arch/x86_64/mm/fault.c - fp2-dev/kernel/msm - Gitiles

 /*
  *  linux/arch/x86-64/mm/fault.c
  *
  *  Copyright (C) 1995  Linus Torvalds
  *  Copyright (C) 2001,2002 Andi Kleen, SuSE Labs.
  */

 #include <linux/config.h>
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/ptrace.h>
 #include <linux/mman.h>
 #include <linux/mm.h>
 #include <linux/smp.h>
 #include <linux/smp_lock.h>
 #include <linux/interrupt.h>
 #include <linux/init.h>
 #include <linux/tty.h>
 #include <linux/vt_kern.h>		/* For unblank_screen() */
 #include <linux/compiler.h>
 #include <linux/module.h>
 #include <linux/kprobes.h>

 #include <asm/system.h>
 #include <asm/uaccess.h>
 #include <asm/pgalloc.h>
 #include <asm/smp.h>
 #include <asm/tlbflush.h>
 #include <asm/proto.h>
 #include <asm/kdebug.h>
 #include <asm-generic/sections.h>
 #include <asm/kdebug.h>

 void bust_spinlocks(int yes)
 {
 	int loglevel_save = console_loglevel;
 	if (yes) {
 		oops_in_progress = 1;
 	} else {
 #ifdef CONFIG_VT
 		unblank_screen();
 #endif
 		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;		/* NMI oopser may have shut the console up */
 		printk(" ");
 		console_loglevel = loglevel_save;
 	}
 }

 /* Sometimes the CPU reports invalid exceptions on prefetch.
    Check that here and ignore.
    Opcode checker based on code by Richard Brunner */
 static noinline int is_prefetch(struct pt_regs *regs, unsigned long addr,
 				unsigned long error_code)
 {
 	unsigned char *instr = (unsigned char *)(regs->rip);
 	int scan_more = 1;
 	int prefetch = 0;
 	unsigned char *max_instr = instr + 15;

 	/* If it was a exec fault ignore */
 	if (error_code & (1<<4))
 		return 0;

 	/* Code segments in LDT could have a non zero base. Don't check
 	   when that's possible */
 	if (regs->cs & (1<<2))
 		return 0;

 	if ((regs->cs & 3) != 0 && regs->rip >= TASK_SIZE)
 		return 0;

 	while (scan_more && instr < max_instr) {
 		unsigned char opcode;
 		unsigned char instr_hi;
 		unsigned char instr_lo;

 		if (__get_user(opcode, instr))
 			break;

 		instr_hi = opcode & 0xf0;
 		instr_lo = opcode & 0x0f;
 		instr++;

 		switch (instr_hi) {
 		case 0x20:
 		case 0x30:
 			/* Values 0x26,0x2E,0x36,0x3E are valid x86
 			   prefixes.  In long mode, the CPU will signal
 			   invalid opcode if some of these prefixes are
 			   present so we will never get here anyway */
 			scan_more = ((instr_lo & 7) == 0x6);
 			break;

 		case 0x40:
 			/* In AMD64 long mode, 0x40 to 0x4F are valid REX prefixes
 			   Need to figure out under what instruction mode the
 			   instruction was issued ... */
 			/* Could check the LDT for lm, but for now it's good
 			   enough to assume that long mode only uses well known
 			   segments or kernel. */
 			scan_more = ((regs->cs & 3) == 0) || (regs->cs == __USER_CS);
 			break;

 		case 0x60:
 			/* 0x64 thru 0x67 are valid prefixes in all modes. */
 			scan_more = (instr_lo & 0xC) == 0x4;
 			break;
 		case 0xF0:
 			/* 0xF0, 0xF2, and 0xF3 are valid prefixes in all modes. */
 			scan_more = !instr_lo || (instr_lo>>1) == 1;
 			break;
 		case 0x00:
 			/* Prefetch instruction is 0x0F0D or 0x0F18 */
 			scan_more = 0;
 			if (__get_user(opcode, instr))
 				break;
 			prefetch = (instr_lo == 0xF) &&
 				(opcode == 0x0D || opcode == 0x18);
 			break;
 		default:
 			scan_more = 0;
 			break;
 		}
 	}
 	return prefetch;
 }

