Fix common misspellings
[linux-2.6.git] / arch / arm / kernel / swp_emulate.c
1 /*
2  *  linux/arch/arm/kernel/swp_emulate.c
3  *
4  *  Copyright (C) 2009 ARM Limited
5  *  __user_* functions adapted from include/asm/uaccess.h
6  *
7  * This program is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License version 2 as
9  * published by the Free Software Foundation.
10  *
11  *  Implements emulation of the SWP/SWPB instructions using load-exclusive and
12  *  store-exclusive for processors that have them disabled (or future ones that
13  *  might not implement them).
14  *
15  *  Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
16  *  Where: Rt  = destination
17  *         Rt2 = source
18  *         Rn  = address
19  */
20
21 #include <linux/init.h>
22 #include <linux/kernel.h>
23 #include <linux/proc_fs.h>
24 #include <linux/sched.h>
25 #include <linux/syscalls.h>
26 #include <linux/perf_event.h>
27
28 #include <asm/traps.h>
29 #include <asm/uaccess.h>
30
31 /*
32  * Error-checking SWP macros implemented using ldrex{b}/strex{b}
33  */
34 #define __user_swpX_asm(data, addr, res, temp, B)               \
35         __asm__ __volatile__(                                   \
36         "       mov             %2, %1\n"                       \
37         "0:     ldrex"B"        %1, [%3]\n"                     \
38         "1:     strex"B"        %0, %2, [%3]\n"                 \
39         "       cmp             %0, #0\n"                       \
40         "       movne           %0, %4\n"                       \
41         "2:\n"                                                  \
42         "       .section         .fixup,\"ax\"\n"               \
43         "       .align          2\n"                            \
44         "3:     mov             %0, %5\n"                       \
45         "       b               2b\n"                           \
46         "       .previous\n"                                    \
47         "       .section         __ex_table,\"a\"\n"            \
48         "       .align          3\n"                            \
49         "       .long           0b, 3b\n"                       \
50         "       .long           1b, 3b\n"                       \
51         "       .previous"                                      \
52         : "=&r" (res), "+r" (data), "=&r" (temp)                \
53         : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT)              \
54         : "cc", "memory")
55
56 #define __user_swp_asm(data, addr, res, temp) \
57         __user_swpX_asm(data, addr, res, temp, "")
58 #define __user_swpb_asm(data, addr, res, temp) \
59         __user_swpX_asm(data, addr, res, temp, "b")
60
61 /*
62  * Macros/defines for extracting register numbers from instruction.
63  */
64 #define EXTRACT_REG_NUM(instruction, offset) \
65         (((instruction) & (0xf << (offset))) >> (offset))
66 #define RN_OFFSET  16
67 #define RT_OFFSET  12
68 #define RT2_OFFSET  0
69 /*
70  * Bit 22 of the instruction encoding distinguishes between
71  * the SWP and SWPB variants (bit set means SWPB).
72  */
73 #define TYPE_SWPB (1 << 22)
74
75 static unsigned long swpcounter;
76 static unsigned long swpbcounter;
77 static unsigned long abtcounter;
78 static pid_t         previous_pid;
79
80 #ifdef CONFIG_PROC_FS
81 static int proc_read_status(char *page, char **start, off_t off, int count,
82                             int *eof, void *data)
83 {
84         char *p = page;
85         int len;
86
87         p += sprintf(p, "Emulated SWP:\t\t%lu\n", swpcounter);
88         p += sprintf(p, "Emulated SWPB:\t\t%lu\n", swpbcounter);
89         p += sprintf(p, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
90         if (previous_pid != 0)
91                 p += sprintf(p, "Last process:\t\t%d\n", previous_pid);
92
93         len = (p - page) - off;
94         if (len < 0)
95                 len = 0;
96
97         *eof = (len <= count) ? 1 : 0;
98         *start = page + off;
99
100         return len;
101 }
102 #endif
103
104 /*
105  * Set up process info to signal segmentation fault - called on access error.
