arch/powerpc/mm/fault.c - linux - Git at Google

 /*
  *  PowerPC version
  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
  *
  *  Derived from "arch/i386/mm/fault.c"
  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  *
  *  Modified by Cort Dougan and Paul Mackerras.
  *
  *  Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
  *
  *  This program is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU General Public License
  *  as published by the Free Software Foundation; either version
  *  2 of the License, or (at your option) any later version.
  */

 #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/interrupt.h>
 #include <linux/highmem.h>
 #include <linux/module.h>
 #include <linux/kprobes.h>
 #include <linux/kdebug.h>
 #include <linux/perf_event.h>
 #include <linux/magic.h>
 #include <linux/ratelimit.h>

 #include <asm/firmware.h>
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/mmu.h>
 #include <asm/mmu_context.h>
 #include <asm/uaccess.h>
 #include <asm/tlbflush.h>
 #include <asm/siginfo.h>
 #include <asm/debug.h>
 #include <mm/mmu_decl.h>

 #include "icswx.h"

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

 	/* kprobe_running() needs smp_processor_id() */
 	if (!user_mode(regs)) {
 		preempt_disable();
 		if (kprobe_running() && kprobe_fault_handler(regs, 11))
 			ret = 1;
 		preempt_enable();
 	}

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

 /*
  * Check whether the instruction at regs->nip is a store using
  * an update addressing form which will update r1.
  */
 static int store_updates_sp(struct pt_regs *regs)
 {
 	unsigned int inst;

 	if (get_user(inst, (unsigned int __user *)regs->nip))
 		return 0;
 	/* check for 1 in the rA field */
 	if (((inst >> 16) & 0x1f) != 1)
 		return 0;
 	/* check major opcode */
 	switch (inst >> 26) {
 	case 37:	/* stwu */
 	case 39:	/* stbu */
 	case 45:	/* sthu */
 	case 53:	/* stfsu */
 	case 55:	/* stfdu */
 		return 1;
 	case 62:	/* std or stdu */
 		return (inst & 3) == 1;
 	case 31:
 		/* check minor opcode */
 		switch ((inst >> 1) & 0x3ff) {
 		case 181:	/* stdux */
 		case 183:	/* stwux */
 		case 247:	/* stbux */
 		case 439:	/* sthux */
 		case 695:	/* stfsux */
 		case 759:	/* stfdux */
 			return 1;
 		}
 	}
 	return 0;
 }
 /*
  * do_page_fault error handling helpers
  */

 #define MM_FAULT_RETURN		0
 #define MM_FAULT_CONTINUE	-1
 #define MM_FAULT_ERR(sig)	(sig)

 static int out_of_memory(struct pt_regs *regs)
 {
 	/*
 	 * We ran out of memory, or some other thing happened to us that made
 	 * us unable to handle the page fault gracefully.
 	 */
 	up_read(&current->mm->mmap_sem);
 	if (!user_mode(regs))
 		return MM_FAULT_ERR(SIGKILL);
 	pagefault_out_of_memory();
 	return MM_FAULT_RETURN;
 }

 static int do_sigbus(struct pt_regs *regs, unsigned long address)
 {
 	siginfo_t info;

 	up_read(&current->mm->mmap_sem);

 	if (user_mode(regs)) {
 		current->thread.trap_nr = BUS_ADRERR;
 		info.si_signo = SIGBUS;
 		info.si_errno = 0;
 		info.si_code = BUS_ADRERR;
 		info.si_addr = (void __user *)address;
 		force_sig_info(SIGBUS, &info, current);
 		return MM_FAULT_RETURN;
 	}
 	return MM_FAULT_ERR(SIGBUS);
 }

 static int mm_fault_error(struct pt_regs *regs, unsigned long addr, int fault)
 {
 	/*
 	 * Pagefault was interrupted by SIGKILL. We have no reason to
 	 * continue the pagefault.
 	 */
 	if (fatal_signal_pending(current)) {
 		/*
 		 * If we have retry set, the mmap semaphore will have
 		 * alrady been released in __lock_page_or_retry(). Else
 		 * we release it now.
 		 */
 		if (!(fault & VM_FAULT_RETRY))
 			up_read(&current->mm->mmap_sem);
 		/* Coming from kernel, we need to deal with uaccess fixups */
 		if (user_mode(regs))
 			return MM_FAULT_RETURN;
 		return MM_FAULT_ERR(SIGKILL);
 	}

