arch/s390/mm/fault.c - third_party/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  *  S390 version
  *    Copyright IBM Corp. 1999
  *    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/sched/debug.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/extable.h>
 #include <linux/hardirq.h>
 #include <linux/kprobes.h>
 #include <linux/uaccess.h>
 #include <linux/hugetlb.h>
 #include <asm/asm-offsets.h>
 #include <asm/diag.h>
 #include <asm/pgtable.h>
 #include <asm/gmap.h>
 #include <asm/irq.h>
 #include <asm/mmu_context.h>
 #include <asm/facility.h>
 #include "../kernel/entry.h"

 #define __FAIL_ADDR_MASK -4096L
 #define __SUBCODE_MASK 0x0600
 #define __PF_RES_FIELD 0x8000000000000000ULL

 #define VM_FAULT_BADCONTEXT	0x010000
 #define VM_FAULT_BADMAP		0x020000
 #define VM_FAULT_BADACCESS	0x040000
 #define VM_FAULT_SIGNAL		0x080000
 #define VM_FAULT_PFAULT		0x100000

 enum fault_type {
 	KERNEL_FAULT,
 	USER_FAULT,
 	VDSO_FAULT,
 	GMAP_FAULT,
 };

 static unsigned long store_indication __read_mostly;

 static int __init fault_init(void)
 {
 	if (test_facility(75))
 		store_indication = 0xc00;
 	return 0;
 }
 early_initcall(fault_init);

 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;
 	}
 }

 /*
  * Find out which address space caused the exception.
  * Access register mode is impossible, ignore space == 3.
  */
 static inline enum fault_type get_fault_type(struct pt_regs *regs)
 {
 	unsigned long trans_exc_code;

 	trans_exc_code = regs->int_parm_long & 3;
 	if (likely(trans_exc_code == 0)) {
 		/* primary space exception */
 		if (IS_ENABLED(CONFIG_PGSTE) &&
 		    test_pt_regs_flag(regs, PIF_GUEST_FAULT))
 			return GMAP_FAULT;
 		if (current->thread.mm_segment == USER_DS)
 			return USER_FAULT;
 		return KERNEL_FAULT;
 	}
 	if (trans_exc_code == 2) {
 		/* secondary space exception */
 		if (current->thread.mm_segment & 1) {
 			if (current->thread.mm_segment == USER_DS_SACF)
 				return USER_FAULT;
 			return KERNEL_FAULT;
 		}
 		return VDSO_FAULT;
 	}
 	/* home space exception -> access via kernel ASCE */
 	return KERNEL_FAULT;
 }

 static int bad_address(void *p)
 {
 	unsigned long dummy;

 	return probe_kernel_address((unsigned long *)p, dummy);
 }

 static void dump_pagetable(unsigned long asce, unsigned long address)
 {
 	unsigned long *table = __va(asce & _ASCE_ORIGIN);

 	pr_alert("AS:%016lx ", asce);
 	switch (asce & _ASCE_TYPE_MASK) {
 	case _ASCE_TYPE_REGION1:
 		table += (address & _REGION1_INDEX) >> _REGION1_SHIFT;
 		if (bad_address(table))
 			goto bad;
 		pr_cont("R1:%016lx ", *table);
 		if (*table & _REGION_ENTRY_INVALID)
 			goto out;
 		table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
 		/* fallthrough */
 	case _ASCE_TYPE_REGION2:
 		table += (address & _REGION2_INDEX) >> _REGION2_SHIFT;
 		if (bad_address(table))
 			goto bad;
 		pr_cont("R2:%016lx ", *table);
 		if (*table & _REGION_ENTRY_INVALID)
 			goto out;
 		table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
 		/* fallthrough */
 	case _ASCE_TYPE_REGION3:
 		table += (address & _REGION3_INDEX) >> _REGION3_SHIFT;
 		if (bad_address(table))
 			goto bad;
 		pr_cont("R3:%016lx ", *table);
 		if (*table & (_REGION_ENTRY_INVALID | _REGION3_ENTRY_LARGE))
 			goto out;
 		table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
 		/* fallthrough */
 	case _ASCE_TYPE_SEGMENT:
 		table += (address & _SEGMENT_INDEX) >> _SEGMENT_SHIFT;
 		if (bad_address(table))
 			goto bad;
 		pr_cont("S:%016lx ", *table);
 		if (*table & (_SEGMENT_ENTRY_INVALID | _SEGMENT_ENTRY_LARGE))
 			goto out;
 		table = (unsigned long *)(*table & _SEGMENT_ENTRY_ORIGIN);
 	}
 	table += (address & _PAGE_INDEX) >> _PAGE_SHIFT;
 	if (bad_address(table))
 		goto bad;
 	pr_cont("P:%016lx ", *table);
 out:
 	pr_cont("\n");
 	return;
 bad:
 	pr_cont("BAD\n");
 }