 static int bad_address(void *p)
 {
 	unsigned long dummy;
 	return __get_user(dummy, (unsigned long *)p);
 }

 void dump_pagetable(unsigned long address)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
 	pte_t *pte;

 	asm("movq %%cr3,%0" : "=r" (pgd));

 	pgd = __va((unsigned long)pgd & PHYSICAL_PAGE_MASK);
 	pgd += pgd_index(address);
 	printk("PGD %lx ", pgd_val(*pgd));
 	if (bad_address(pgd)) goto bad;
 	if (!pgd_present(*pgd)) goto ret;

 	pud = __pud_offset_k((pud_t *)pgd_page(*pgd), address);
 	if (bad_address(pud)) goto bad;
 	printk("PUD %lx ", pud_val(*pud));
 	if (!pud_present(*pud))	goto ret;

 	pmd = pmd_offset(pud, address);
 	if (bad_address(pmd)) goto bad;
 	printk("PMD %lx ", pmd_val(*pmd));
 	if (!pmd_present(*pmd))	goto ret;

 	pte = pte_offset_kernel(pmd, address);
 	if (bad_address(pte)) goto bad;
 	printk("PTE %lx", pte_val(*pte));
 ret:
 	printk("\n");
 	return;
 bad:
 	printk("BAD\n");
 }

 static const char errata93_warning[] =
 KERN_ERR "******* Your BIOS seems to not contain a fix for K8 errata #93\n"
 KERN_ERR "******* Working around it, but it may cause SEGVs or burn power.\n"
 KERN_ERR "******* Please consider a BIOS update.\n"
 KERN_ERR "******* Disabling USB legacy in the BIOS may also help.\n";

 /* Workaround for K8 erratum #93 & buggy BIOS.
    BIOS SMM functions are required to use a specific workaround
    to avoid corruption of the 64bit RIP register on C stepping K8.
    A lot of BIOS that didn't get tested properly miss this.
    The OS sees this as a page fault with the upper 32bits of RIP cleared.
    Try to work around it here.
    Note we only handle faults in kernel here. */

 static int is_errata93(struct pt_regs *regs, unsigned long address)
 {
 	static int warned;
 	if (address != regs->rip)
 		return 0;
 	if ((address >> 32) != 0)
 		return 0;
 	address |= 0xffffffffUL << 32;
 	if ((address >= (u64)_stext && address <= (u64)_etext) ||
 	    (address >= MODULES_VADDR && address <= MODULES_END)) {
 		if (!warned) {
 			printk(errata93_warning);
 			warned = 1;
 		}
 		regs->rip = address;
 		return 1;
 	}
 	return 0;
 }

 int unhandled_signal(struct task_struct *tsk, int sig)
 {
 	if (tsk->pid == 1)
 		return 1;
 	/* Warn for strace, but not for gdb */
 	if (!test_ti_thread_flag(tsk->thread_info, TIF_SYSCALL_TRACE) &&
 	    (tsk->ptrace & PT_PTRACED))
 		return 0;
 	return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_IGN) ||
 		(tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
 }

 static noinline void pgtable_bad(unsigned long address, struct pt_regs *regs,
 				 unsigned long error_code)
 {
 	oops_begin();
 	printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
 	       current->comm, address);
 	dump_pagetable(address);
 	__die("Bad pagetable", regs, error_code);
 	oops_end();
 	do_exit(SIGKILL);
 }

 /*
  * Handle a fault on the vmalloc or module mapping area
  */
 static int vmalloc_fault(unsigned long address)
 {
 	pgd_t *pgd, *pgd_ref;
 	pud_t *pud, *pud_ref;
 	pmd_t *pmd, *pmd_ref;
 	pte_t *pte, *pte_ref;

 	/* Copy kernel mappings over when needed. This can also
 	   happen within a race in page table update. In the later
 	   case just flush. */

 	pgd = pgd_offset(current->mm ?: &init_mm, address);
 	pgd_ref = pgd_offset_k(address);
 	if (pgd_none(*pgd_ref))
 		return -1;
 	if (pgd_none(*pgd))
 		set_pgd(pgd, *pgd_ref);