 	/* No fault: be happy */
 	if (!(fault & VM_FAULT_ERROR))
 		return MM_FAULT_CONTINUE;

 	/* Out of memory */
 	if (fault & VM_FAULT_OOM)
 		return out_of_memory(regs);

 	/* Bus error. x86 handles HWPOISON here, we'll add this if/when
 	 * we support the feature in HW
 	 */
 	if (fault & VM_FAULT_SIGBUS)
 		return do_sigbus(regs, addr);

 	/* We don't understand the fault code, this is fatal */
 	BUG();
 	return MM_FAULT_CONTINUE;
 }

 /*
  * For 600- and 800-family processors, the error_code parameter is DSISR
  * for a data fault, SRR1 for an instruction fault. For 400-family processors
  * the error_code parameter is ESR for a data fault, 0 for an instruction
  * fault.
  * For 64-bit processors, the error_code parameter is
  *  - DSISR for a non-SLB data access fault,
  *  - SRR1 & 0x08000000 for a non-SLB instruction access fault
  *  - 0 any SLB fault.
  *
  * The return value is 0 if the fault was handled, or the signal
  * number if this is a kernel fault that can't be handled here.
  */
 int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
 			    unsigned long error_code)
 {
 	struct vm_area_struct * vma;
 	struct mm_struct *mm = current->mm;
 	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 	int code = SEGV_MAPERR;
 	int is_write = 0;
 	int trap = TRAP(regs);
  	int is_exec = trap == 0x400;
 	int fault;

 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
 	/*
 	 * Fortunately the bit assignments in SRR1 for an instruction
 	 * fault and DSISR for a data fault are mostly the same for the
 	 * bits we are interested in.  But there are some bits which
 	 * indicate errors in DSISR but can validly be set in SRR1.
 	 */
 	if (trap == 0x400)
 		error_code &= 0x48200000;
 	else
 		is_write = error_code & DSISR_ISSTORE;
 #else
 	is_write = error_code & ESR_DST;
 #endif /* CONFIG_4xx || CONFIG_BOOKE */

 	if (is_write)
 		flags |= FAULT_FLAG_WRITE;

 #ifdef CONFIG_PPC_ICSWX
 	/*
 	 * we need to do this early because this "data storage
 	 * interrupt" does not update the DAR/DEAR so we don't want to
 	 * look at it
 	 */
 	if (error_code & ICSWX_DSI_UCT) {
 		int rc = acop_handle_fault(regs, address, error_code);
 		if (rc)
 			return rc;
 	}
 #endif /* CONFIG_PPC_ICSWX */

 	if (notify_page_fault(regs))
 		return 0;

 	if (unlikely(debugger_fault_handler(regs)))
 		return 0;

 	/* On a kernel SLB miss we can only check for a valid exception entry */
 	if (!user_mode(regs) && (address >= TASK_SIZE))
 		return SIGSEGV;

 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE) || \
 			     defined(CONFIG_PPC_BOOK3S_64))
   	if (error_code & DSISR_DABRMATCH) {
 		/* DABR match */
 		do_dabr(regs, address, error_code);
 		return 0;
 	}
 #endif

 	/* We restore the interrupt state now */
 	if (!arch_irq_disabled_regs(regs))
 		local_irq_enable();

 	if (in_atomic() || mm == NULL) {
 		if (!user_mode(regs))
 			return SIGSEGV;
 		/* in_atomic() in user mode is really bad,
 		   as is current->mm == NULL. */
 		printk(KERN_EMERG "Page fault in user mode with "
 		       "in_atomic() = %d mm = %p\n", in_atomic(), mm);
 		printk(KERN_EMERG "NIP = %lx  MSR = %lx\n",
 		       regs->nip, regs->msr);
 		die("Weird page fault", regs, SIGSEGV);
 	}

