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/signal.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 every time 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 */ 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 */ 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 } 127 128 void fpsimd_thread_switch(struct task_struct *next) 129 { 130 if (!system_supports_fpsimd()) 131 return; 132 /* 133 * Save the current FPSIMD state to memory, but only if whatever is in 134 * the registers is in fact the most recent userland FPSIMD state of 135 * 'current'. 136 */ 137 if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE)) 138 fpsimd_save_state(¤t->thread.fpsimd_state); 139 140 if (next->mm) { 141 /* 142 * If we are switching to a task whose most recent userland 143 * FPSIMD state is already in the registers of *this* cpu, 144 * we can skip loading the state from memory. Otherwise, set 145 * the TIF_FOREIGN_FPSTATE flag so the state will be loaded 146 * upon the next return to userland. 147 */ 148 struct fpsimd_state *st = &next->thread.fpsimd_state; 149 150 if (__this_cpu_read(fpsimd_last_state) == st 151 && st->cpu == smp_processor_id()) 152 clear_ti_thread_flag(task_thread_info(next), 153 TIF_FOREIGN_FPSTATE); 154 else 155 set_ti_thread_flag(task_thread_info(next), 156 TIF_FOREIGN_FPSTATE); 157 } 158 } 159 160 void fpsimd_flush_thread(void) 161 { 162 if (!system_supports_fpsimd()) 163 return; 164 memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state)); 165 fpsimd_flush_task_state(current); 166 set_thread_flag(TIF_FOREIGN_FPSTATE); 167 } 168 169 /* 170 * Save the userland FPSIMD state of 'current' to memory, but only if the state 171 * currently held in the registers does in fact belong to 'current' 172 */ 173 void fpsimd_preserve_current_state(void) 174 { 175 if (!system_supports_fpsimd()) 176 return; 177 preempt_disable(); 178 if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) 179 fpsimd_save_state(¤t->thread.fpsimd_state); 180 preempt_enable(); 181 } 182 183 /* 184 * Load the userland FPSIMD state of 'current' from memory, but only if the 185 * FPSIMD state already held in the registers is /not/ the most recent FPSIMD 186 * state of 'current' 187 */ 188 void fpsimd_restore_current_state(void) 189 { 190 if (!system_supports_fpsimd()) 191 return; 192 preempt_disable(); 193 if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) { 194 struct fpsimd_state *st = ¤t->thread.fpsimd_state; 195 196 fpsimd_load_state(st); 197 this_cpu_write(fpsimd_last_state, st); 198 st->cpu = smp_processor_id(); 199 } 200 preempt_enable(); 201 } 202 203 /* 204 * Load an updated userland FPSIMD state for 'current' from memory and set the 205 * flag that indicates that the FPSIMD register contents are the most recent 206 * FPSIMD state of 'current' 207 */ 208 void fpsimd_update_current_state(struct fpsimd_state *state) 209 { 210 if (!system_supports_fpsimd()) 211 return; 212 preempt_disable(); 213 fpsimd_load_state(state); 214 if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) { 215 struct fpsimd_state *st = ¤t->thread.fpsimd_state; 216 217 this_cpu_write(fpsimd_last_state, st); 218 st->cpu = smp_processor_id(); 219 } 220 preempt_enable(); 221 } 222 223 /* 224 * Invalidate live CPU copies of task t's FPSIMD state 225 */ 226 void fpsimd_flush_task_state(struct task_struct *t) 227 { 228 t->thread.fpsimd_state.cpu = NR_CPUS; 229 } 230 231 #ifdef CONFIG_KERNEL_MODE_NEON 232 233 static DEFINE_PER_CPU(struct fpsimd_partial_state, hardirq_fpsimdstate); 234 static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate); 235 236 /* 237 * Kernel-side NEON support functions 238 */ 239 void kernel_neon_begin_partial(u32 num_regs) 240 { 241 if (WARN_ON(!system_supports_fpsimd())) 242 return; 243 if (in_interrupt()) { 244 struct fpsimd_partial_state *s = this_cpu_ptr( 245 in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate); 246 247 BUG_ON(num_regs > 32); 248 fpsimd_save_partial_state(s, roundup(num_regs, 2)); 249 } else { 250 /* 251 * Save the userland FPSIMD state if we have one and if we 252 * haven't done so already. Clear fpsimd_last_state to indicate 253 * that there is no longer userland FPSIMD state in the 254 * registers. 255 */ 256 preempt_disable(); 257 if (current->mm && 258 !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE)) 259 fpsimd_save_state(¤t->thread.fpsimd_state); 260 this_cpu_write(fpsimd_last_state, NULL); 261 } 262 } 263 EXPORT_SYMBOL(kernel_neon_begin_partial); 264 265 void kernel_neon_end(void) 266 { 267 if (!system_supports_fpsimd()) 268 return; 269 if (in_interrupt()) { 270 struct fpsimd_partial_state *s = this_cpu_ptr( 271 in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate); 272 fpsimd_load_partial_state(s); 273 } else { 274 preempt_enable(); 275 } 276 } 277 EXPORT_SYMBOL(kernel_neon_end); 278 279 #endif /* CONFIG_KERNEL_MODE_NEON */ 280 281 #ifdef CONFIG_CPU_PM 282 static int fpsimd_cpu_pm_notifier(struct notifier_block *self, 283 unsigned long cmd, void *v) 284 { 285 switch (cmd) { 286 case CPU_PM_ENTER: 287 if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE)) 288 fpsimd_save_state(¤t->thread.fpsimd_state); 289 this_cpu_write(fpsimd_last_state, NULL); 290 break; 291 case CPU_PM_EXIT: 292 if (current->mm) 293 set_thread_flag(TIF_FOREIGN_FPSTATE); 294 break; 295 case CPU_PM_ENTER_FAILED: 296 default: 297 return NOTIFY_DONE; 298 } 299 return NOTIFY_OK; 300 } 301 302 static struct notifier_block fpsimd_cpu_pm_notifier_block = { 303 .notifier_call = fpsimd_cpu_pm_notifier, 304 }; 305 306 static void __init fpsimd_pm_init(void) 307 { 308 cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block); 309 } 310 311 #else 312 static inline void fpsimd_pm_init(void) { } 313 #endif /* CONFIG_CPU_PM */ 314 315 #ifdef CONFIG_HOTPLUG_CPU 316 static int fpsimd_cpu_dead(unsigned int cpu) 317 { 318 per_cpu(fpsimd_last_state, cpu) = NULL; 319 return 0; 320 } 321 322 static inline void fpsimd_hotplug_init(void) 323 { 324 cpuhp_setup_state_nocalls(CPUHP_ARM64_FPSIMD_DEAD, "arm64/fpsimd:dead", 325 NULL, fpsimd_cpu_dead); 326 } 327 328 #else 329 static inline void fpsimd_hotplug_init(void) { } 330 #endif 331 332 /* 333 * FP/SIMD support code initialisation. 334 */ 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