 	/* Below here mismatches are bugs because these lower tables
 	   are shared */

 	pud = pud_offset(pgd, address);
 	pud_ref = pud_offset(pgd_ref, address);
 	if (pud_none(*pud_ref))
 		return -1;
 	if (pud_none(*pud) || pud_page(*pud) != pud_page(*pud_ref))
 		BUG();
 	pmd = pmd_offset(pud, address);
 	pmd_ref = pmd_offset(pud_ref, address);
 	if (pmd_none(*pmd_ref))
 		return -1;
 	if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
 		BUG();
 	pte_ref = pte_offset_kernel(pmd_ref, address);
 	if (!pte_present(*pte_ref))
 		return -1;
 	pte = pte_offset_kernel(pmd, address);
 	if (!pte_present(*pte) || pte_page(*pte) != pte_page(*pte_ref))
 		BUG();
 	__flush_tlb_all();
 	return 0;
 }

 int page_fault_trace = 0;
 int exception_trace = 1;

 /*
  * 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:
  *	bit 0 == 0 means no page found, 1 means protection fault
  *	bit 1 == 0 means read, 1 means write
  *	bit 2 == 0 means kernel, 1 means user-mode
  *      bit 3 == 1 means fault was an instruction fetch
  */
 asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code)
 {
 	struct task_struct *tsk;
 	struct mm_struct *mm;
 	struct vm_area_struct * vma;
 	unsigned long address;
 	const struct exception_table_entry *fixup;
 	int write;
 	siginfo_t info;

 #ifdef CONFIG_CHECKING
 	{
 		unsigned long gs;
 		struct x8664_pda *pda = cpu_pda + stack_smp_processor_id();
 		rdmsrl(MSR_GS_BASE, gs);
 		if (gs != (unsigned long)pda) {
 			wrmsrl(MSR_GS_BASE, pda);
 			printk("page_fault: wrong gs %lx expected %p\n", gs, pda);
 		}
 	}
 #endif

 	/* get the address */
 	__asm__("movq %%cr2,%0":"=r" (address));
 	if (notify_die(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
 					SIGSEGV) == NOTIFY_STOP)
 		return;

 	if (likely(regs->eflags & X86_EFLAGS_IF))
 		local_irq_enable();

 	if (unlikely(page_fault_trace))
 		printk("pagefault rip:%lx rsp:%lx cs:%lu ss:%lu address %lx error %lx\n",
 		       regs->rip,regs->rsp,regs->cs,regs->ss,address,error_code);

 	tsk = current;
 	mm = tsk->mm;
 	info.si_code = SEGV_MAPERR;


 	/*
 	 * We fault-in kernel-space virtual memory on-demand. The
 	 * 'reference' page table is init_mm.pgd.
 	 *
 	 * NOTE! We MUST NOT take any locks for this case. We may
 	 * be in an interrupt or a critical region, and should
 	 * only copy the information from the master page table,
 	 * nothing more.
 	 *
 	 * This verifies that the fault happens in kernel space
 	 * (error_code & 4) == 0, and that the fault was not a
 	 * protection error (error_code & 1) == 0.
 	 */
 	if (unlikely(address >= TASK_SIZE)) {
 		if (!(error_code & 5)) {
 			if (vmalloc_fault(address) < 0)
 				goto bad_area_nosemaphore;
 			return;
 		}
 		/*
 		 * Don't take the mm semaphore here. If we fixup a prefetch
 		 * fault we could otherwise deadlock.
 		 */
 		goto bad_area_nosemaphore;
 	}

 	if (unlikely(error_code & (1 << 3)))
 		pgtable_bad(address, regs, error_code);

 	/*
 	 * If we're in an interrupt or have no user
 	 * context, we must not take the fault..
 	 */
 	if (unlikely(in_atomic() || !mm))
 		goto bad_area_nosemaphore;

  again:
 	/* 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.  Unfortunatly, in the case of an
 	 * erroneous fault occuring 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 possibilty 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 ((error_code & 4) == 0 &&
 		    !search_exception_tables(regs->rip))
 			goto bad_area_nosemaphore;
 		down_read(&mm->mmap_sem);
 	}