 static void dump_fault_info(struct pt_regs *regs)
 {
 	unsigned long asce;

 	pr_alert("Failing address: %016lx TEID: %016lx\n",
 		 regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
 	pr_alert("Fault in ");
 	switch (regs->int_parm_long & 3) {
 	case 3:
 		pr_cont("home space ");
 		break;
 	case 2:
 		pr_cont("secondary space ");
 		break;
 	case 1:
 		pr_cont("access register ");
 		break;
 	case 0:
 		pr_cont("primary space ");
 		break;
 	}
 	pr_cont("mode while using ");
 	switch (get_fault_type(regs)) {
 	case USER_FAULT:
 		asce = S390_lowcore.user_asce;
 		pr_cont("user ");
 		break;
 	case VDSO_FAULT:
 		asce = S390_lowcore.vdso_asce;
 		pr_cont("vdso ");
 		break;
 	case GMAP_FAULT:
 		asce = ((struct gmap *) S390_lowcore.gmap)->asce;
 		pr_cont("gmap ");
 		break;
 	case KERNEL_FAULT:
 		asce = S390_lowcore.kernel_asce;
 		pr_cont("kernel ");
 		break;
 	}
 	pr_cont("ASCE.\n");
 	dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
 }

 int show_unhandled_signals = 1;

 void report_user_fault(struct pt_regs *regs, long signr, int is_mm_fault)
 {
 	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 %04x ilc:%d ",
 	       regs->int_code & 0xffff, regs->int_code >> 17);
 	print_vma_addr(KERN_CONT "in ", regs->psw.addr);
 	printk(KERN_CONT "\n");
 	if (is_mm_fault)
 		dump_fault_info(regs);
 	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)
 {
 	report_user_fault(regs, SIGSEGV, 1);
 	force_sig_fault(SIGSEGV, si_code,
 			(void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK),
 			current);
 }

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

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

 	/*
 	 * Oops. The kernel tried to access some bad page. We'll have to
 	 * terminate things with extreme prejudice.
 	 */
 	if (get_fault_type(regs) == KERNEL_FAULT)
 		printk(KERN_ALERT "Unable to handle kernel pointer dereference"
 		       " in virtual kernel address space\n");
 	else
 		printk(KERN_ALERT "Unable to handle kernel paging request"
 		       " in virtual user address space\n");
 	dump_fault_info(regs);
 	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)
 {
 	/*
 	 * Send a sigbus, regardless of whether we were in kernel
 	 * or user mode.
 	 */
 	force_sig_fault(SIGBUS, BUS_ADRERR,
 			(void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK),
 			current);
 }

 static noinline int signal_return(struct pt_regs *regs)
 {
 	u16 instruction;
 	int rc;

 	rc = __get_user(instruction, (u16 __user *) regs->psw.addr);
 	if (rc)
 		return rc;
 	if (instruction == 0x0a77) {
 		set_pt_regs_flag(regs, PIF_SYSCALL);
 		regs->int_code = 0x00040077;
 		return 0;
 	} else if (instruction == 0x0aad) {
 		set_pt_regs_flag(regs, PIF_SYSCALL);
 		regs->int_code = 0x000400ad;
 		return 0;
 	}
 	return -EACCES;
 }

