1 /*
2 * FP/SIMD context switching and fault handling
3 *
4 * Copyright (C) 2012 ARM Ltd.
5 * Author: Catalin Marinas <catalin.marinas@arm.com>
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 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
18 */
19
20 #include <linux/cpu.h>
21 #include <linux/cpu_pm.h>
22 #include <linux/kernel.h>
23 #include <linux/init.h>
24 #include <linux/sched.h>
25 #include <linux/signal.h>
26 #include <linux/hardirq.h>
27
28 #include <asm/fpsimd.h>
29 #include <asm/cputype.h>
30
31 #define FPEXC_IOF (1 << 0)
32 #define FPEXC_DZF (1 << 1)
33 #define FPEXC_OFF (1 << 2)
34 #define FPEXC_UFF (1 << 3)
35 #define FPEXC_IXF (1 << 4)
36 #define FPEXC_IDF (1 << 7)
37
38 /*
39 * In order to reduce the number of times the FPSIMD state is needlessly saved
40 * and restored, we need to keep track of two things:
41 * (a) for each task, we need to remember which CPU was the last one to have
42 * the task's FPSIMD state loaded into its FPSIMD registers;
43 * (b) for each CPU, we need to remember which task's userland FPSIMD state has
44 * been loaded into its FPSIMD registers most recently, or whether it has
45 * been used to perform kernel mode NEON in the meantime.
46 *
47 * For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to
48 * the id of the current CPU everytime the state is loaded onto a CPU. For (b),
49 * we add the per-cpu variable 'fpsimd_last_state' (below), which contains the
50 * address of the userland FPSIMD state of the task that was loaded onto the CPU
51 * the most recently, or NULL if kernel mode NEON has been performed after that.
52 *
53 * With this in place, we no longer have to restore the next FPSIMD state right
54 * when switching between tasks. Instead, we can defer this check to userland
55 * resume, at which time we verify whether the CPU's fpsimd_last_state and the
56 * task's fpsimd_state.cpu are still mutually in sync. If this is the case, we
57 * can omit the FPSIMD restore.
58 *
59 * As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to
60 * indicate whether or not the userland FPSIMD state of the current task is
61 * present in the registers. The flag is set unless the FPSIMD registers of this
62 * CPU currently contain the most recent userland FPSIMD state of the current
63 * task.
64 *
65 * For a certain task, the sequence may look something like this:
66 * - the task gets scheduled in; if both the task's fpsimd_state.cpu field
67 * contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu
68 * variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is
69 * cleared, otherwise it is set;
70 *
71 * - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's
72 * userland FPSIMD state is copied from memory to the registers, the task's
73 * fpsimd_state.cpu field is set to the id of the current CPU, the current
74 * CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the
75 * TIF_FOREIGN_FPSTATE flag is cleared;
76 *
77 * - the task executes an ordinary syscall; upon return to userland, the
78 * TIF_FOREIGN_FPSTATE flag will still be cleared, so no FPSIMD state is
79 * restored;
80 *
81 * - the task executes a syscall which executes some NEON instructions; this is
82 * preceded by a call to kernel_neon_begin(), which copies the task's FPSIMD
83 * register contents to memory, clears the fpsimd_last_state per-cpu variable
84 * and sets the TIF_FOREIGN_FPSTATE flag;
85 *
86 * - the task gets preempted after kernel_neon_end() is called; as we have not
87 * returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so
88 * whatever is in the FPSIMD registers is not saved to memory, but discarded.
89 */
90 static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);
91
92 /*
93 * Trapped FP/ASIMD access.
94 */
do_fpsimd_acc(unsigned int esr,struct pt_regs * regs)95 void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
96 {
97 /* TODO: implement lazy context saving/restoring */
98 WARN_ON(1);
99 }
100
101 /*
102 * Raise a SIGFPE for the current process.