 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

 	/* When running in the kernel we expect faults to occur only to
 	 * addresses in user space.  All other faults represent errors in the
 	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
 	 * erroneous fault occurring in a code path which already holds mmap_sem
 	 * we will deadlock attempting to validate the fault against the
 	 * address space.  Luckily the kernel only validly references user
 	 * space from well defined areas of code, which are listed in the
 	 * exceptions table.
 	 *
 	 * As the vast majority of faults will be valid we will only perform
 	 * the source reference check when there is a possibility of a deadlock.
 	 * Attempt to lock the address space, if we cannot we then validate the
 	 * source.  If this is invalid we can skip the address space check,
 	 * thus avoiding the deadlock.
 	 */
 	if (!down_read_trylock(&mm->mmap_sem)) {
 		if (!user_mode(regs) && !search_exception_tables(regs->nip))
 			goto bad_area_nosemaphore;

 retry:
 		down_read(&mm->mmap_sem);
 	} else {
 		/*
 		 * The above down_read_trylock() might have succeeded in
 		 * which case we'll have missed the might_sleep() from
 		 * down_read():
 		 */
 		might_sleep();
 	}

 	vma = find_vma(mm, address);
 	if (!vma)
 		goto bad_area;
 	if (vma->vm_start <= address)
 		goto good_area;
 	if (!(vma->vm_flags & VM_GROWSDOWN))
 		goto bad_area;

 	/*
 	 * N.B. The POWER/Open ABI allows programs to access up to
 	 * 288 bytes below the stack pointer.
 	 * The kernel signal delivery code writes up to about 1.5kB
 	 * below the stack pointer (r1) before decrementing it.
 	 * The exec code can write slightly over 640kB to the stack
 	 * before setting the user r1.  Thus we allow the stack to
 	 * expand to 1MB without further checks.
 	 */
 	if (address + 0x100000 < vma->vm_end) {
 		/* get user regs even if this fault is in kernel mode */
 		struct pt_regs *uregs = current->thread.regs;
 		if (uregs == NULL)
 			goto bad_area;

 		/*
 		 * A user-mode access to an address a long way below
 		 * the stack pointer is only valid if the instruction
 		 * is one which would update the stack pointer to the
 		 * address accessed if the instruction completed,
 		 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
 		 * (or the byte, halfword, float or double forms).
 		 *
 		 * If we don't check this then any write to the area
 		 * between the last mapped region and the stack will
 		 * expand the stack rather than segfaulting.
 		 */
 		if (address + 2048 < uregs->gpr[1]
 		    && (!user_mode(regs) || !store_updates_sp(regs)))
 			goto bad_area;
 	}
 	if (expand_stack(vma, address))
 		goto bad_area;

 good_area:
 	code = SEGV_ACCERR;
 #if defined(CONFIG_6xx)
 	if (error_code & 0x95700000)
 		/* an error such as lwarx to I/O controller space,
 		   address matching DABR, eciwx, etc. */
 		goto bad_area;
 #endif /* CONFIG_6xx */
 #if defined(CONFIG_8xx)
 	/* 8xx sometimes need to load a invalid/non-present TLBs.
 	 * These must be invalidated separately as linux mm don't.
 	 */
 	if (error_code & 0x40000000) /* no translation? */
 		_tlbil_va(address, 0, 0, 0);

         /* The MPC8xx seems to always set 0x80000000, which is
          * "undefined".  Of those that can be set, this is the only
          * one which seems bad.
          */
 	if (error_code & 0x10000000)
                 /* Guarded storage error. */
 		goto bad_area;
 #endif /* CONFIG_8xx */

 	if (is_exec) {
 #ifdef CONFIG_PPC_STD_MMU
 		/* Protection fault on exec go straight to failure on
 		 * Hash based MMUs as they either don't support per-page
 		 * execute permission, or if they do, it's handled already
 		 * at the hash level. This test would probably have to
 		 * be removed if we change the way this works to make hash
 		 * processors use the same I/D cache coherency mechanism
 		 * as embedded.
 		 */
 		if (error_code & DSISR_PROTFAULT)
 			goto bad_area;
 #endif /* CONFIG_PPC_STD_MMU */