 	vma = find_vma(mm, address);
 	if (!vma)
 		goto bad_area;
 	if (likely(vma->vm_start <= address))
 		goto good_area;
 	if (!(vma->vm_flags & VM_GROWSDOWN))
 		goto bad_area;
 	if (error_code & 4) {
 		// XXX: align red zone size with ABI
 		if (address + 128 < regs->rsp)
 			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:
 	info.si_code = SEGV_ACCERR;
 	write = 0;
 	switch (error_code & 3) {
 		default:	/* 3: write, present */
 			/* fall through */
 		case 2:		/* write, not present */
 			if (!(vma->vm_flags & VM_WRITE))
 				goto bad_area;
 			write++;
 			break;
 		case 1:		/* read, present */
 			goto bad_area;
 		case 0:		/* read, not present */
 			if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
 				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.
 	 */
 	switch (handle_mm_fault(mm, vma, address, write)) {
 	case 1:
 		tsk->min_flt++;
 		break;
 	case 2:
 		tsk->maj_flt++;
 		break;
 	case 0:
 		goto do_sigbus;
 	default:
 		goto out_of_memory;
 	}

 	up_read(&mm->mmap_sem);
 	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);

 bad_area_nosemaphore:

 #ifdef CONFIG_IA32_EMULATION
 	/* 32bit vsyscall. map on demand. */
 	if (test_thread_flag(TIF_IA32) &&
 	    address >= VSYSCALL32_BASE && address < VSYSCALL32_END) {
 		if (map_syscall32(mm, address) < 0)
 			goto out_of_memory2;
 		return;
 	}
 #endif

 	/* User mode accesses just cause a SIGSEGV */
 	if (error_code & 4) {
 		if (is_prefetch(regs, address, error_code))
 			return;

 		/* Work around K8 erratum #100 K8 in compat mode
 		   occasionally jumps to illegal addresses >4GB.  We
 		   catch this here in the page fault handler because
 		   these addresses are not reachable. Just detect this
 		   case and return.  Any code segment in LDT is
 		   compatibility mode. */
 		if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) &&
 		    (address >> 32))
 			return;

 		if (exception_trace && unhandled_signal(tsk, SIGSEGV)) {
 			printk(
 		       "%s%s[%d]: segfault at %016lx rip %016lx rsp %016lx error %lx\n",
 					tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
 					tsk->comm, tsk->pid, address, regs->rip,
 					regs->rsp, error_code);
 		}

 		tsk->thread.cr2 = address;
 		/* Kernel addresses are always protection faults */
 		tsk->thread.error_code = error_code | (address >= TASK_SIZE);
 		tsk->thread.trap_no = 14;
 		info.si_signo = SIGSEGV;
 		info.si_errno = 0;
 		/* info.si_code has been set above */
 		info.si_addr = (void __user *)address;
 		force_sig_info(SIGSEGV, &info, tsk);
 		return;
 	}

 no_context:

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

 	/*
 	 * Hall of shame of CPU/BIOS bugs.
 	 */

  	if (is_prefetch(regs, address, error_code))
  		return;

 	if (is_errata93(regs, address))
 		return;

 /*
  * Oops. The kernel tried to access some bad page. We'll have to
  * terminate things with extreme prejudice.
  */

 	oops_begin();

 	if (address < PAGE_SIZE)
 		printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
 	else
 		printk(KERN_ALERT "Unable to handle kernel paging request");
 	printk(" at %016lx RIP: \n" KERN_ALERT,address);
 	printk_address(regs->rip);
 	printk("\n");
 	dump_pagetable(address);
 	__die("Oops", regs, error_code);
 	/* Executive summary in case the body of the oops scrolled away */
 	printk(KERN_EMERG "CR2: %016lx\n", address);
 	oops_end();
 	do_exit(SIGKILL);

 /*
  * We ran out of memory, or some other thing happened to us that made
  * us unable to handle the page fault gracefully.
  */
 out_of_memory:
 	up_read(&mm->mmap_sem);
 out_of_memory2:
 	if (current->pid == 1) {
 		yield();
 		goto again;
 	}
 	printk("VM: killing process %s\n", tsk->comm);
 	if (error_code & 4)
 		do_exit(SIGKILL);
 	goto no_context;

 do_sigbus:
 	up_read(&mm->mmap_sem);