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

 	switch (fault) {
 	case VM_FAULT_BADACCESS:
 		if (access == VM_EXEC && signal_return(regs) == 0)
 			break;
 	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);
 			break;
 		}
 	case VM_FAULT_BADCONTEXT:
 	case VM_FAULT_PFAULT:
 		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_SIGSEGV) {
 			/* Kernel mode? Handle exceptions or die */
 			if (!user_mode(regs))
 				do_no_context(regs);
 			else
 				do_sigsegv(regs, SEGV_MAPERR);
 		} 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 gmap *gmap;
 	struct task_struct *tsk;
 	struct mm_struct *mm;
 	struct vm_area_struct *vma;
 	enum fault_type type;
 	unsigned long trans_exc_code;
 	unsigned long address;
 	unsigned int flags;
 	int fault;

 	tsk = current;
 	/*
 	 * The instruction that caused the program check has
 	 * been nullified. Don't signal single step via SIGTRAP.
 	 */
 	clear_pt_regs_flag(regs, PIF_PER_TRAP);

 	if (notify_page_fault(regs))
 		return 0;

 	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;
 	type = get_fault_type(regs);
 	switch (type) {
 	case KERNEL_FAULT:
 		goto out;
 	case VDSO_FAULT:
 		fault = VM_FAULT_BADMAP;
 		goto out;
 	case USER_FAULT:
 	case GMAP_FAULT:
 		if (faulthandler_disabled() || !mm)
 			goto out;
 		break;
 	}

 	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 (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
 	if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
 		flags |= FAULT_FLAG_WRITE;
 	down_read(&mm->mmap_sem);

 	gmap = NULL;
 	if (IS_ENABLED(CONFIG_PGSTE) && type == GMAP_FAULT) {
 		gmap = (struct gmap *) S390_lowcore.gmap;
 		current->thread.gmap_addr = address;
 		current->thread.gmap_write_flag = !!(flags & FAULT_FLAG_WRITE);
 		current->thread.gmap_int_code = regs->int_code & 0xffff;
 		address = __gmap_translate(gmap, address);
 		if (address == -EFAULT) {
 			fault = VM_FAULT_BADMAP;
 			goto out_up;
 		}
 		if (gmap->pfault_enabled)
 			flags |= FAULT_FLAG_RETRY_NOWAIT;
 	}

 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(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) {
 			if (IS_ENABLED(CONFIG_PGSTE) && gmap &&
 			    (flags & FAULT_FLAG_RETRY_NOWAIT)) {
 				/* FAULT_FLAG_RETRY_NOWAIT has been set,
 				 * mmap_sem has not been released */
 				current->thread.gmap_pfault = 1;
 				fault = VM_FAULT_PFAULT;
 				goto out_up;
 			}
 			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
 			 * of starvation. */
 			flags &= ~(FAULT_FLAG_ALLOW_RETRY |
 				   FAULT_FLAG_RETRY_NOWAIT);
 			flags |= FAULT_FLAG_TRIED;
 			down_read(&mm->mmap_sem);
 			goto retry;
 		}
 	}
 	if (IS_ENABLED(CONFIG_PGSTE) && gmap) {
 		address =  __gmap_link(gmap, current->thread.gmap_addr,
 				       address);
 		if (address == -EFAULT) {
 			fault = VM_FAULT_BADMAP;
 			goto out_up;
 		}
 		if (address == -ENOMEM) {
 			fault = VM_FAULT_OOM;
 			goto out_up;
 		}
 	}
 	fault = 0;
 out_up:
 	up_read(&mm->mmap_sem);
 out:
 	return fault;
 }

