arch/arm64/kernel/fpsimd.c

   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(&current->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(&current->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(&current->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 = &current->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 = &current->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(&current->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(&current->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_hotplug_notifier(struct notifier_block *nfb,
 303                                        unsigned long action,
 304                                        void *hcpu)
 305 {
 306         unsigned int cpu = (long)hcpu;
 307
 308         switch (action) {
 309         case CPU_DEAD:
 310         case CPU_DEAD_FROZEN:
 311                 per_cpu(fpsimd_last_state, cpu) = NULL;
 312                 break;
 313         }
 314         return NOTIFY_OK;
 315 }
 316
 317 static struct notifier_block fpsimd_cpu_hotplug_notifier_block = {
 318         .notifier_call = fpsimd_cpu_hotplug_notifier,
 319 };
 320
 321 static inline void fpsimd_hotplug_init(void)
 322 {
 323         register_cpu_notifier(&fpsimd_cpu_hotplug_notifier_block);
 324 }
 325
 326 #else
 327 static inline void fpsimd_hotplug_init(void) { }
 328 #endif
 329
 330 /*
 331  * FP/SIMD support code initialisation.
 332  */
 333 static int __init fpsimd_init(void)
 334 {
 335         if (elf_hwcap & HWCAP_FP) {
 336                 fpsimd_pm_init();
 337                 fpsimd_hotplug_init();
 338         } else {
 339                 pr_notice("Floating-point is not implemented\n");
 340         }
 341
 342         if (!(elf_hwcap & HWCAP_ASIMD))
 343                 pr_notice("Advanced SIMD is not implemented\n");
 344
 345         return 0;
 346 }
 347 late_initcall(fpsimd_init);