 	/* Kernel mode? Handle exceptions or die */
 	if (!(error_code & 4))
 		goto no_context;

 	tsk->thread.cr2 = address;
 	tsk->thread.error_code = error_code;
 	tsk->thread.trap_no = 14;
 	info.si_signo = SIGBUS;
 	info.si_errno = 0;
 	info.si_code = BUS_ADRERR;
 	info.si_addr = (void __user *)address;
 	force_sig_info(SIGBUS, &info, tsk);
 	return;
 }
	/*
	* linux/arch/x86-64/mm/fault.c
	*
	* Copyright (C) 1995 Linus Torvalds
	* Copyright (C) 2001,2002 Andi Kleen, SuSE Labs.
	*/

	#include <linux/config.h>
	#include <linux/signal.h>
	#include <linux/sched.h>
	#include <linux/kernel.h>
	#include <linux/errno.h>
	#include <linux/string.h>
	#include <linux/types.h>
	#include <linux/ptrace.h>
	#include <linux/mman.h>
	#include <linux/mm.h>
	#include <linux/smp.h>
	#include <linux/smp_lock.h>
	#include <linux/interrupt.h>
	#include <linux/init.h>
	#include <linux/tty.h>
	#include <linux/vt_kern.h> /* For unblank_screen() */
	#include <linux/compiler.h>
	#include <linux/module.h>
	#include <linux/kprobes.h>

	#include <asm/system.h>
	#include <asm/uaccess.h>
	#include <asm/pgalloc.h>
	#include <asm/smp.h>
	#include <asm/tlbflush.h>
	#include <asm/proto.h>
	#include <asm/kdebug.h>
	#include <asm-generic/sections.h>
	#include <asm/kdebug.h>

	void bust_spinlocks(int yes)
	{
	int loglevel_save = console_loglevel;
	if (yes) {
	oops_in_progress = 1;
	} else {
	#ifdef CONFIG_VT
	unblank_screen();
	#endif
	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; /* NMI oopser may have shut the console up */
	printk(" ");
	console_loglevel = loglevel_save;
	}
	}

	/* Sometimes the CPU reports invalid exceptions on prefetch.
	Check that here and ignore.
	Opcode checker based on code by Richard Brunner */
	static noinline int is_prefetch(struct pt_regs *regs, unsigned long addr,
	unsigned long error_code)
	{
	unsigned char instr = (unsigned char )(regs->rip);
	int scan_more = 1;
	int prefetch = 0;
	unsigned char *max_instr = instr + 15;

	/* If it was a exec fault ignore */
	if (error_code & (1<<4))
	return 0;

	/* Code segments in LDT could have a non zero base. Don't check
	when that's possible */
	if (regs->cs & (1<<2))
	return 0;

	if ((regs->cs & 3) != 0 && regs->rip >= TASK_SIZE)
	return 0;

	while (scan_more && instr < max_instr) {
	unsigned char opcode;
	unsigned char instr_hi;
	unsigned char instr_lo;

	if (__get_user(opcode, instr))
	break;

	instr_hi = opcode & 0xf0;
	instr_lo = opcode & 0x0f;
	instr++;

	switch (instr_hi) {
	case 0x20:
	case 0x30:
	/* Values 0x26,0x2E,0x36,0x3E are valid x86
	prefixes. In long mode, the CPU will signal
	invalid opcode if some of these prefixes are
	present so we will never get here anyway */
	scan_more = ((instr_lo & 7) == 0x6);
	break;

	case 0x40:
	/* In AMD64 long mode, 0x40 to 0x4F are valid REX prefixes
	Need to figure out under what instruction mode the
	instruction was issued ... */
	/* Could check the LDT for lm, but for now it's good
	enough to assume that long mode only uses well known
	segments or kernel. */
	scan_more = ((regs->cs & 3) == 0) \|\| (regs->cs == __USER_CS);
	break;

	case 0x60:
	/* 0x64 thru 0x67 are valid prefixes in all modes. */
	scan_more = (instr_lo & 0xC) == 0x4;
	break;
	case 0xF0:
	/* 0xF0, 0xF2, and 0xF3 are valid prefixes in all modes. */
	scan_more = !instr_lo \|\| (instr_lo>>1) == 1;
	break;
	case 0x00:
	/* Prefetch instruction is 0x0F0D or 0x0F18 */
	scan_more = 0;
	if (__get_user(opcode, instr))
	break;
	prefetch = (instr_lo == 0xF) &&
	(opcode == 0x0D \|\| opcode == 0x18);
	break;
	default:
	scan_more = 0;
	break;
	}
	}
	return prefetch;
	}