 		/*
 		 * Allow execution from readable areas if the MMU does not
 		 * provide separate controls over reading and executing.
 		 *
 		 * Note: That code used to not be enabled for 4xx/BookE.
 		 * It is now as I/D cache coherency for these is done at
 		 * set_pte_at() time and I see no reason why the test
 		 * below wouldn't be valid on those processors. This -may-
 		 * break programs compiled with a really old ABI though.
 		 */
 		if (!(vma->vm_flags & VM_EXEC) &&
 		    (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
 		     !(vma->vm_flags & (VM_READ | VM_WRITE))))
 			goto bad_area;
 	/* a write */
 	} else if (is_write) {
 		if (!(vma->vm_flags & VM_WRITE))
 			goto bad_area;
 	/* a read */
 	} else {
 		/* protection fault */
 		if (error_code & 0x08000000)
 			goto bad_area;
 		if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
 			goto bad_area;
 	}

 	/*
 	 * If for any reason at all we couldn't handle the fault,
 	 * make sure we exit gracefully rather than endlessly redo
 	 * the fault.
 	 */
 	fault = handle_mm_fault(mm, vma, address, flags);
 	if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) {
 		int rc = mm_fault_error(regs, address, fault);
 		if (rc >= MM_FAULT_RETURN)
 			return rc;
 	}

 	/*
 	 * 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) {
 			current->maj_flt++;
 			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
 				      regs, address);
 #ifdef CONFIG_PPC_SMLPAR
 			if (firmware_has_feature(FW_FEATURE_CMO)) {
 				preempt_disable();
 				get_lppaca()->page_ins += (1 << PAGE_FACTOR);
 				preempt_enable();
 			}
 #endif /* CONFIG_PPC_SMLPAR */
 		} else {
 			current->min_flt++;
 			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
 				      regs, address);
 		}
 		if (fault & VM_FAULT_RETRY) {
 			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
 			 * of starvation. */
 			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			goto retry;
 		}
 	}

 	up_read(&mm->mmap_sem);
 	return 0;

 bad_area:
 	up_read(&mm->mmap_sem);

 bad_area_nosemaphore:
 	/* User mode accesses cause a SIGSEGV */
 	if (user_mode(regs)) {
 		_exception(SIGSEGV, regs, code, address);
 		return 0;
 	}

 	if (is_exec && (error_code & DSISR_PROTFAULT))
 		printk_ratelimited(KERN_CRIT "kernel tried to execute NX-protected"
 				   " page (%lx) - exploit attempt? (uid: %d)\n",
 				   address, from_kuid(&init_user_ns, current_uid()));

 	return SIGSEGV;

 }

 /*
  * bad_page_fault is called when we have a bad access from the kernel.
  * It is called from the DSI and ISI handlers in head.S and from some
  * of the procedures in traps.c.
  */
 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 {
 	const struct exception_table_entry *entry;
 	unsigned long *stackend;

 	/* Are we prepared to handle this fault?  */
 	if ((entry = search_exception_tables(regs->nip)) != NULL) {
 		regs->nip = entry->fixup;
 		return;
 	}

 	/* kernel has accessed a bad area */

 	switch (regs->trap) {
 	case 0x300:
 	case 0x380:
 		printk(KERN_ALERT "Unable to handle kernel paging request for "
 			"data at address 0x%08lx\n", regs->dar);
 		break;
 	case 0x400:
 	case 0x480:
 		printk(KERN_ALERT "Unable to handle kernel paging request for "
 			"instruction fetch\n");
 		break;
 	default:
 		printk(KERN_ALERT "Unable to handle kernel paging request for "
 			"unknown fault\n");
 		break;
 	}
 	printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
 		regs->nip);

 	stackend = end_of_stack(current);
 	if (current != &init_task && *stackend != STACK_END_MAGIC)
 		printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");

 	die("Kernel access of bad area", regs, sig);
 }
	/*
	* PowerPC version
	* Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
	*
	* Derived from "arch/i386/mm/fault.c"
	* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
	*
	* Modified by Cort Dougan and Paul Mackerras.
	*
	* Modified for PPC64 by Dave Engebretsen (engebret@ibm.com)
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* as published by the Free Software Foundation; either version
	* 2 of the License, or (at your option) any later version.
	*/

