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 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 /* 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 } 157 158 void fpsimd_flush_thread(void) 159 { 160 memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state)); 161 fpsimd_flush_task_state(current); 162 set_thread_flag(TIF_FOREIGN_FPSTATE); 163 } 164 165 /* 166 * Save the userland FPSIMD state of 'current' to memory, but only if the state 167 * currently held in the registers does in fact belong to 'current' 168 */ 169 void fpsimd_preserve_current_state(void) 170 { 171 preempt_disable(); 172 if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) 173 fpsimd_save_state(¤t->thread.fpsimd_state); 174 preempt_enable(); 175 } 176 177 /* 178 * Load the userland FPSIMD state of 'current' from memory, but only if the 179 * FPSIMD state already held in the registers is /not/ the most recent FPSIMD 180 * state of 'current' 181 */ 182 void fpsimd_restore_current_state(void) 183 { 184 preempt_disable(); 185 if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) { 186 struct fpsimd_state *st = ¤t->thread.fpsimd_state; 187 188 fpsimd_load_state(st); 189 this_cpu_write(fpsimd_last_state, st); 190 st->cpu = smp_processor_id(); 191 } 192 preempt_enable(); 193 } 194 195 /* 196 * Load an updated userland FPSIMD state for 'current' from memory and set the 197 * flag that indicates that the FPSIMD register contents are the most recent 198 * FPSIMD state of 'current' 199 */ 200 void fpsimd_update_current_state(struct fpsimd_state *state) 201 { 202 preempt_disable(); 203 fpsimd_load_state(state); 204 if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) { 205 struct fpsimd_state *st = ¤t->thread.fpsimd_state; 206 207 this_cpu_write(fpsimd_last_state, st); 208 st->cpu = smp_processor_id(); 209 } 210 preempt_enable(); 211 } 212 213 /* 214 * Invalidate live CPU copies of task t's FPSIMD state 215 */ 216 void fpsimd_flush_task_state(struct task_struct *t) 217 { 218 t->thread.fpsimd_state.cpu = NR_CPUS; 219 } 220 221 #ifdef CONFIG_KERNEL_MODE_NEON 222 223 static DEFINE_PER_CPU(struct fpsimd_partial_state, hardirq_fpsimdstate); 224 static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate); 225 226 /* 227 * Kernel-side NEON support functions 228 */ 229 void kernel_neon_begin_partial(u32 num_regs) 230 { 231 if (in_interrupt()) { 232 struct fpsimd_partial_state *s = this_cpu_ptr( 233 in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate); 234 235 BUG_ON(num_regs > 32); 236 fpsimd_save_partial_state(s, roundup(num_regs, 2)); 237 } else { 238 /* 239 * Save the userland FPSIMD state if we have one and if we 240 * haven't done so already. Clear fpsimd_last_state to indicate 241 * that there is no longer userland FPSIMD state in the 242 * registers. 243 */ 244 preempt_disable(); 245 if (current->mm && 246 !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE)) 247 fpsimd_save_state(¤t->thread.fpsimd_state); 248 this_cpu_write(fpsimd_last_state, NULL); 249 } 250 } 251 EXPORT_SYMBOL(kernel_neon_begin_partial); 252 253 void kernel_neon_end(void) 254 { 255 if (in_interrupt()) { 256 struct fpsimd_partial_state *s = this_cpu_ptr( 257 in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate); 258 fpsimd_load_partial_state(s); 259 } else { 260 preempt_enable(); 261 } 262 } 263 EXPORT_SYMBOL(kernel_neon_end); 264 265 #endif /* CONFIG_KERNEL_MODE_NEON */ 266 267 #ifdef CONFIG_CPU_PM 268 static int fpsimd_cpu_pm_notifier(struct notifier_block *self, 269 unsigned long cmd, void *v) 270 { 271 switch (cmd) { 272 case CPU_PM_ENTER: 273 if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE)) 274 fpsimd_save_state(¤t->thread.fpsimd_state); 275 this_cpu_write(fpsimd_last_state, NULL); 276 break; 277 case CPU_PM_EXIT: 278 if (current->mm) 279 set_thread_flag(TIF_FOREIGN_FPSTATE); 280 break; 281 case CPU_PM_ENTER_FAILED: 282 default: 283 return NOTIFY_DONE; 284 } 285 return NOTIFY_OK; 286 } 287 288 static struct notifier_block fpsimd_cpu_pm_notifier_block = { 289 .notifier_call = fpsimd_cpu_pm_notifier, 290 }; 291 292 static void __init fpsimd_pm_init(void) 293 { 294 cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block); 295 } 296 297 #else 298 static inline void fpsimd_pm_init(void) { } 299 #endif /* CONFIG_CPU_PM */ 300 301 #ifdef CONFIG_HOTPLUG_CPU 302 static int fpsimd_cpu_dead(unsigned int cpu) 303 { 304 per_cpu(fpsimd_last_state, cpu) = NULL; 305 return 0; 306 } 307 308 static inline void fpsimd_hotplug_init(void) 309 { 310 cpuhp_setup_state_nocalls(CPUHP_ARM64_FPSIMD_DEAD, "arm64/fpsimd:dead", 311 NULL, fpsimd_cpu_dead); 312 } 313 314 #else 315 static inline void fpsimd_hotplug_init(void) { } 316 #endif 317 318 /* 319 * FP/SIMD support code initialisation. 320 */ 321 static int __init fpsimd_init(void) 322 { 323 if (elf_hwcap & HWCAP_FP) { 324 fpsimd_pm_init(); 325 fpsimd_hotplug_init(); 326 } else { 327 pr_notice("Floating-point is not implemented\n"); 328 } 329 330 if (!(elf_hwcap & HWCAP_ASIMD)) 331 pr_notice("Advanced SIMD is not implemented\n"); 332 333 return 0; 334 } 335 late_initcall(fpsimd_init); 336