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