	static int bad_address(void *p)
	{
	unsigned long dummy;
	return __get_user(dummy, (unsigned long *)p);
	}

	void dump_pagetable(unsigned long address)
	{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;

	asm("movq %%cr3,%0" : "=r" (pgd));

	pgd = __va((unsigned long)pgd & PHYSICAL_PAGE_MASK);
	pgd += pgd_index(address);
	printk("PGD %lx ", pgd_val(*pgd));
	if (bad_address(pgd)) goto bad;
	if (!pgd_present(*pgd)) goto ret;

	pud = __pud_offset_k((pud_t )pgd_page(pgd), address);
	if (bad_address(pud)) goto bad;
	printk("PUD %lx ", pud_val(*pud));
	if (!pud_present(*pud)) goto ret;

	pmd = pmd_offset(pud, address);
	if (bad_address(pmd)) goto bad;
	printk("PMD %lx ", pmd_val(*pmd));
	if (!pmd_present(*pmd)) goto ret;

	pte = pte_offset_kernel(pmd, address);
	if (bad_address(pte)) goto bad;
	printk("PTE %lx", pte_val(*pte));
	ret:
	printk("\n");
	return;
	bad:
	printk("BAD\n");
	}

	static const char errata93_warning[] =
	KERN_ERR "******* Your BIOS seems to not contain a fix for K8 errata #93\n"
	KERN_ERR "******* Working around it, but it may cause SEGVs or burn power.\n"
	KERN_ERR "******* Please consider a BIOS update.\n"
	KERN_ERR "******* Disabling USB legacy in the BIOS may also help.\n";

	/* Workaround for K8 erratum #93 & buggy BIOS.
	BIOS SMM functions are required to use a specific workaround
	to avoid corruption of the 64bit RIP register on C stepping K8.
	A lot of BIOS that didn't get tested properly miss this.
	The OS sees this as a page fault with the upper 32bits of RIP cleared.
	Try to work around it here.
	Note we only handle faults in kernel here. */

	static int is_errata93(struct pt_regs *regs, unsigned long address)
	{
	static int warned;
	if (address != regs->rip)
	return 0;
	if ((address >> 32) != 0)
	return 0;
	address \|= 0xffffffffUL << 32;
	if ((address >= (u64)_stext && address <= (u64)_etext) \|\|
	(address >= MODULES_VADDR && address <= MODULES_END)) {
	if (!warned) {
	printk(errata93_warning);
	warned = 1;
	}
	regs->rip = address;
	return 1;
	}
	return 0;
	}

	int unhandled_signal(struct task_struct *tsk, int sig)
	{
	if (tsk->pid == 1)
	return 1;
	/* Warn for strace, but not for gdb */
	if (!test_ti_thread_flag(tsk->thread_info, TIF_SYSCALL_TRACE) &&
	(tsk->ptrace & PT_PTRACED))
	return 0;
	return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_IGN) \|\|
	(tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
	}

	static noinline void pgtable_bad(unsigned long address, struct pt_regs *regs,
	unsigned long error_code)
	{
	oops_begin();
	printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
	current->comm, address);
	dump_pagetable(address);
	__die("Bad pagetable", regs, error_code);
	oops_end();
	do_exit(SIGKILL);
	}

	/*
	* Handle a fault on the vmalloc or module mapping area
	*/
	static int vmalloc_fault(unsigned long address)
	{
	pgd_t pgd, pgd_ref;
	pud_t pud, pud_ref;
	pmd_t pmd, pmd_ref;
	pte_t pte, pte_ref;

	/* Copy kernel mappings over when needed. This can also
	happen within a race in page table update. In the later
	case just flush. */

	pgd = pgd_offset(current->mm ?: &init_mm, address);
	pgd_ref = pgd_offset_k(address);
	if (pgd_none(*pgd_ref))
	return -1;
	if (pgd_none(*pgd))
	set_pgd(pgd, *pgd_ref);

