/s390/mm/fault.c - kernel/msm - Gitiles

 /*
  *  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
	/*
	* 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