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

 	trans_exc_code = regs->int_parm_long;
 	/*
 	 * Protection exceptions are suppressing, decrement psw address.
 	 * The exception to this rule are aborted transactions, for these
 	 * the PSW already points to the correct location.
 	 */
 	if (!(regs->int_code & 0x200))
 		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;
 	}
 	if (unlikely(MACHINE_HAS_NX && (trans_exc_code & 0x80))) {
 		regs->int_parm_long = (trans_exc_code & ~PAGE_MASK) |
 					(regs->psw.addr & PAGE_MASK);
 		access = VM_EXEC;
 		fault = VM_FAULT_BADACCESS;
 	} else {
 		access = VM_WRITE;
 		fault = do_exception(regs, access);
 	}
 	if (unlikely(fault))
 		do_fault_error(regs, access, fault);
 }
 NOKPROBE_SYMBOL(do_protection_exception);

 void 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, access, fault);
 }
 NOKPROBE_SYMBOL(do_dat_exception);

 #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_LPP,
 		.refselmk = 1ULL << 48,
 		.refcmpmk = 1ULL << 48,
 		.reserved = __PF_RES_FIELD };
         int rc;

 	if (pfault_disable)
 		return -1;
 	diag_stat_inc(DIAG_STAT_X258);
 	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;
 	diag_stat_inc(DIAG_STAT_X258);
 	asm volatile(
 		"	diag	%0,0,0x258\n"
 		"0:	nopr	%%r7\n"
 		EX_TABLE(0b,0b)
 		: : "a" (&refbk), "m" (refbk) : "cc");
 }

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

 #define PF_COMPLETE	0x0080

 /*
  * The mechanism of our pfault code: if Linux is running as guest, runs a user
  * space process and the user space process accesses a page that the host has
  * paged out we get a pfault interrupt.
  *
  * This allows us, within the guest, to schedule a different process. Without
  * this mechanism the host would have to suspend the whole virtual cpu until
  * the page has been paged in.
  *
  * So when we get such an interrupt then we set the state of the current task
  * to uninterruptible and also set the need_resched flag. Both happens within
  * interrupt context(!). If we later on want to return to user space we
  * recognize the need_resched flag and then call schedule().  It's not very
  * obvious how this works...
  *
  * Of course we have a lot of additional fun with the completion interrupt (->
  * host signals that a page of a process has been paged in and the process can
  * continue to run). This interrupt can arrive on any cpu and, since we have
  * virtual cpus, actually appear before the interrupt that signals that a page
  * is missing.
  */
 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;
 	inc_irq_stat(IRQEXT_PFL);
 	/* Get the token (= pid of the affected task). */
 	pid = param64 & LPP_PID_MASK;
 	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 & PF_COMPLETE) {
 		/* 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 */
 			goto block;
 		} 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);
 block:
 			/* Since this must be a userspace fault, there
 			 * is no kernel task state to trample. Rely on the
 			 * return to userspace schedule() to block. */
 			__set_current_state(TASK_UNINTERRUPTIBLE);
 			set_tsk_need_resched(tsk);
 			set_preempt_need_resched();
 		}
 	}
 out:
 	spin_unlock(&pfault_lock);
 	put_task_struct(tsk);
 }

 static int pfault_cpu_dead(unsigned int cpu)
 {
 	struct thread_struct *thread, *next;
 	struct task_struct *tsk;

 	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);
 	return 0;
 }

 static int __init pfault_irq_init(void)
 {
 	int rc;

 	rc = register_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
 	if (rc)
 		goto out_extint;
 	rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
 	if (rc)
 		goto out_pfault;
 	irq_subclass_register(IRQ_SUBCLASS_SERVICE_SIGNAL);
 	cpuhp_setup_state_nocalls(CPUHP_S390_PFAULT_DEAD, "s390/pfault:dead",
 				  NULL, pfault_cpu_dead);
 	return 0;

 out_pfault:
 	unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
 out_extint:
 	pfault_disable = 1;
 	return rc;
 }
 early_initcall(pfault_irq_init);