	/* Below here mismatches are bugs because these lower tables
	are shared */

	pud = pud_offset(pgd, address);
	pud_ref = pud_offset(pgd_ref, address);
	if (pud_none(*pud_ref))
	return -1;
	if (pud_none(pud) \|\| pud_page(pud) != pud_page(*pud_ref))
	BUG();
	pmd = pmd_offset(pud, address);
	pmd_ref = pmd_offset(pud_ref, address);
	if (pmd_none(*pmd_ref))
	return -1;
	if (pmd_none(pmd) \|\| pmd_page(pmd) != pmd_page(*pmd_ref))
	BUG();
	pte_ref = pte_offset_kernel(pmd_ref, address);
	if (!pte_present(*pte_ref))
	return -1;
	pte = pte_offset_kernel(pmd, address);
	if (!pte_present(pte) \|\| pte_page(pte) != pte_page(*pte_ref))
	BUG();
	__flush_tlb_all();
	return 0;
	}

	int page_fault_trace = 0;
	int exception_trace = 1;

	/*
	* 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:
	* bit 0 == 0 means no page found, 1 means protection fault
	* bit 1 == 0 means read, 1 means write
	* bit 2 == 0 means kernel, 1 means user-mode
	* bit 3 == 1 means fault was an instruction fetch
	*/
	asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code)
	{
	struct task_struct *tsk;
	struct mm_struct *mm;
	struct vm_area_struct * vma;
	unsigned long address;
	const struct exception_table_entry *fixup;
	int write;
	siginfo_t info;

	#ifdef CONFIG_CHECKING
	{
	unsigned long gs;
	struct x8664_pda *pda = cpu_pda + stack_smp_processor_id();
	rdmsrl(MSR_GS_BASE, gs);
	if (gs != (unsigned long)pda) {
	wrmsrl(MSR_GS_BASE, pda);
	printk("page_fault: wrong gs %lx expected %p\n", gs, pda);
	}
	}
	#endif

	/* get the address */
	__asm__("movq %%cr2,%0":"=r" (address));
	if (notify_die(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
	SIGSEGV) == NOTIFY_STOP)
	return;

	if (likely(regs->eflags & X86_EFLAGS_IF))
	local_irq_enable();

	if (unlikely(page_fault_trace))
	printk("pagefault rip:%lx rsp:%lx cs:%lu ss:%lu address %lx error %lx\n",
	regs->rip,regs->rsp,regs->cs,regs->ss,address,error_code);

	tsk = current;
	mm = tsk->mm;
	info.si_code = SEGV_MAPERR;


	/*
	* We fault-in kernel-space virtual memory on-demand. The
	* 'reference' page table is init_mm.pgd.
	*
	* NOTE! We MUST NOT take any locks for this case. We may
	* be in an interrupt or a critical region, and should
	* only copy the information from the master page table,
	* nothing more.
	*
	* This verifies that the fault happens in kernel space
	* (error_code & 4) == 0, and that the fault was not a
	* protection error (error_code & 1) == 0.
	*/
	if (unlikely(address >= TASK_SIZE)) {
	if (!(error_code & 5)) {
	if (vmalloc_fault(address) < 0)
	goto bad_area_nosemaphore;
	return;
	}
	/*
	* Don't take the mm semaphore here. If we fixup a prefetch
	* fault we could otherwise deadlock.
	*/
	goto bad_area_nosemaphore;
	}

	if (unlikely(error_code & (1 << 3)))
	pgtable_bad(address, regs, error_code);

	/*
	* If we're in an interrupt or have no user
	* context, we must not take the fault..
	*/
	if (unlikely(in_atomic() \|\| !mm))
	goto bad_area_nosemaphore;

	again:
	/* 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. Unfortunatly, in the case of an
	* erroneous fault occuring 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 possibilty 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 ((error_code & 4) == 0 &&
	!search_exception_tables(regs->rip))
	goto bad_area_nosemaphore;
	down_read(&mm->mmap_sem);
	}

