arch/microblaze/mm/fault.c

   1 /*
   2  *  arch/microblaze/mm/fault.c
   3  *
   4  *    Copyright (C) 2007 Xilinx, Inc.  All rights reserved.
   5  *
   6  *  Derived from "arch/ppc/mm/fault.c"
   7  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
   8  *
   9  *  Derived from "arch/i386/mm/fault.c"
  10  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  11  *
  12  *  Modified by Cort Dougan and Paul Mackerras.
  13  *
  14  * This file is subject to the terms and conditions of the GNU General
  15  * Public License.  See the file COPYING in the main directory of this
  16  * archive for more details.
  17  *
  18  */
  19
  20 #include <linux/module.h>
  21 #include <linux/signal.h>
  22 #include <linux/sched.h>
  23 #include <linux/kernel.h>
  24 #include <linux/errno.h>
  25 #include <linux/string.h>
  26 #include <linux/types.h>
  27 #include <linux/ptrace.h>
  28 #include <linux/mman.h>
  29 #include <linux/mm.h>
  30 #include <linux/interrupt.h>
  31
  32 #include <asm/page.h>
  33 #include <asm/pgtable.h>
  34 #include <asm/mmu.h>
  35 #include <asm/mmu_context.h>
  36 #include <asm/system.h>
  37 #include <linux/uaccess.h>
  38 #include <asm/exceptions.h>
  39
  40 #if defined(CONFIG_KGDB)
  41 int debugger_kernel_faults = 1;
  42 #endif
  43
  44 static unsigned long pte_misses;        /* updated by do_page_fault() */
  45 static unsigned long pte_errors;        /* updated by do_page_fault() */
  46
  47 /*
  48  * Check whether the instruction at regs->pc is a store using
  49  * an update addressing form which will update r1.
  50  */
  51 static int store_updates_sp(struct pt_regs *regs)
  52 {
  53         unsigned int inst;
  54
  55         if (get_user(inst, (unsigned int *)regs->pc))
  56                 return 0;
  57         /* check for 1 in the rD field */
  58         if (((inst >> 21) & 0x1f) != 1)
  59                 return 0;
  60         /* check for store opcodes */
  61         if ((inst & 0xd0000000) == 0xd0000000)
  62                 return 1;
  63         return 0;
  64 }
  65
  66
  67 /*
  68  * bad_page_fault is called when we have a bad access from the kernel.
  69  * It is called from do_page_fault above and from some of the procedures
  70  * in traps.c.
  71  */
  72 static void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
  73 {
  74         const struct exception_table_entry *fixup;
  75 /* MS: no context */
  76         /* Are we prepared to handle this fault?  */
  77         fixup = search_exception_tables(regs->pc);
  78         if (fixup) {
  79                 regs->pc = fixup->fixup;
  80                 return;
  81         }
  82
  83         /* kernel has accessed a bad area */
  84 #if defined(CONFIG_KGDB)
  85         if (debugger_kernel_faults)
  86                 debugger(regs);
  87 #endif
  88         die("kernel access of bad area", regs, sig);
  89 }
  90
  91 /*
  92  * The error_code parameter is ESR for a data fault,
  93  * 0 for an instruction fault.
  94  */
  95 void do_page_fault(struct pt_regs *regs, unsigned long address,
  96                    unsigned long error_code)
  97 {
  98         struct vm_area_struct *vma;
  99         struct mm_struct *mm = current->mm;
 100         siginfo_t info;
 101         int code = SEGV_MAPERR;
 102         int is_write = error_code & ESR_S;
 103         int fault;
 104
 105         regs->ear = address;
 106         regs->esr = error_code;
 107
 108         /* On a kernel SLB miss we can only check for a valid exception entry */
 109         if (kernel_mode(regs) && (address >= TASK_SIZE)) {
 110                 printk(KERN_WARNING "kernel task_size exceed");
 111                 _exception(SIGSEGV, regs, code, address);
 112         }
 113
 114         /* for instr TLB miss and instr storage exception ESR_S is undefined */
 115         if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11)
 116                 is_write = 0;
 117
 118 #if defined(CONFIG_KGDB)
 119         if (debugger_fault_handler && regs->trap == 0x300) {
 120                 debugger_fault_handler(regs);
 121                 return;
 122         }
 123 #endif /* CONFIG_KGDB */
 124
 125         if (in_atomic() || mm == NULL) {
 126                 /* FIXME */
 127                 if (kernel_mode(regs)) {
 128                         printk(KERN_EMERG
 129                                 "Page fault in kernel mode - Oooou!!! pid %d\n",
 130                                 current->pid);
 131                         _exception(SIGSEGV, regs, code, address);
 132                         return;
 133                 }
 134                 /* in_atomic() in user mode is really bad,
 135                    as is current->mm == NULL. */
 136                 printk(KERN_EMERG "Page fault in user mode with "
 137                        "in_atomic(), mm = %p\n", mm);
 138                 printk(KERN_EMERG "r15 = %lx  MSR = %lx\n",
 139                        regs->r15, regs->msr);
 140                 die("Weird page fault", regs, SIGSEGV);
 141         }
 142
 143         /* When running in the kernel we expect faults to occur only to
 144          * addresses in user space.  All other faults represent errors in the
 145          * kernel and should generate an OOPS.  Unfortunately, in the case of an
 146          * erroneous fault occurring in a code path which already holds mmap_sem
 147          * we will deadlock attempting to validate the fault against the
 148          * address space.  Luckily the kernel only validly references user
 149          * space from well defined areas of code, which are listed in the
 150          * exceptions table.
