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1 | /* |
2 | * ARMv8 single-step debug support and mdscr context switching. | |
3 | * | |
4 | * Copyright (C) 2012 ARM Limited | |
5 | * | |
6 | * This program is free software; you can redistribute it and/or modify | |
7 | * it under the terms of the GNU General Public License version 2 as | |
8 | * published by the Free Software Foundation. | |
9 | * | |
10 | * This program is distributed in the hope that it will be useful, | |
11 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | * GNU General Public License for more details. | |
14 | * | |
15 | * You should have received a copy of the GNU General Public License | |
16 | * along with this program. If not, see <http://www.gnu.org/licenses/>. | |
17 | * | |
18 | * Author: Will Deacon <will.deacon@arm.com> | |
19 | */ | |
20 | ||
21 | #include <linux/cpu.h> | |
22 | #include <linux/debugfs.h> | |
23 | #include <linux/hardirq.h> | |
24 | #include <linux/init.h> | |
25 | #include <linux/ptrace.h> | |
26 | #include <linux/stat.h> | |
27 | ||
28 | #include <asm/debug-monitors.h> | |
29 | #include <asm/local.h> | |
30 | #include <asm/cputype.h> | |
31 | #include <asm/system_misc.h> | |
32 | ||
33 | /* Low-level stepping controls. */ | |
34 | #define DBG_MDSCR_SS (1 << 0) | |
35 | #define DBG_SPSR_SS (1 << 21) | |
36 | ||
37 | /* MDSCR_EL1 enabling bits */ | |
38 | #define DBG_MDSCR_KDE (1 << 13) | |
39 | #define DBG_MDSCR_MDE (1 << 15) | |
40 | #define DBG_MDSCR_MASK ~(DBG_MDSCR_KDE | DBG_MDSCR_MDE) | |
41 | ||
42 | /* Determine debug architecture. */ | |
43 | u8 debug_monitors_arch(void) | |
44 | { | |
45 | return read_cpuid(ID_AA64DFR0_EL1) & 0xf; | |
46 | } | |
47 | ||
48 | /* | |
49 | * MDSCR access routines. | |
50 | */ | |
51 | static void mdscr_write(u32 mdscr) | |
52 | { | |
53 | unsigned long flags; | |
54 | local_dbg_save(flags); | |
55 | asm volatile("msr mdscr_el1, %0" :: "r" (mdscr)); | |
56 | local_dbg_restore(flags); | |
57 | } | |
58 | ||
59 | static u32 mdscr_read(void) | |
60 | { | |
61 | u32 mdscr; | |
62 | asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr)); | |
63 | return mdscr; | |
64 | } | |
65 | ||
66 | /* | |
67 | * Allow root to disable self-hosted debug from userspace. | |
68 | * This is useful if you want to connect an external JTAG debugger. | |
69 | */ | |
70 | static u32 debug_enabled = 1; | |
71 | ||
72 | static int create_debug_debugfs_entry(void) | |
73 | { | |
74 | debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled); | |
75 | return 0; | |
76 | } | |
77 | fs_initcall(create_debug_debugfs_entry); | |
78 | ||
79 | static int __init early_debug_disable(char *buf) | |
80 | { | |
81 | debug_enabled = 0; | |
82 | return 0; | |
83 | } | |
84 | ||
85 | early_param("nodebugmon", early_debug_disable); | |
86 | ||
87 | /* | |
88 | * Keep track of debug users on each core. | |
89 | * The ref counts are per-cpu so we use a local_t type. | |
90 | */ | |
91 | static DEFINE_PER_CPU(local_t, mde_ref_count); | |
92 | static DEFINE_PER_CPU(local_t, kde_ref_count); | |
93 | ||
94 | void enable_debug_monitors(enum debug_el el) | |
95 | { | |
96 | u32 mdscr, enable = 0; | |
97 | ||
98 | WARN_ON(preemptible()); | |
99 | ||
100 | if (local_inc_return(&__get_cpu_var(mde_ref_count)) == 1) | |
101 | enable = DBG_MDSCR_MDE; | |
102 | ||
103 | if (el == DBG_ACTIVE_EL1 && | |
104 | local_inc_return(&__get_cpu_var(kde_ref_count)) == 1) | |
105 | enable |= DBG_MDSCR_KDE; | |
106 | ||
107 | if (enable && debug_enabled) { | |
108 | mdscr = mdscr_read(); | |
109 | mdscr |= enable; | |
110 | mdscr_write(mdscr); | |
111 | } | |
112 | } | |
113 | ||
114 | void disable_debug_monitors(enum debug_el el) | |
115 | { | |
116 | u32 mdscr, disable = 0; | |
117 | ||
118 | WARN_ON(preemptible()); | |
119 | ||
120 | if (local_dec_and_test(&__get_cpu_var(mde_ref_count))) | |
121 | disable = ~DBG_MDSCR_MDE; | |
122 | ||
123 | if (el == DBG_ACTIVE_EL1 && | |
124 | local_dec_and_test(&__get_cpu_var(kde_ref_count))) | |
125 | disable &= ~DBG_MDSCR_KDE; | |
126 | ||
127 | if (disable) { | |
128 | mdscr = mdscr_read(); | |
129 | mdscr &= disable; | |
130 | mdscr_write(mdscr); | |
131 | } | |
132 | } | |
133 | ||
134 | /* | |
135 | * OS lock clearing. | |
136 | */ | |
137 | static void clear_os_lock(void *unused) | |
138 | { | |
139 | asm volatile("msr mdscr_el1, %0" : : "r" (0)); | |
140 | isb(); | |
141 | asm volatile("msr oslar_el1, %0" : : "r" (0)); | |
142 | isb(); | |
143 | } | |
144 | ||
145 | static int __cpuinit os_lock_notify(struct notifier_block *self, | |