103 */
do_fpsimd_exc(unsigned int esr,struct pt_regs * regs)104 void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
105 {
106 siginfo_t info;
107 unsigned int si_code = 0;
108
109 if (esr & FPEXC_IOF)
110 si_code = FPE_FLTINV;
111 else if (esr & FPEXC_DZF)
112 si_code = FPE_FLTDIV;
113 else if (esr & FPEXC_OFF)
114 si_code = FPE_FLTOVF;
115 else if (esr & FPEXC_UFF)
116 si_code = FPE_FLTUND;
117 else if (esr & FPEXC_IXF)
118 si_code = FPE_FLTRES;
119
120 memset(&info, 0, sizeof(info));
121 info.si_signo = SIGFPE;
122 info.si_code = si_code;
123 info.si_addr = (void __user *)instruction_pointer(regs);
124
125 send_sig_info(SIGFPE, &info, current);
126 }
127
fpsimd_thread_switch(struct task_struct * next)128 void fpsimd_thread_switch(struct task_struct *next)
129 {
130 /*
131 * Save the current FPSIMD state to memory, but only if whatever is in
132 * the registers is in fact the most recent userland FPSIMD state of
133 * 'current'.
134 */
135 if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
136 fpsimd_save_state(¤t->thread.fpsimd_state);
137
138 if (next->mm) {
139 /*
140 * If we are switching to a task whose most recent userland
141 * FPSIMD state is already in the registers of *this* cpu,
142 * we can skip loading the state from memory. Otherwise, set
143 * the TIF_FOREIGN_FPSTATE flag so the state will be loaded
144 * upon the next return to userland.
145 */
146 struct fpsimd_state *st = &next->thread.fpsimd_state;
147
148 if (__this_cpu_read(fpsimd_last_state) == st
149 && st->cpu == smp_processor_id())
150 clear_ti_thread_flag(task_thread_info(next),
151 TIF_FOREIGN_FPSTATE);
152 else
153 set_ti_thread_flag(task_thread_info(next),
154 TIF_FOREIGN_FPSTATE);
155 }
156 }
157
fpsimd_flush_thread(void)158 void fpsimd_flush_thread(void)
159 {
160 preempt_disable();
161 memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
162 fpsimd_flush_task_state(current);
163 set_thread_flag(TIF_FOREIGN_FPSTATE);
164 preempt_enable();
165 }
166
167 /*
168 * Save the userland FPSIMD state of 'current' to memory, but only if the state
169 * currently held in the registers does in fact belong to 'current'
170 */
fpsimd_preserve_current_state(void)171 void fpsimd_preserve_current_state(void)
172 {
173 preempt_disable();
174 if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
175 fpsimd_save_state(¤t->thread.fpsimd_state);
176 preempt_enable();
177 }
178
179 /*
180 * Load the userland FPSIMD state of 'current' from memory, but only if the
181 * FPSIMD state already held in the registers is /not/ the most recent FPSIMD
182 * state of 'current'
183 */
fpsimd_restore_current_state(void)184 void fpsimd_restore_current_state(void)
185 {
186 preempt_disable();
187 if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
188 struct fpsimd_state *st = ¤t->thread.fpsimd_state;
189
190 fpsimd_load_state(st);
191 this_cpu_write(fpsimd_last_state, st);
192 st->cpu = smp_processor_id();
193 }
194 preempt_enable();
195 }
196
197 /*
198 * Load an updated userland FPSIMD state for 'current' from memory and set the
199 * flag that indicates that the FPSIMD register contents are the most recent
200 * FPSIMD state of 'current'
201 */
fpsimd_update_current_state(struct fpsimd_state * state)202 void fpsimd_update_current_state(struct fpsimd_state *state)
203 {
204 preempt_disable();
205 fpsimd_load_state(state);
206 if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
207 struct fpsimd_state *st = ¤t->thread.fpsimd_state;
208
209 this_cpu_write(fpsimd_last_state, st);
210 st->cpu = smp_processor_id();
211 }
212 preempt_enable();
213 }
214
215 /*
216 * Invalidate live CPU copies of task t's FPSIMD state
217 */
fpsimd_flush_task_state(struct task_struct * t)218 void fpsimd_flush_task_state(struct task_struct *t)
219 {
220 t->thread.fpsimd_state.cpu = NR_CPUS;
221 }
222
223 #ifdef CONFIG_KERNEL_MODE_NEON
224
225 static DEFINE_PER_CPU(struct fpsimd_partial_state, hardirq_fpsimdstate);
226 static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate);
227
228 /*
229 * Kernel-side NEON support functions
230 */
kernel_neon_begin_partial(u32 num_regs)231 void kernel_neon_begin_partial(u32 num_regs)
232 {
233 if (in_interrupt()) {
234 struct fpsimd_partial_state *s = this_cpu_ptr(
235 in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
236
237 BUG_ON(num_regs > 32);
238 fpsimd_save_partial_state(s, roundup(num_regs, 2));
239 } else {
240 /*
241 * Save the userland FPSIMD state if we have one and if we
242 * haven't done so already. Clear fpsimd_last_state to indicate
243 * that there is no longer userland FPSIMD state in the
244 * registers.