106  */
107 static void set_segfault(struct pt_regs *regs, unsigned long addr)
108 {
109         siginfo_t info;
110
111         if (find_vma(current->mm, addr) == NULL)
112                 info.si_code = SEGV_MAPERR;
113         else
114                 info.si_code = SEGV_ACCERR;
115
116         info.si_signo = SIGSEGV;
117         info.si_errno = 0;
118         info.si_addr  = (void *) instruction_pointer(regs);
119
120         pr_debug("SWP{B} emulation: access caused memory abort!\n");
121         arm_notify_die("Illegal memory access", regs, &info, 0, 0);
122
123         abtcounter++;
124 }
125
126 static int emulate_swpX(unsigned int address, unsigned int *data,
127                         unsigned int type)
128 {
129         unsigned int res = 0;
130
131         if ((type != TYPE_SWPB) && (address & 0x3)) {
132                 /* SWP to unaligned address not permitted */
133                 pr_debug("SWP instruction on unaligned pointer!\n");
134                 return -EFAULT;
135         }
136
137         while (1) {
138                 unsigned long temp;
139
140                 /*
141                  * Barrier required between accessing protected resource and
142                  * releasing a lock for it. Legacy code might not have done
143                  * this, and we cannot determine that this is not the case
144                  * being emulated, so insert always.
145                  */
146                 smp_mb();
147
148                 if (type == TYPE_SWPB)
149                         __user_swpb_asm(*data, address, res, temp);
150                 else
151                         __user_swp_asm(*data, address, res, temp);
152
153                 if (likely(res != -EAGAIN) || signal_pending(current))
154                         break;
155
156                 cond_resched();
157         }
158
159         if (res == 0) {
160                 /*
161                  * Barrier also required between acquiring a lock for a
162                  * protected resource and accessing the resource. Inserted for
163                  * same reason as above.
164                  */
165                 smp_mb();
166
167                 if (type == TYPE_SWPB)
168                         swpbcounter++;
169                 else
170                         swpcounter++;
171         }
172
173         return res;
174 }
175
176 /*
177  * swp_handler logs the id of calling process, dissects the instruction, sanity
178  * checks the memory location, calls emulate_swpX for the actual operation and
179  * deals with fixup/error handling before returning
180  */
181 static int swp_handler(struct pt_regs *regs, unsigned int instr)
182 {
183         unsigned int address, destreg, data, type;
184         unsigned int res = 0;
185
186         perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, 0, regs, regs->ARM_pc);
187
188         if (current->pid != previous_pid) {
189                 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
190                          current->comm, (unsigned long)current->pid);
191                 previous_pid = current->pid;
192         }
193
194         address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
195         data    = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
196         destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
197
198         type = instr & TYPE_SWPB;
199
200         pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
201                  EXTRACT_REG_NUM(instr, RN_OFFSET), address,
202                  destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
203
204         /* Check access in reasonable access range for both SWP and SWPB */
205         if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
206                 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
207                          (void *)address);
208                 res = -EFAULT;
209         } else {
210                 res = emulate_swpX(address, &data, type);
211         }
212
213         if (res == 0) {
214                 /*
215                  * On successful emulation, revert the adjustment to the PC
216                  * made in kernel/traps.c in order to resume execution at the
217                  * instruction following the SWP{B}.
218                  */
219                 regs->ARM_pc += 4;
220                 regs->uregs[destreg] = data;
221         } else if (res == -EFAULT) {
222                 /*
223                  * Memory errors do not mean emulation failed.
224                  * Set up signal info to return SEGV, then return OK
225                  */
226                 set_segfault(regs, address);
227         }
228
229         return 0;
230 }
231
232 /*
233  * Only emulate SWP/SWPB executed in ARM state/User mode.
234  * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
235  */
236 static struct undef_hook swp_hook = {
237         .instr_mask = 0x0fb00ff0,
238         .instr_val  = 0x01000090,
239         .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
240         .cpsr_val   = USR_MODE,
241         .fn         = swp_handler
242 };
243
244 /*
245  * Register handler and create status file in /proc/cpu
246  * Invoked as late_initcall, since not needed before init spawned.
247  */
248 static int __init swp_emulation_init(void)
249 {
250 #ifdef CONFIG_PROC_FS
251         struct proc_dir_entry *res;
252
253         res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL);
254
255         if (!res)
256                 return -ENOMEM;
257
258         res->read_proc = proc_read_status;
259 #endif /* CONFIG_PROC_FS */
260
261         printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
262         register_undef_hook(&swp_hook);
263
264         return 0;
265 }
266
267 late_initcall(swp_emulation_init);