	#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/interrupt.h>
	#include <linux/highmem.h>
	#include <linux/module.h>
	#include <linux/kprobes.h>
	#include <linux/kdebug.h>
	#include <linux/perf_event.h>
	#include <linux/magic.h>
	#include <linux/ratelimit.h>

	#include <asm/firmware.h>
	#include <asm/page.h>
	#include <asm/pgtable.h>
	#include <asm/mmu.h>
	#include <asm/mmu_context.h>
	#include <asm/uaccess.h>
	#include <asm/tlbflush.h>
	#include <asm/siginfo.h>
	#include <asm/debug.h>
	#include <mm/mmu_decl.h>

	#include "icswx.h"

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

	/* kprobe_running() needs smp_processor_id() */
	if (!user_mode(regs)) {
	preempt_disable();
	if (kprobe_running() && kprobe_fault_handler(regs, 11))
	ret = 1;
	preempt_enable();
	}

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

	/*
	* Check whether the instruction at regs->nip is a store using
	* an update addressing form which will update r1.
	*/
	static int store_updates_sp(struct pt_regs *regs)
	{
	unsigned int inst;

	if (get_user(inst, (unsigned int __user *)regs->nip))
	return 0;
	/* check for 1 in the rA field */
	if (((inst >> 16) & 0x1f) != 1)
	return 0;
	/* check major opcode */
	switch (inst >> 26) {
	case 37: /* stwu */
	case 39: /* stbu */
	case 45: /* sthu */
	case 53: /* stfsu */
	case 55: /* stfdu */
	return 1;
	case 62: /* std or stdu */
	return (inst & 3) == 1;
	case 31:
	/* check minor opcode */
	switch ((inst >> 1) & 0x3ff) {
	case 181: /* stdux */
	case 183: /* stwux */
	case 247: /* stbux */
	case 439: /* sthux */
	case 695: /* stfsux */
	case 759: /* stfdux */
	return 1;
	}
	}
	return 0;
	}
	/*
	* do_page_fault error handling helpers
	*/

	#define MM_FAULT_RETURN 0
	#define MM_FAULT_CONTINUE -1
	#define MM_FAULT_ERR(sig) (sig)

	static int out_of_memory(struct pt_regs *regs)
	{
	/*
	* We ran out of memory, or some other thing happened to us that made
	* us unable to handle the page fault gracefully.
	*/
	up_read(&current->mm->mmap_sem);
	if (!user_mode(regs))
	return MM_FAULT_ERR(SIGKILL);
	pagefault_out_of_memory();
	return MM_FAULT_RETURN;
	}

	static int do_sigbus(struct pt_regs *regs, unsigned long address)
	{
	siginfo_t info;

	up_read(&current->mm->mmap_sem);

	if (user_mode(regs)) {
	current->thread.trap_nr = BUS_ADRERR;
	info.si_signo = SIGBUS;
	info.si_errno = 0;
	info.si_code = BUS_ADRERR;
	info.si_addr = (void __user *)address;
	force_sig_info(SIGBUS, &info, current);
	return MM_FAULT_RETURN;
	}
	return MM_FAULT_ERR(SIGBUS);
	}

	static int mm_fault_error(struct pt_regs *regs, unsigned long addr, int fault)
	{
	/*
	* Pagefault was interrupted by SIGKILL. We have no reason to
	* continue the pagefault.
	*/
	if (fatal_signal_pending(current)) {
	/*
	* If we have retry set, the mmap semaphore will have
	* alrady been released in __lock_page_or_retry(). Else
	* we release it now.
	*/
	if (!(fault & VM_FAULT_RETRY))
	up_read(&current->mm->mmap_sem);
	/* Coming from kernel, we need to deal with uaccess fixups */
	if (user_mode(regs))
	return MM_FAULT_RETURN;
	return MM_FAULT_ERR(SIGKILL);
	}