245 */
246 preempt_disable();
247 if (current->mm &&
248 !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
249 fpsimd_save_state(¤t->thread.fpsimd_state);
250 this_cpu_write(fpsimd_last_state, NULL);
251 }
252 }
253 EXPORT_SYMBOL(kernel_neon_begin_partial);
254
kernel_neon_end(void)255 void kernel_neon_end(void)
256 {
257 if (in_interrupt()) {
258 struct fpsimd_partial_state *s = this_cpu_ptr(
259 in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
260 fpsimd_load_partial_state(s);
261 } else {
262 preempt_enable();
263 }
264 }
265 EXPORT_SYMBOL(kernel_neon_end);
266
267 #endif /* CONFIG_KERNEL_MODE_NEON */
268
269 #ifdef CONFIG_CPU_PM
fpsimd_cpu_pm_notifier(struct notifier_block * self,unsigned long cmd,void * v)270 static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
271 unsigned long cmd, void *v)
272 {
273 switch (cmd) {
274 case CPU_PM_ENTER:
275 if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
276 fpsimd_save_state(¤t->thread.fpsimd_state);
277 this_cpu_write(fpsimd_last_state, NULL);
278 break;
279 case CPU_PM_EXIT:
280 if (current->mm)
281 set_thread_flag(TIF_FOREIGN_FPSTATE);
282 break;
283 case CPU_PM_ENTER_FAILED:
284 default:
285 return NOTIFY_DONE;
286 }
287 return NOTIFY_OK;
288 }
289
290 static struct notifier_block fpsimd_cpu_pm_notifier_block = {
291 .notifier_call = fpsimd_cpu_pm_notifier,
292 };
293
fpsimd_pm_init(void)294 static void __init fpsimd_pm_init(void)
295 {
296 cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block);
297 }
298
299 #else
fpsimd_pm_init(void)300 static inline void fpsimd_pm_init(void) { }
301 #endif /* CONFIG_CPU_PM */
302
303 #ifdef CONFIG_HOTPLUG_CPU
fpsimd_cpu_hotplug_notifier(struct notifier_block * nfb,unsigned long action,void * hcpu)304 static int fpsimd_cpu_hotplug_notifier(struct notifier_block *nfb,
305 unsigned long action,
306 void *hcpu)
307 {
308 unsigned int cpu = (long)hcpu;
309
310 switch (action) {
311 case CPU_DEAD:
312 case CPU_DEAD_FROZEN:
313 per_cpu(fpsimd_last_state, cpu) = NULL;
314 break;
315 }
316 return NOTIFY_OK;
317 }
318
319 static struct notifier_block fpsimd_cpu_hotplug_notifier_block = {
320 .notifier_call = fpsimd_cpu_hotplug_notifier,
321 };
322
fpsimd_hotplug_init(void)323 static inline void fpsimd_hotplug_init(void)
324 {
325 register_cpu_notifier(&fpsimd_cpu_hotplug_notifier_block);
326 }
327
328 #else
fpsimd_hotplug_init(void)329 static inline void fpsimd_hotplug_init(void) { }
330 #endif
331
332 /*
333 * FP/SIMD support code initialisation.
334 */
fpsimd_init(void)335 static int __init fpsimd_init(void)
336 {
337 if (elf_hwcap & HWCAP_FP) {
338 fpsimd_pm_init();
339 fpsimd_hotplug_init();
340 } else {
341 pr_notice("Floating-point is not implemented\n");
342 }
343
344 if (!(elf_hwcap & HWCAP_ASIMD))
345 pr_notice("Advanced SIMD is not implemented\n");
346
347 return 0;
348 }
349 late_initcall(fpsimd_init);
350