146 | unsigned long action, void *data) | |
147 | { | |
148 | int cpu = (unsigned long)data; | |
149 | if (action == CPU_ONLINE) | |
150 | smp_call_function_single(cpu, clear_os_lock, NULL, 1); | |
151 | return NOTIFY_OK; | |
152 | } | |
153 | ||
154 | static struct notifier_block __cpuinitdata os_lock_nb = { | |
155 | .notifier_call = os_lock_notify, | |
156 | }; | |
157 | ||
158 | static int __cpuinit debug_monitors_init(void) | |
159 | { | |
160 | /* Clear the OS lock. */ | |
161 | smp_call_function(clear_os_lock, NULL, 1); | |
162 | clear_os_lock(NULL); | |
163 | ||
164 | /* Register hotplug handler. */ | |
165 | register_cpu_notifier(&os_lock_nb); | |
166 | return 0; | |
167 | } | |
168 | postcore_initcall(debug_monitors_init); | |
169 | ||
170 | /* | |
171 | * Single step API and exception handling. | |
172 | */ | |
173 | static void set_regs_spsr_ss(struct pt_regs *regs) | |
174 | { | |
175 | unsigned long spsr; | |
176 | ||
177 | spsr = regs->pstate; | |
178 | spsr &= ~DBG_SPSR_SS; | |
179 | spsr |= DBG_SPSR_SS; | |
180 | regs->pstate = spsr; | |
181 | } | |
182 | ||
183 | static void clear_regs_spsr_ss(struct pt_regs *regs) | |
184 | { | |
185 | unsigned long spsr; | |
186 | ||
187 | spsr = regs->pstate; | |
188 | spsr &= ~DBG_SPSR_SS; | |
189 | regs->pstate = spsr; | |
190 | } | |
191 | ||
192 | static int single_step_handler(unsigned long addr, unsigned int esr, | |
193 | struct pt_regs *regs) | |
194 | { | |
195 | siginfo_t info; | |
196 | ||
197 | /* | |
198 | * If we are stepping a pending breakpoint, call the hw_breakpoint | |
199 | * handler first. | |
200 | */ | |
201 | if (!reinstall_suspended_bps(regs)) | |
202 | return 0; | |
203 | ||
204 | if (user_mode(regs)) { | |
205 | info.si_signo = SIGTRAP; | |
206 | info.si_errno = 0; | |
207 | info.si_code = TRAP_HWBKPT; | |
208 | info.si_addr = (void __user *)instruction_pointer(regs); | |
209 | force_sig_info(SIGTRAP, &info, current); | |
210 | ||
211 | /* | |
212 | * ptrace will disable single step unless explicitly | |
213 | * asked to re-enable it. For other clients, it makes | |
214 | * sense to leave it enabled (i.e. rewind the controls | |
215 | * to the active-not-pending state). | |
216 | */ | |
217 | user_rewind_single_step(current); | |
218 | } else { | |
219 | /* TODO: route to KGDB */ | |
220 | pr_warning("Unexpected kernel single-step exception at EL1\n"); | |
221 | /* | |
222 | * Re-enable stepping since we know that we will be | |
223 | * returning to regs. | |
224 | */ | |
225 | set_regs_spsr_ss(regs); | |
226 | } | |
227 | ||
228 | return 0; | |
229 | } | |
230 | ||
231 | static int __init single_step_init(void) | |
232 | { | |
233 | hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP, | |
234 | TRAP_HWBKPT, "single-step handler"); | |
235 | return 0; | |
236 | } | |
237 | arch_initcall(single_step_init); | |
238 | ||
239 | /* Re-enable single step for syscall restarting. */ | |
240 | void user_rewind_single_step(struct task_struct *task) | |
241 | { | |
242 | /* | |
243 | * If single step is active for this thread, then set SPSR.SS | |
244 | * to 1 to avoid returning to the active-pending state. | |
245 | */ | |
246 | if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) | |
247 | set_regs_spsr_ss(task_pt_regs(task)); | |
248 | } | |
249 | ||
250 | void user_fastforward_single_step(struct task_struct *task) | |
251 | { | |
252 | if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP)) | |
253 | clear_regs_spsr_ss(task_pt_regs(task)); | |
254 | } | |
255 | ||
256 | /* Kernel API */ | |
257 | void kernel_enable_single_step(struct pt_regs *regs) | |
258 | { | |
259 | WARN_ON(!irqs_disabled()); | |
260 | set_regs_spsr_ss(regs); | |
261 | mdscr_write(mdscr_read() | DBG_MDSCR_SS); | |
262 | enable_debug_monitors(DBG_ACTIVE_EL1); | |
263 | } | |
264 | ||
265 | void kernel_disable_single_step(void) | |
266 | { | |
267 | WARN_ON(!irqs_disabled()); | |
268 | mdscr_write(mdscr_read() & ~DBG_MDSCR_SS); | |
269 | disable_debug_monitors(DBG_ACTIVE_EL1); | |
270 | } | |
271 | ||
272 | int kernel_active_single_step(void) | |
273 | { | |
274 | WARN_ON(!irqs_disabled()); | |
275 | return mdscr_read() & DBG_MDSCR_SS; | |
276 | } | |
277 | ||
278 | /* ptrace API */ | |
279 | void user_enable_single_step(struct task_struct *task) | |
280 | { | |
281 | set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); | |
282 | set_regs_spsr_ss(task_pt_regs(task)); | |
283 | } | |
284 | ||
285 | void user_disable_single_step(struct task_struct *task) | |
286 | { | |
287 | clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); | |
288 | } |