 #endif /* CONFIG_PFAULT */
	// SPDX-License-Identifier: GPL-2.0
	/*
	* S390 version
	* Copyright IBM Corp. 1999
	* 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/sched/debug.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/extable.h>
	#include <linux/hardirq.h>
	#include <linux/kprobes.h>
	#include <linux/uaccess.h>
	#include <linux/hugetlb.h>
	#include <asm/asm-offsets.h>
	#include <asm/diag.h>
	#include <asm/pgtable.h>
	#include <asm/gmap.h>
	#include <asm/irq.h>
	#include <asm/mmu_context.h>
	#include <asm/facility.h>
	#include "../kernel/entry.h"

	#define __FAIL_ADDR_MASK -4096L
	#define __SUBCODE_MASK 0x0600
	#define __PF_RES_FIELD 0x8000000000000000ULL

	#define VM_FAULT_BADCONTEXT 0x010000
	#define VM_FAULT_BADMAP 0x020000
	#define VM_FAULT_BADACCESS 0x040000
	#define VM_FAULT_SIGNAL 0x080000
	#define VM_FAULT_PFAULT 0x100000

	enum fault_type {
	KERNEL_FAULT,
	USER_FAULT,
	VDSO_FAULT,
	GMAP_FAULT,
	};

	static unsigned long store_indication __read_mostly;

	static int __init fault_init(void)
	{
	if (test_facility(75))
	store_indication = 0xc00;
	return 0;
	}
	early_initcall(fault_init);

	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;
	}
	}

	/*
	* Find out which address space caused the exception.
	* Access register mode is impossible, ignore space == 3.
	*/
	static inline enum fault_type get_fault_type(struct pt_regs *regs)
	{
	unsigned long trans_exc_code;

	trans_exc_code = regs->int_parm_long & 3;
	if (likely(trans_exc_code == 0)) {
	/* primary space exception */
	if (IS_ENABLED(CONFIG_PGSTE) &&
	test_pt_regs_flag(regs, PIF_GUEST_FAULT))
	return GMAP_FAULT;
	if (current->thread.mm_segment == USER_DS)
	return USER_FAULT;
	return KERNEL_FAULT;
	}
	if (trans_exc_code == 2) {
	/* secondary space exception */
	if (current->thread.mm_segment & 1) {
	if (current->thread.mm_segment == USER_DS_SACF)
	return USER_FAULT;
	return KERNEL_FAULT;
	}
	return VDSO_FAULT;
	}
	/* home space exception -> access via kernel ASCE */
	return KERNEL_FAULT;
	}

	static int bad_address(void *p)
	{
	unsigned long dummy;

	return probe_kernel_address((unsigned long *)p, dummy);
	}

	static void dump_pagetable(unsigned long asce, unsigned long address)
	{
	unsigned long *table = __va(asce & _ASCE_ORIGIN);