	/* No fault: be happy */
	if (!(fault & VM_FAULT_ERROR))
	return MM_FAULT_CONTINUE;

	/* Out of memory */
	if (fault & VM_FAULT_OOM)
	return out_of_memory(regs);

	/* Bus error. x86 handles HWPOISON here, we'll add this if/when
	* we support the feature in HW
	*/
	if (fault & VM_FAULT_SIGBUS)
	return do_sigbus(regs, addr);

	/* We don't understand the fault code, this is fatal */
	BUG();
	return MM_FAULT_CONTINUE;
	}

	/*
	* For 600- and 800-family processors, the error_code parameter is DSISR
	* for a data fault, SRR1 for an instruction fault. For 400-family processors
	* the error_code parameter is ESR for a data fault, 0 for an instruction
	* fault.
	* For 64-bit processors, the error_code parameter is
	* - DSISR for a non-SLB data access fault,
	* - SRR1 & 0x08000000 for a non-SLB instruction access fault
	* - 0 any SLB fault.
	*
	* The return value is 0 if the fault was handled, or the signal
	* number if this is a kernel fault that can't be handled here.
	*/
	int __kprobes do_page_fault(struct pt_regs *regs, unsigned long address,
	unsigned long error_code)
	{
	struct vm_area_struct * vma;
	struct mm_struct *mm = current->mm;
	unsigned int flags = FAULT_FLAG_ALLOW_RETRY \| FAULT_FLAG_KILLABLE;
	int code = SEGV_MAPERR;
	int is_write = 0;
	int trap = TRAP(regs);
	int is_exec = trap == 0x400;
	int fault;

	#if !(defined(CONFIG_4xx) \|\| defined(CONFIG_BOOKE))
	/*
	* Fortunately the bit assignments in SRR1 for an instruction
	* fault and DSISR for a data fault are mostly the same for the
	* bits we are interested in. But there are some bits which
	* indicate errors in DSISR but can validly be set in SRR1.
	*/
	if (trap == 0x400)
	error_code &= 0x48200000;
	else
	is_write = error_code & DSISR_ISSTORE;
	#else
	is_write = error_code & ESR_DST;
	#endif /* CONFIG_4xx \|\| CONFIG_BOOKE */

	if (is_write)
	flags \|= FAULT_FLAG_WRITE;

	#ifdef CONFIG_PPC_ICSWX
	/*
	* we need to do this early because this "data storage
	* interrupt" does not update the DAR/DEAR so we don't want to
	* look at it
	*/
	if (error_code & ICSWX_DSI_UCT) {
	int rc = acop_handle_fault(regs, address, error_code);
	if (rc)
	return rc;
	}
	#endif /* CONFIG_PPC_ICSWX */

	if (notify_page_fault(regs))
	return 0;

	if (unlikely(debugger_fault_handler(regs)))
	return 0;

	/* On a kernel SLB miss we can only check for a valid exception entry */
	if (!user_mode(regs) && (address >= TASK_SIZE))
	return SIGSEGV;

	#if !(defined(CONFIG_4xx) \|\| defined(CONFIG_BOOKE) \|\| \
	defined(CONFIG_PPC_BOOK3S_64))
	if (error_code & DSISR_DABRMATCH) {
	/* DABR match */
	do_dabr(regs, address, error_code);
	return 0;
	}
	#endif

	/* We restore the interrupt state now */
	if (!arch_irq_disabled_regs(regs))
	local_irq_enable();

	if (in_atomic() \|\| mm == NULL) {
	if (!user_mode(regs))
	return SIGSEGV;
	/* in_atomic() in user mode is really bad,
	as is current->mm == NULL. */
	printk(KERN_EMERG "Page fault in user mode with "
	"in_atomic() = %d mm = %p\n", in_atomic(), mm);
	printk(KERN_EMERG "NIP = %lx MSR = %lx\n",
	regs->nip, regs->msr);
	die("Weird page fault", regs, SIGSEGV);
	}

