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 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 (unlikely(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 (unlikely(in_atomic() || !mm)) {
 126                 if (kernel_mode(regs))
 127                         goto bad_area_nosemaphore;
 128
 129                 /* in_atomic() in user mode is really bad,
 130                    as is current->mm == NULL. */
 131                 printk(KERN_EMERG "Page fault in user mode with "
 132                        "in_atomic(), mm = %p\n", mm);
 133                 printk(KERN_EMERG "r15 = %lx  MSR = %lx\n",
 134                        regs->r15, regs->msr);
 135                 die("Weird page fault", regs, SIGSEGV);
 136         }
 137
 138         /* When running in the kernel we expect faults to occur only to
 139          * addresses in user space.  All other faults represent errors in the
 140          * kernel and should generate an OOPS.  Unfortunately, in the case of an
 141          * erroneous fault occurring in a code path which already holds mmap_sem
 142          * we will deadlock attempting to validate the fault against the
 143          * address space.  Luckily the kernel only validly references user
 144          * space from well defined areas of code, which are listed in the
 145          * exceptions table.
 146          *
 147          * As the vast majority of faults will be valid we will only perform
 148          * the source reference check when there is a possibility of a deadlock.
 149          * Attempt to lock the address space, if we cannot we then validate the
 150          * source.  If this is invalid we can skip the address space check,
 151          * thus avoiding the deadlock.
 152          */
 153         if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
 154                 if (kernel_mode(regs) && !search_exception_tables(regs->pc))
 155                         goto bad_area_nosemaphore;
 156
 157                 down_read(&mm->mmap_sem);
 158         }
 159
 160         vma = find_vma(mm, address);
 161         if (unlikely(!vma))
 162                 goto bad_area;
 163
 164         if (vma->vm_start <= address)
 165                 goto good_area;
 166
 167         if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
 168                 goto bad_area;
 169
 170         if (unlikely(!is_write))
 171                 goto bad_area;
 172
 173         /*
 174          * N.B. The ABI allows programs to access up to
 175          * a few hundred bytes below the stack pointer (TBD).
 176          * The kernel signal delivery code writes up to about 1.5kB
 177          * below the stack pointer (r1) before decrementing it.
 178          * The exec code can write slightly over 640kB to the stack
 179          * before setting the user r1.  Thus we allow the stack to
 180          * expand to 1MB without further checks.
 181          */
 182         if (unlikely(address + 0x100000 < vma->vm_end)) {
 183
 184                 /* get user regs even if this fault is in kernel mode */
 185                 struct pt_regs *uregs = current->thread.regs;
 186                 if (uregs == NULL)
 187                         goto bad_area;
 188
 189                 /*
 190                  * A user-mode access to an address a long way below
 191                  * the stack pointer is only valid if the instruction
 192                  * is one which would update the stack pointer to the
 193                  * address accessed if the instruction completed,
 194                  * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
 195                  * (or the byte, halfword, float or double forms).
 196                  *
 197                  * If we don't check this then any write to the area
 198                  * between the last mapped region and the stack will
 199                  * expand the stack rather than segfaulting.
 200                  */
 201                 if (address + 2048 < uregs->r1
 202                         && (kernel_mode(regs) || !store_updates_sp(regs)))
 203                                 goto bad_area;
 204         }
 205         if (expand_stack(vma, address))
 206                 goto bad_area;
 207
 208 good_area:
 209         code = SEGV_ACCERR;
 210
 211         /* a write */
 212         if (unlikely(is_write)) {
 213                 if (unlikely(!(vma->vm_flags & VM_WRITE)))
 214                         goto bad_area;
 215         /* a read */
 216         } else {
 217                 /* protection fault */
 218                 if (unlikely(error_code & 0x08000000))
 219                         goto bad_area;
 220                 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC))))
 221                         goto bad_area;
 222         }
 223
 224         /*
 225          * If for any reason at all we couldn't handle the fault,
 226          * make sure we exit gracefully rather than endlessly redo
 227          * the fault.
 228          */
 229 survive:
 230         fault = handle_mm_fault(mm, vma, address, is_write ? FAULT_FLAG_WRITE : 0);
 231         if (unlikely(fault & VM_FAULT_ERROR)) {
 232                 if (fault & VM_FAULT_OOM)
 233                         goto out_of_memory;
 234                 else if (fault & VM_FAULT_SIGBUS)
 235                         goto do_sigbus;
 236                 BUG();
 237         }
 238         if (unlikely(fault & VM_FAULT_MAJOR))
 239                 current->maj_flt++;
 240         else
 241                 current->min_flt++;
 242         up_read(&mm->mmap_sem);
 243         /*
 244          * keep track of tlb+htab misses that are good addrs but
 245          * just need pte's created via handle_mm_fault()
 246          * -- Cort
 247          */
 248         pte_misses++;
 249         return;
 250
 251 bad_area:
 252         up_read(&mm->mmap_sem);
 253
 254 bad_area_nosemaphore:
 255         pte_errors++;
 256
 257         /* User mode accesses cause a SIGSEGV */
 258         if (user_mode(regs)) {
 259                 _exception(SIGSEGV, regs, code, address);
 260 /*              info.si_signo = SIGSEGV;
 261                 info.si_errno = 0;
 262                 info.si_code = code;
 263                 info.si_addr = (void *) address;
 264                 force_sig_info(SIGSEGV, &info, current);*/
 265                 return;
 266         }
 267
 268         bad_page_fault(regs, address, SIGSEGV);
 269         return;
 270
 271 /*
 272  * We ran out of memory, or some other thing happened to us that made
 273  * us unable to handle the page fault gracefully.
 274  */
 275 out_of_memory:
 276         up_read(&mm->mmap_sem);
 277         if (!user_mode(regs))
 278                 bad_page_fault(regs, address, SIGKILL);
 279         else
 280                 pagefault_out_of_memory();
 281         return;
 282
 283 do_sigbus:
 284         up_read(&mm->mmap_sem);
 285         if (user_mode(regs)) {
 286                 info.si_signo = SIGBUS;
 287                 info.si_errno = 0;
 288                 info.si_code = BUS_ADRERR;
 289                 info.si_addr = (void __user *)address;
 290                 force_sig_info(SIGBUS, &info, current);
 291                 return;
 292         }
 293         bad_page_fault(regs, address, SIGBUS);
 294 }