	pr_alert("AS:%016lx ", asce);
	switch (asce & _ASCE_TYPE_MASK) {
	case _ASCE_TYPE_REGION1:
	table += (address & _REGION1_INDEX) >> _REGION1_SHIFT;
	if (bad_address(table))
	goto bad;
	pr_cont("R1:%016lx ", *table);
	if (*table & _REGION_ENTRY_INVALID)
	goto out;
	table = (unsigned long )(table & _REGION_ENTRY_ORIGIN);
	/* fallthrough */
	case _ASCE_TYPE_REGION2:
	table += (address & _REGION2_INDEX) >> _REGION2_SHIFT;
	if (bad_address(table))
	goto bad;
	pr_cont("R2:%016lx ", *table);
	if (*table & _REGION_ENTRY_INVALID)
	goto out;
	table = (unsigned long )(table & _REGION_ENTRY_ORIGIN);
	/* fallthrough */
	case _ASCE_TYPE_REGION3:
	table += (address & _REGION3_INDEX) >> _REGION3_SHIFT;
	if (bad_address(table))
	goto bad;
	pr_cont("R3:%016lx ", *table);
	if (*table & (_REGION_ENTRY_INVALID \| _REGION3_ENTRY_LARGE))
	goto out;
	table = (unsigned long )(table & _REGION_ENTRY_ORIGIN);
	/* fallthrough */
	case _ASCE_TYPE_SEGMENT:
	table += (address & _SEGMENT_INDEX) >> _SEGMENT_SHIFT;
	if (bad_address(table))
	goto bad;
	pr_cont("S:%016lx ", *table);
	if (*table & (_SEGMENT_ENTRY_INVALID \| _SEGMENT_ENTRY_LARGE))
	goto out;
	table = (unsigned long )(table & _SEGMENT_ENTRY_ORIGIN);
	}
	table += (address & _PAGE_INDEX) >> _PAGE_SHIFT;
	if (bad_address(table))
	goto bad;
	pr_cont("P:%016lx ", *table);
	out:
	pr_cont("\n");
	return;
	bad:
	pr_cont("BAD\n");
	}

	static void dump_fault_info(struct pt_regs *regs)
	{
	unsigned long asce;

	pr_alert("Failing address: %016lx TEID: %016lx\n",
	regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
	pr_alert("Fault in ");
	switch (regs->int_parm_long & 3) {
	case 3:
	pr_cont("home space ");
	break;
	case 2:
	pr_cont("secondary space ");
	break;
	case 1:
	pr_cont("access register ");
	break;
	case 0:
	pr_cont("primary space ");
	break;
	}
	pr_cont("mode while using ");
	switch (get_fault_type(regs)) {
	case USER_FAULT:
	asce = S390_lowcore.user_asce;
	pr_cont("user ");
	break;
	case VDSO_FAULT:
	asce = S390_lowcore.vdso_asce;
	pr_cont("vdso ");
	break;
	case GMAP_FAULT:
	asce = ((struct gmap *) S390_lowcore.gmap)->asce;
	pr_cont("gmap ");
	break;
	case KERNEL_FAULT:
	asce = S390_lowcore.kernel_asce;
	pr_cont("kernel ");
	break;
	}
	pr_cont("ASCE.\n");
	dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
	}

	int show_unhandled_signals = 1;

	void report_user_fault(struct pt_regs *regs, long signr, int is_mm_fault)
	{
	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 %04x ilc:%d ",
	regs->int_code & 0xffff, regs->int_code >> 17);
	print_vma_addr(KERN_CONT "in ", regs->psw.addr);
	printk(KERN_CONT "\n");
	if (is_mm_fault)
	dump_fault_info(regs);
	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)
	{
	report_user_fault(regs, SIGSEGV, 1);
	force_sig_fault(SIGSEGV, si_code,
	(void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK),
	current);
	}

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

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

	/*
	* Oops. The kernel tried to access some bad page. We'll have to
	* terminate things with extreme prejudice.
	*/
	if (get_fault_type(regs) == KERNEL_FAULT)
	printk(KERN_ALERT "Unable to handle kernel pointer dereference"
	" in virtual kernel address space\n");
	else
	printk(KERN_ALERT "Unable to handle kernel paging request"
	" in virtual user address space\n");
	dump_fault_info(regs);
	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)
	{
	/*
	* Send a sigbus, regardless of whether we were in kernel
	* or user mode.
	*/
	force_sig_fault(SIGBUS, BUS_ADRERR,
	(void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK),
	current);
	}

	static noinline int signal_return(struct pt_regs *regs)
	{
	u16 instruction;
	int rc;

	rc = __get_user(instruction, (u16 __user *) regs->psw.addr);
	if (rc)
	return rc;
	if (instruction == 0x0a77) {
	set_pt_regs_flag(regs, PIF_SYSCALL);
	regs->int_code = 0x00040077;
	return 0;
	} else if (instruction == 0x0aad) {
	set_pt_regs_flag(regs, PIF_SYSCALL);
	regs->int_code = 0x000400ad;
	return 0;
	}
	return -EACCES;
	}