	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

	/* When running in the kernel we expect faults to occur only to
	* addresses in user space. All other faults represent errors in the
	* kernel and should generate an OOPS. Unfortunately, in the case of an
	* erroneous fault occurring in a code path which already holds mmap_sem
	* we will deadlock attempting to validate the fault against the
	* address space. Luckily the kernel only validly references user
	* space from well defined areas of code, which are listed in the
	* exceptions table.
	*
	* As the vast majority of faults will be valid we will only perform
	* the source reference check when there is a possibility of a deadlock.
	* Attempt to lock the address space, if we cannot we then validate the
	* source. If this is invalid we can skip the address space check,
	* thus avoiding the deadlock.
	*/
	if (!down_read_trylock(&mm->mmap_sem)) {
	if (!user_mode(regs) && !search_exception_tables(regs->nip))
	goto bad_area_nosemaphore;

	retry:
	down_read(&mm->mmap_sem);
	} else {
	/*
	* The above down_read_trylock() might have succeeded in
	* which case we'll have missed the might_sleep() from
	* down_read():
	*/
	might_sleep();
	}

	vma = find_vma(mm, address);
	if (!vma)
	goto bad_area;
	if (vma->vm_start <= address)
	goto good_area;
	if (!(vma->vm_flags & VM_GROWSDOWN))
	goto bad_area;

	/*
	* N.B. The POWER/Open ABI allows programs to access up to
	* 288 bytes below the stack pointer.
	* The kernel signal delivery code writes up to about 1.5kB
	* below the stack pointer (r1) before decrementing it.
	* The exec code can write slightly over 640kB to the stack
	* before setting the user r1. Thus we allow the stack to
	* expand to 1MB without further checks.
	*/
	if (address + 0x100000 < vma->vm_end) {
	/* get user regs even if this fault is in kernel mode */
	struct pt_regs *uregs = current->thread.regs;
	if (uregs == NULL)
	goto bad_area;

	/*
	* A user-mode access to an address a long way below
	* the stack pointer is only valid if the instruction
	* is one which would update the stack pointer to the
	* address accessed if the instruction completed,
	* i.e. either stwu rs,n(r1) or stwux rs,r1,rb
	* (or the byte, halfword, float or double forms).
	*
	* If we don't check this then any write to the area
	* between the last mapped region and the stack will
	* expand the stack rather than segfaulting.
	*/
	if (address + 2048 < uregs->gpr[1]
	&& (!user_mode(regs) \|\| !store_updates_sp(regs)))
	goto bad_area;
	}
	if (expand_stack(vma, address))
	goto bad_area;

	good_area:
	code = SEGV_ACCERR;
	#if defined(CONFIG_6xx)
	if (error_code & 0x95700000)
	/* an error such as lwarx to I/O controller space,
	address matching DABR, eciwx, etc. */
	goto bad_area;
	#endif /* CONFIG_6xx */
	#if defined(CONFIG_8xx)
	/* 8xx sometimes need to load a invalid/non-present TLBs.
	* These must be invalidated separately as linux mm don't.
	*/
	if (error_code & 0x40000000) /* no translation? */
	_tlbil_va(address, 0, 0, 0);

	/* The MPC8xx seems to always set 0x80000000, which is
	* "undefined". Of those that can be set, this is the only
	* one which seems bad.
	*/
	if (error_code & 0x10000000)
	/* Guarded storage error. */
	goto bad_area;
	#endif /* CONFIG_8xx */

	if (is_exec) {
	#ifdef CONFIG_PPC_STD_MMU
	/* Protection fault on exec go straight to failure on
	* Hash based MMUs as they either don't support per-page
	* execute permission, or if they do, it's handled already
	* at the hash level. This test would probably have to
	* be removed if we change the way this works to make hash
	* processors use the same I/D cache coherency mechanism
	* as embedded.
	*/
	if (error_code & DSISR_PROTFAULT)
	goto bad_area;
	#endif /* CONFIG_PPC_STD_MMU */

