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fault.c

/*
 *  arch/s390/mm/fault.c
 *
 *  S390 version
 *    Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
 *    Author(s): Hartmut Penner (hp@de.ibm.com)
 *               Ulrich Weigand (uweigand@de.ibm.com)
 *
 *  Derived from "arch/i386/mm/fault.c"
 *    Copyright (C) 1995  Linus Torvalds
 */

#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/kdebug.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/console.h>
#include <linux/module.h>
#include <linux/hardirq.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>

#include <asm/system.h>
#include <asm/pgtable.h>
#include <asm/s390_ext.h>

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

#ifdef CONFIG_SYSCTL
extern int sysctl_userprocess_debug;
#endif

extern void die(const char *,struct pt_regs *,long);

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

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

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


/*
 * Unlock any spinlocks which will prevent us from getting the
 * message out.
 */
void bust_spinlocks(int yes)
{
      if (yes) {
            oops_in_progress = 1;
      } else {
            int loglevel_save = console_loglevel;
            console_unblank();
            oops_in_progress = 0;
            /*
             * OK, the message is on the console.  Now we call printk()
             * without oops_in_progress set so that printk will give klogd
             * a poke.  Hold onto your hats...
             */
            console_loglevel = 15;
            printk(" ");
            console_loglevel = loglevel_save;
      }
}

/*
 * Returns the address space associated with the fault.
 * Returns 0 for kernel space, 1 for user space and
 * 2 for code execution in user space with noexec=on.
 */
static inline int check_space(struct task_struct *tsk)
{
      /*
       * The lowest two bits of S390_lowcore.trans_exc_code
       * indicate which paging table was used.
       */
      int desc = S390_lowcore.trans_exc_code & 3;

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

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

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

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

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

      /*
       * Oops. The kernel tried to access some bad page. We'll have to
       * terminate things with extreme prejudice.
       */
      if (check_space(current) == 0)
            printk(KERN_ALERT "Unable to handle kernel pointer dereference"
                   " at virtual kernel address %p\n", (void *)address);
      else
            printk(KERN_ALERT "Unable to handle kernel paging request"
                   " at virtual user address %p\n", (void *)address);

      die("Oops", regs, error_code);
      do_exit(SIGKILL);
}

static void do_low_address(struct pt_regs *regs, unsigned long error_code)
{
      /* Low-address protection hit in kernel mode means
         NULL pointer write access in kernel mode.  */
      if (regs->psw.mask & PSW_MASK_PSTATE) {
            /* Low-address protection hit in user mode 'cannot happen'. */
            die ("Low-address protection", regs, error_code);
            do_exit(SIGKILL);
      }

      do_no_context(regs, error_code, 0);
}

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
static int do_out_of_memory(struct pt_regs *regs, unsigned long error_code,
                      unsigned long address)
{
      struct task_struct *tsk = current;
      struct mm_struct *mm = tsk->mm;

      up_read(&mm->mmap_sem);
      if (is_global_init(tsk)) {
            yield();
            down_read(&mm->mmap_sem);
            return 1;
      }
      printk("VM: killing process %s\n", tsk->comm);
      if (regs->psw.mask & PSW_MASK_PSTATE)
            do_group_exit(SIGKILL);
      do_no_context(regs, error_code, address);
      return 0;
}

static void do_sigbus(struct pt_regs *regs, unsigned long error_code,
                  unsigned long address)
{
      struct task_struct *tsk = current;
      struct mm_struct *mm = tsk->mm;

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

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

#ifdef CONFIG_S390_EXEC_PROTECT
extern long sys_sigreturn(struct pt_regs *regs);
extern long sys_rt_sigreturn(struct pt_regs *regs);
extern long sys32_sigreturn(struct pt_regs *regs);
extern long sys32_rt_sigreturn(struct pt_regs *regs);

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

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

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

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * error_code:
 *   04       Protection           ->  Write-Protection  (suprression)
 *   10       Segment translation  ->  Not present       (nullification)
 *   11       Page translation     ->  Not present       (nullification)
 *   3b       Region third trans.  ->  Not present       (nullification)
 */
static inline void
do_exception(struct pt_regs *regs, unsigned long error_code, int write)
{
      struct task_struct *tsk;
      struct mm_struct *mm;
      struct vm_area_struct *vma;
      unsigned long address;
      int space;
      int si_code;
      int fault;

      if (notify_page_fault(regs, error_code))
            return;

      tsk = current;
      mm = tsk->mm;

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

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

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

      down_read(&mm->mmap_sem);

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

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

      if (vma->vm_start <= address)
            goto good_area;
      if (!(vma->vm_flags & VM_GROWSDOWN))
            goto bad_area;
      if (expand_stack(vma, address))
            goto bad_area;
/*
 * Ok, we have a good vm_area for this memory access, so
 * we can handle it..
 */
good_area:
      si_code = SEGV_ACCERR;
      if (!write) {
            /* page not present, check vm flags */
            if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                  goto bad_area;
      } else {
            if (!(vma->vm_flags & VM_WRITE))
                  goto bad_area;
      }

survive:
      /*
       * If for any reason at all we couldn't handle the fault,
       * make sure we exit gracefully rather than endlessly redo
       * the fault.
       */
      fault = handle_mm_fault(mm, vma, address, write);
      if (unlikely(fault & VM_FAULT_ERROR)) {
            if (fault & VM_FAULT_OOM) {
                  if (do_out_of_memory(regs, error_code, address))
                        goto survive;
                  return;
            } else if (fault & VM_FAULT_SIGBUS) {
                  do_sigbus(regs, error_code, address);
                  return;
            }
            BUG();
      }
      if (fault & VM_FAULT_MAJOR)
            tsk->maj_flt++;
      else
            tsk->min_flt++;

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

/*
 * Something tried to access memory that isn't in our memory map..
 * Fix it, but check if it's kernel or user first..
 */
bad_area:
      up_read(&mm->mmap_sem);

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

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

void __kprobes do_protection_exception(struct pt_regs *regs,
                               unsigned long error_code)
{
      /* Protection exception is supressing, decrement psw address. */
      regs->psw.addr -= (error_code >> 16);
      /*
       * Check for low-address protection.  This needs to be treated
       * as a special case because the translation exception code
       * field is not guaranteed to contain valid data in this case.
       */
      if (unlikely(!(S390_lowcore.trans_exc_code & 4))) {
            do_low_address(regs, error_code);
            return;
      }
      do_exception(regs, 4, 1);
}

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

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

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

__setup("nopfault", nopfault);

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

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

      if (!MACHINE_IS_VM || pfault_disable)
            return -1;
      asm volatile(
            "     diag  %1,%0,0x258\n"
            "0:   j     2f\n"
            "1:   la    %0,8\n"
            "2:\n"
            EX_TABLE(0b,1b)
            : "=d" (rc) : "a" (&refbk), "m" (refbk) : "cc");
        __ctl_set_bit(0, 9);
        return rc;
}

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

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

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

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

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

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

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

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

      if (pfault_init() == 0)
            return;

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

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