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

	switch (fault) {
	case VM_FAULT_BADACCESS:
	if (access == VM_EXEC && signal_return(regs) == 0)
	break;
	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);
	break;
	}
	case VM_FAULT_BADCONTEXT:
	case VM_FAULT_PFAULT:
	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_SIGSEGV) {
	/* Kernel mode? Handle exceptions or die */
	if (!user_mode(regs))
	do_no_context(regs);
	else
	do_sigsegv(regs, SEGV_MAPERR);
	} 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 gmap *gmap;
	struct task_struct *tsk;
	struct mm_struct *mm;
	struct vm_area_struct *vma;
	enum fault_type type;
	unsigned long trans_exc_code;
	unsigned long address;
	unsigned int flags;
	int fault;

	tsk = current;
	/*
	* The instruction that caused the program check has
	* been nullified. Don't signal single step via SIGTRAP.
	*/
	clear_pt_regs_flag(regs, PIF_PER_TRAP);

	if (notify_page_fault(regs))
	return 0;

	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;
	type = get_fault_type(regs);
	switch (type) {
	case KERNEL_FAULT:
	goto out;
	case VDSO_FAULT:
	fault = VM_FAULT_BADMAP;
	goto out;
	case USER_FAULT:
	case GMAP_FAULT:
	if (faulthandler_disabled() \|\| !mm)
	goto out;
	break;
	}

	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 (user_mode(regs))
	flags \|= FAULT_FLAG_USER;
	if (access == VM_WRITE \|\| (trans_exc_code & store_indication) == 0x400)
	flags \|= FAULT_FLAG_WRITE;
	down_read(&mm->mmap_sem);

	gmap = NULL;
	if (IS_ENABLED(CONFIG_PGSTE) && type == GMAP_FAULT) {
	gmap = (struct gmap *) S390_lowcore.gmap;
	current->thread.gmap_addr = address;
	current->thread.gmap_write_flag = !!(flags & FAULT_FLAG_WRITE);
	current->thread.gmap_int_code = regs->int_code & 0xffff;
	address = __gmap_translate(gmap, address);
	if (address == -EFAULT) {
	fault = VM_FAULT_BADMAP;
	goto out_up;
	}
	if (gmap->pfault_enabled)
	flags \|= FAULT_FLAG_RETRY_NOWAIT;
	}

	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(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) {
	if (IS_ENABLED(CONFIG_PGSTE) && gmap &&
	(flags & FAULT_FLAG_RETRY_NOWAIT)) {
	/* FAULT_FLAG_RETRY_NOWAIT has been set,
	* mmap_sem has not been released */
	current->thread.gmap_pfault = 1;
	fault = VM_FAULT_PFAULT;
	goto out_up;
	}
	/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
	* of starvation. */
	flags &= ~(FAULT_FLAG_ALLOW_RETRY \|
	FAULT_FLAG_RETRY_NOWAIT);
	flags \|= FAULT_FLAG_TRIED;
	down_read(&mm->mmap_sem);
	goto retry;
	}
	}
	if (IS_ENABLED(CONFIG_PGSTE) && gmap) {
	address = __gmap_link(gmap, current->thread.gmap_addr,
	address);
	if (address == -EFAULT) {
	fault = VM_FAULT_BADMAP;
	goto out_up;
	}
	if (address == -ENOMEM) {
	fault = VM_FAULT_OOM;
	goto out_up;
	}
	}
	fault = 0;
	out_up:
	up_read(&mm->mmap_sem);
	out:
	return fault;
	}