	/*
	* Allow execution from readable areas if the MMU does not
	* provide separate controls over reading and executing.
	*
	* Note: That code used to not be enabled for 4xx/BookE.
	* It is now as I/D cache coherency for these is done at
	* set_pte_at() time and I see no reason why the test
	* below wouldn't be valid on those processors. This -may-
	* break programs compiled with a really old ABI though.
	*/
	if (!(vma->vm_flags & VM_EXEC) &&
	(cpu_has_feature(CPU_FTR_NOEXECUTE) \|\|
	!(vma->vm_flags & (VM_READ \| VM_WRITE))))
	goto bad_area;
	/* a write */
	} else if (is_write) {
	if (!(vma->vm_flags & VM_WRITE))
	goto bad_area;
	/* a read */
	} else {
	/* protection fault */
	if (error_code & 0x08000000)
	goto bad_area;
	if (!(vma->vm_flags & (VM_READ \| VM_EXEC \| VM_WRITE)))
	goto bad_area;
	}

	/*
	* If for any reason at all we couldn't handle the fault,
	* make sure we exit gracefully rather than endlessly redo
	* the fault.
	*/
	fault = handle_mm_fault(mm, vma, address, flags);
	if (unlikely(fault & (VM_FAULT_RETRY\|VM_FAULT_ERROR))) {
	int rc = mm_fault_error(regs, address, fault);
	if (rc >= MM_FAULT_RETURN)
	return rc;
	}

	/*
	* 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) {
	current->maj_flt++;
	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
	regs, address);
	#ifdef CONFIG_PPC_SMLPAR
	if (firmware_has_feature(FW_FEATURE_CMO)) {
	preempt_disable();
	get_lppaca()->page_ins += (1 << PAGE_FACTOR);
	preempt_enable();
	}
	#endif /* CONFIG_PPC_SMLPAR */
	} else {
	current->min_flt++;
	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
	regs, address);
	}
	if (fault & VM_FAULT_RETRY) {
	/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
	* of starvation. */
	flags &= ~FAULT_FLAG_ALLOW_RETRY;
	goto retry;
	}
	}

	up_read(&mm->mmap_sem);
	return 0;

	bad_area:
	up_read(&mm->mmap_sem);

	bad_area_nosemaphore:
	/* User mode accesses cause a SIGSEGV */
	if (user_mode(regs)) {
	_exception(SIGSEGV, regs, code, address);
	return 0;
	}

	if (is_exec && (error_code & DSISR_PROTFAULT))
	printk_ratelimited(KERN_CRIT "kernel tried to execute NX-protected"
	" page (%lx) - exploit attempt? (uid: %d)\n",
	address, from_kuid(&init_user_ns, current_uid()));

	return SIGSEGV;

	}

	/*
	* bad_page_fault is called when we have a bad access from the kernel.
	* It is called from the DSI and ISI handlers in head.S and from some
	* of the procedures in traps.c.
	*/
	void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
	{
	const struct exception_table_entry *entry;
	unsigned long *stackend;

	/* Are we prepared to handle this fault? */
	if ((entry = search_exception_tables(regs->nip)) != NULL) {
	regs->nip = entry->fixup;
	return;
	}

	/* kernel has accessed a bad area */

	switch (regs->trap) {
	case 0x300:
	case 0x380:
	printk(KERN_ALERT "Unable to handle kernel paging request for "
	"data at address 0x%08lx\n", regs->dar);
	break;
	case 0x400:
	case 0x480:
	printk(KERN_ALERT "Unable to handle kernel paging request for "
	"instruction fetch\n");
	break;
	default:
	printk(KERN_ALERT "Unable to handle kernel paging request for "
	"unknown fault\n");
	break;
	}
	printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
	regs->nip);

	stackend = end_of_stack(current);
	if (current != &init_task && *stackend != STACK_END_MAGIC)
	printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");

	die("Kernel access of bad area", regs, sig);
	}