 151          *
 152          * As the vast majority of faults will be valid we will only perform
 153          * the source reference check when there is a possibility of a deadlock.
 154          * Attempt to lock the address space, if we cannot we then validate the
 155          * source.  If this is invalid we can skip the address space check,
 156          * thus avoiding the deadlock.
 157          */
 158         if (!down_read_trylock(&mm->mmap_sem)) {
 159                 if (kernel_mode(regs) && !search_exception_tables(regs->pc))
 160                         goto bad_area_nosemaphore;
 161
 162                 down_read(&mm->mmap_sem);
 163         }
 164
 165         vma = find_vma(mm, address);
 166         if (!vma)
 167                 goto bad_area;
 168
 169         if (vma->vm_start <= address)
 170                 goto good_area;
 171
 172         if (!(vma->vm_flags & VM_GROWSDOWN))
 173                 goto bad_area;
 174
 175         if (!is_write)
 176                 goto bad_area;
 177
 178         /*
 179          * N.B. The ABI allows programs to access up to
 180          * a few hundred bytes below the stack pointer (TBD).
 181          * The kernel signal delivery code writes up to about 1.5kB
 182          * below the stack pointer (r1) before decrementing it.
 183          * The exec code can write slightly over 640kB to the stack
 184          * before setting the user r1.  Thus we allow the stack to
 185          * expand to 1MB without further checks.
 186          */
 187         if (address + 0x100000 < vma->vm_end) {
 188
 189                 /* get user regs even if this fault is in kernel mode */
 190                 struct pt_regs *uregs = current->thread.regs;
 191                 if (uregs == NULL)
 192                         goto bad_area;
 193
 194                 /*
 195                  * A user-mode access to an address a long way below
 196                  * the stack pointer is only valid if the instruction
 197                  * is one which would update the stack pointer to the
 198                  * address accessed if the instruction completed,
 199                  * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
 200                  * (or the byte, halfword, float or double forms).
 201                  *
 202                  * If we don't check this then any write to the area
 203                  * between the last mapped region and the stack will
 204                  * expand the stack rather than segfaulting.
 205                  */
 206                 if (address + 2048 < uregs->r1
 207                         && (kernel_mode(regs) || !store_updates_sp(regs)))
 208                                 goto bad_area;
 209         }
 210         if (expand_stack(vma, address))
 211                 goto bad_area;
 212
 213 good_area:
 214         code = SEGV_ACCERR;
 215
 216         /* a write */
 217         if (is_write) {
 218                 if (!(vma->vm_flags & VM_WRITE))
 219                         goto bad_area;
 220         /* a read */
 221         } else {
 222                 /* protection fault */
 223                 if (error_code & 0x08000000)
 224                         goto bad_area;
 225                 if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
 226                         goto bad_area;
 227         }
 228
 229         /*
 230          * If for any reason at all we couldn't handle the fault,
 231          * make sure we exit gracefully rather than endlessly redo
 232          * the fault.
 233          */
 234 survive:
 235         fault = handle_mm_fault(mm, vma, address, is_write);
 236         if (unlikely(fault & VM_FAULT_ERROR)) {
 237                 if (fault & VM_FAULT_OOM)
 238                         goto out_of_memory;
 239                 else if (fault & VM_FAULT_SIGBUS)
 240                         goto do_sigbus;
 241                 BUG();
 242         }
 243         if (fault & VM_FAULT_MAJOR)
 244                 current->maj_flt++;
 245         else
 246                 current->min_flt++;
 247         up_read(&mm->mmap_sem);
 248         /*
 249          * keep track of tlb+htab misses that are good addrs but
 250          * just need pte's created via handle_mm_fault()
 251          * -- Cort
 252          */
 253         pte_misses++;
 254         return;
 255
 256 bad_area:
 257         up_read(&mm->mmap_sem);
 258
 259 bad_area_nosemaphore:
 260         pte_errors++;
 261
 262         /* User mode accesses cause a SIGSEGV */
 263         if (user_mode(regs)) {
 264                 _exception(SIGSEGV, regs, code, address);
 265 /*              info.si_signo = SIGSEGV;
 266                 info.si_errno = 0;
 267                 info.si_code = code;
 268                 info.si_addr = (void *) address;
 269                 force_sig_info(SIGSEGV, &info, current);*/
 270                 return;
 271         }
 272
 273         bad_page_fault(regs, address, SIGSEGV);
 274         return;
 275
 276 /*
 277  * We ran out of memory, or some other thing happened to us that made
 278  * us unable to handle the page fault gracefully.
 279  */
 280 out_of_memory:
 281         if (current->pid == 1) {
 282                 yield();
 283                 down_read(&mm->mmap_sem);
 284                 goto survive;
 285         }
 286         up_read(&mm->mmap_sem);
 287         printk(KERN_WARNING "VM: killing process %s\n", current->comm);
 288         if (user_mode(regs))
 289                 do_exit(SIGKILL);
 290         bad_page_fault(regs, address, SIGKILL);
 291         return;
 292
 293 do_sigbus:
 294         up_read(&mm->mmap_sem);
 295         if (user_mode(regs)) {
 296                 info.si_signo = SIGBUS;
 297                 info.si_errno = 0;
 298                 info.si_code = BUS_ADRERR;
 299                 info.si_addr = (void __user *)address;
 300                 force_sig_info(SIGBUS, &info, current);
 301                 return;
 302         }
 303         bad_page_fault(regs, address, SIGBUS);
 304 }