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

	trans_exc_code = regs->int_parm_long;
	/*
	* Protection exceptions are suppressing, decrement psw address.
	* The exception to this rule are aborted transactions, for these
	* the PSW already points to the correct location.
	*/
	if (!(regs->int_code & 0x200))
	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;
	}
	if (unlikely(MACHINE_HAS_NX && (trans_exc_code & 0x80))) {
	regs->int_parm_long = (trans_exc_code & ~PAGE_MASK) \|
	(regs->psw.addr & PAGE_MASK);
	access = VM_EXEC;
	fault = VM_FAULT_BADACCESS;
	} else {
	access = VM_WRITE;
	fault = do_exception(regs, access);
	}
	if (unlikely(fault))
	do_fault_error(regs, access, fault);
	}
	NOKPROBE_SYMBOL(do_protection_exception);

	void 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, access, fault);
	}
	NOKPROBE_SYMBOL(do_dat_exception);

	#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_LPP,
	.refselmk = 1ULL << 48,
	.refcmpmk = 1ULL << 48,
	.reserved = __PF_RES_FIELD };
	int rc;

	if (pfault_disable)
	return -1;
	diag_stat_inc(DIAG_STAT_X258);
	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;
	diag_stat_inc(DIAG_STAT_X258);
	asm volatile(
	" diag %0,0,0x258\n"
	"0: nopr %%r7\n"
	EX_TABLE(0b,0b)
	: : "a" (&refbk), "m" (refbk) : "cc");
	}

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

	#define PF_COMPLETE 0x0080

	/*
	* The mechanism of our pfault code: if Linux is running as guest, runs a user
	* space process and the user space process accesses a page that the host has
	* paged out we get a pfault interrupt.
	*
	* This allows us, within the guest, to schedule a different process. Without
	* this mechanism the host would have to suspend the whole virtual cpu until
	* the page has been paged in.
	*
	* So when we get such an interrupt then we set the state of the current task
	* to uninterruptible and also set the need_resched flag. Both happens within
	* interrupt context(!). If we later on want to return to user space we
	* recognize the need_resched flag and then call schedule(). It's not very
	* obvious how this works...
	*
	* Of course we have a lot of additional fun with the completion interrupt (->
	* host signals that a page of a process has been paged in and the process can
	* continue to run). This interrupt can arrive on any cpu and, since we have
	* virtual cpus, actually appear before the interrupt that signals that a page
	* is missing.
	*/
	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;
	inc_irq_stat(IRQEXT_PFL);
	/* Get the token (= pid of the affected task). */
	pid = param64 & LPP_PID_MASK;
	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 & PF_COMPLETE) {
	/* 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 */
	goto block;
	} 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);
	block:
	/* Since this must be a userspace fault, there
	* is no kernel task state to trample. Rely on the
	* return to userspace schedule() to block. */
	__set_current_state(TASK_UNINTERRUPTIBLE);
	set_tsk_need_resched(tsk);
	set_preempt_need_resched();
	}
	}
	out:
	spin_unlock(&pfault_lock);
	put_task_struct(tsk);
	}

	static int pfault_cpu_dead(unsigned int cpu)
	{
	struct thread_struct thread, next;
	struct task_struct *tsk;

	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);
	return 0;
	}

	static int __init pfault_irq_init(void)
	{
	int rc;

	rc = register_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
	if (rc)
	goto out_extint;
	rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
	if (rc)
	goto out_pfault;
	irq_subclass_register(IRQ_SUBCLASS_SERVICE_SIGNAL);
	cpuhp_setup_state_nocalls(CPUHP_S390_PFAULT_DEAD, "s390/pfault:dead",
	NULL, pfault_cpu_dead);
	return 0;

	out_pfault:
	unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
	out_extint:
	pfault_disable = 1;
	return rc;
	}
	early_initcall(pfault_irq_init);

	#endif /* CONFIG_PFAULT */