	vma = find_vma(mm, address);
	if (!vma)
	goto bad_area;
	if (likely(vma->vm_start <= address))
	goto good_area;
	if (!(vma->vm_flags & VM_GROWSDOWN))
	goto bad_area;
	if (error_code & 4) {
	// XXX: align red zone size with ABI
	if (address + 128 < regs->rsp)
	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:
	info.si_code = SEGV_ACCERR;
	write = 0;
	switch (error_code & 3) {
	default: /* 3: write, present */
	/* fall through */
	case 2: /* write, not present */
	if (!(vma->vm_flags & VM_WRITE))
	goto bad_area;
	write++;
	break;
	case 1: /* read, present */
	goto bad_area;
	case 0: /* read, not present */
	if (!(vma->vm_flags & (VM_READ \| VM_EXEC)))
	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.
	*/
	switch (handle_mm_fault(mm, vma, address, write)) {
	case 1:
	tsk->min_flt++;
	break;
	case 2:
	tsk->maj_flt++;
	break;
	case 0:
	goto do_sigbus;
	default:
	goto out_of_memory;
	}

	up_read(&mm->mmap_sem);
	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);

	bad_area_nosemaphore:

	#ifdef CONFIG_IA32_EMULATION
	/* 32bit vsyscall. map on demand. */
	if (test_thread_flag(TIF_IA32) &&
	address >= VSYSCALL32_BASE && address < VSYSCALL32_END) {
	if (map_syscall32(mm, address) < 0)
	goto out_of_memory2;
	return;
	}
	#endif

	/* User mode accesses just cause a SIGSEGV */
	if (error_code & 4) {
	if (is_prefetch(regs, address, error_code))
	return;

	/* Work around K8 erratum #100 K8 in compat mode
	occasionally jumps to illegal addresses >4GB. We
	catch this here in the page fault handler because
	these addresses are not reachable. Just detect this
	case and return. Any code segment in LDT is
	compatibility mode. */
	if ((regs->cs == __USER32_CS \|\| (regs->cs & (1<<2))) &&
	(address >> 32))
	return;

	if (exception_trace && unhandled_signal(tsk, SIGSEGV)) {
	printk(
	"%s%s[%d]: segfault at %016lx rip %016lx rsp %016lx error %lx\n",
	tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
	tsk->comm, tsk->pid, address, regs->rip,
	regs->rsp, error_code);
	}

	tsk->thread.cr2 = address;
	/* Kernel addresses are always protection faults */
	tsk->thread.error_code = error_code \| (address >= TASK_SIZE);
	tsk->thread.trap_no = 14;
	info.si_signo = SIGSEGV;
	info.si_errno = 0;
	/* info.si_code has been set above */
	info.si_addr = (void __user *)address;
	force_sig_info(SIGSEGV, &info, tsk);
	return;
	}

	no_context:

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

	/*
	* Hall of shame of CPU/BIOS bugs.
	*/

	if (is_prefetch(regs, address, error_code))
	return;

	if (is_errata93(regs, address))
	return;

	/*
	* Oops. The kernel tried to access some bad page. We'll have to
	* terminate things with extreme prejudice.
	*/

	oops_begin();

	if (address < PAGE_SIZE)
	printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
	else
	printk(KERN_ALERT "Unable to handle kernel paging request");
	printk(" at %016lx RIP: \n" KERN_ALERT,address);
	printk_address(regs->rip);
	printk("\n");
	dump_pagetable(address);
	__die("Oops", regs, error_code);
	/* Executive summary in case the body of the oops scrolled away */
	printk(KERN_EMERG "CR2: %016lx\n", address);
	oops_end();
	do_exit(SIGKILL);

	/*
	* We ran out of memory, or some other thing happened to us that made
	* us unable to handle the page fault gracefully.
	*/
	out_of_memory:
	up_read(&mm->mmap_sem);
	out_of_memory2:
	if (current->pid == 1) {
	yield();
	goto again;
	}
	printk("VM: killing process %s\n", tsk->comm);
	if (error_code & 4)
	do_exit(SIGKILL);
	goto no_context;

	do_sigbus:
	up_read(&mm->mmap_sem);

	/* Kernel mode? Handle exceptions or die */
	if (!(error_code & 4))
	goto no_context;

	tsk->thread.cr2 = address;
	tsk->thread.error_code = error_code;
	tsk->thread.trap_no = 14;
	info.si_signo = SIGBUS;
	info.si_errno = 0;
	info.si_code = BUS_ADRERR;
	info.si_addr = (void __user *)address;
	force_sig_info(SIGBUS, &info, tsk);
	return;
	}