arch/mips/kernel/process.c

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Copyright (C) 1994 - 1999, 2000 by Ralf Baechle and others.
   7  * Copyright (C) 2005, 2006 by Ralf Baechle (ralf@linux-mips.org)
   8  * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
   9  * Copyright (C) 2004 Thiemo Seufer
  10  * Copyright (C) 2013  Imagination Technologies Ltd.
  11  */
  12 #include <linux/errno.h>
  13 #include <linux/sched.h>
  14 #include <linux/tick.h>
  15 #include <linux/kernel.h>
  16 #include <linux/mm.h>
  17 #include <linux/stddef.h>
  18 #include <linux/unistd.h>
  19 #include <linux/export.h>
  20 #include <linux/ptrace.h>
  21 #include <linux/mman.h>
  22 #include <linux/personality.h>
  23 #include <linux/sys.h>
  24 #include <linux/init.h>
  25 #include <linux/completion.h>
  26 #include <linux/kallsyms.h>
  27 #include <linux/random.h>
  28 #include <linux/prctl.h>
  29
  30 #include <asm/asm.h>
  31 #include <asm/bootinfo.h>
  32 #include <asm/cpu.h>
  33 #include <asm/dsp.h>
  34 #include <asm/fpu.h>
  35 #include <asm/msa.h>
  36 #include <asm/pgtable.h>
  37 #include <asm/mipsregs.h>
  38 #include <asm/processor.h>
  39 #include <asm/reg.h>
  40 #include <asm/uaccess.h>
  41 #include <asm/io.h>
  42 #include <asm/elf.h>
  43 #include <asm/isadep.h>
  44 #include <asm/inst.h>
  45 #include <asm/stacktrace.h>
  46 #include <asm/irq_regs.h>
  47
  48 #ifdef CONFIG_HOTPLUG_CPU
  49 void arch_cpu_idle_dead(void)
  50 {
  51         /* What the heck is this check doing ? */
  52         if (!cpumask_test_cpu(smp_processor_id(), &cpu_callin_map))
  53                 play_dead();
  54 }
  55 #endif
  56
  57 asmlinkage void ret_from_fork(void);
  58 asmlinkage void ret_from_kernel_thread(void);
  59
  60 void start_thread(struct pt_regs * regs, unsigned long pc, unsigned long sp)
  61 {
  62         unsigned long status;
  63
  64         /* New thread loses kernel privileges. */
  65         status = regs->cp0_status & ~(ST0_CU0|ST0_CU1|ST0_FR|KU_MASK);
  66         status |= KU_USER;
  67         regs->cp0_status = status;
  68         clear_used_math();
  69         clear_fpu_owner();
  70         init_dsp();
  71         clear_thread_flag(TIF_USEDMSA);
  72         clear_thread_flag(TIF_MSA_CTX_LIVE);
  73         disable_msa();
  74         regs->cp0_epc = pc;
  75         regs->regs[29] = sp;
  76 }
  77
  78 void exit_thread(void)
  79 {
  80 }
  81
  82 void flush_thread(void)
  83 {
  84 }
  85
  86 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
  87 {
  88         /*
  89          * Save any process state which is live in hardware registers to the
  90          * parent context prior to duplication. This prevents the new child
  91          * state becoming stale if the parent is preempted before copy_thread()
  92          * gets a chance to save the parent's live hardware registers to the
  93          * child context.
  94          */
  95         preempt_disable();
  96
  97         if (is_msa_enabled())
  98                 save_msa(current);
  99         else if (is_fpu_owner())
 100                 _save_fp(current);
 101
 102         save_dsp(current);
 103
 104         preempt_enable();
 105
 106         *dst = *src;
 107         return 0;
 108 }
 109
 110 /*
 111  * Copy architecture-specific thread state
 112  */
 113 int copy_thread(unsigned long clone_flags, unsigned long usp,
 114         unsigned long kthread_arg, struct task_struct *p)
 115 {
 116         struct thread_info *ti = task_thread_info(p);
 117         struct pt_regs *childregs, *regs = current_pt_regs();
 118         unsigned long childksp;
 119         p->set_child_tid = p->clear_child_tid = NULL;
 120
 121         childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE - 32;
 122
 123         /* set up new TSS. */
 124         childregs = (struct pt_regs *) childksp - 1;
 125         /*  Put the stack after the struct pt_regs.  */
 126         childksp = (unsigned long) childregs;
 127         p->thread.cp0_status = read_c0_status() & ~(ST0_CU2|ST0_CU1);
 128         if (unlikely(p->flags & PF_KTHREAD)) {
 129                 /* kernel thread */
 130                 unsigned long status = p->thread.cp0_status;
 131                 memset(childregs, 0, sizeof(struct pt_regs));
 132                 ti->addr_limit = KERNEL_DS;
 133                 p->thread.reg16 = usp; /* fn */
 134                 p->thread.reg17 = kthread_arg;
 135                 p->thread.reg29 = childksp;
 136                 p->thread.reg31 = (unsigned long) ret_from_kernel_thread;
 137 #if defined(CONFIG_CPU_R3000) || defined(CONFIG_CPU_TX39XX)
 138                 status = (status & ~(ST0_KUP | ST0_IEP | ST0_IEC)) |
 139                          ((status & (ST0_KUC | ST0_IEC)) << 2);
 140 #else
 141                 status |= ST0_EXL;
 142 #endif
 143                 childregs->cp0_status = status;
 144                 return 0;
 145         }
 146
 147         /* user thread */
 148         *childregs = *regs;
 149         childregs->regs[7] = 0; /* Clear error flag */
 150         childregs->regs[2] = 0; /* Child gets zero as return value */
 151         if (usp)
 152                 childregs->regs[29] = usp;
 153         ti->addr_limit = USER_DS;
 154
 155         p->thread.reg29 = (unsigned long) childregs;
 156         p->thread.reg31 = (unsigned long) ret_from_fork;
 157
 158         /*
 159          * New tasks lose permission to use the fpu. This accelerates context
 160          * switching for most programs since they don't use the fpu.
 161          */
 162         childregs->cp0_status &= ~(ST0_CU2|ST0_CU1);
 163
 164         clear_tsk_thread_flag(p, TIF_USEDFPU);
 165         clear_tsk_thread_flag(p, TIF_USEDMSA);
 166         clear_tsk_thread_flag(p, TIF_MSA_CTX_LIVE);
 167
 168 #ifdef CONFIG_MIPS_MT_FPAFF
 169         clear_tsk_thread_flag(p, TIF_FPUBOUND);
 170 #endif /* CONFIG_MIPS_MT_FPAFF */
 171
 172         if (clone_flags & CLONE_SETTLS)
 173                 ti->tp_value = regs->regs[7];
 174
 175         return 0;
 176 }
 177
 178 #ifdef CONFIG_CC_STACKPROTECTOR
 179 #include <linux/stackprotector.h>
 180 unsigned long __stack_chk_guard __read_mostly;
 181 EXPORT_SYMBOL(__stack_chk_guard);
 182 #endif
 183
 184 struct mips_frame_info {
 185         void            *func;
 186         unsigned long   func_size;
 187         int             frame_size;
 188         int             pc_offset;
 189 };
 190
 191 #define J_TARGET(pc,target)     \
 192                 (((unsigned long)(pc) & 0xf0000000) | ((target) << 2))
 193
 194 static inline int is_ra_save_ins(union mips_instruction *ip)
 195 {
 196 #ifdef CONFIG_CPU_MICROMIPS
 197         /*
 198          * swsp ra,offset
 199          * swm16 reglist,offset(sp)
 200          * swm32 reglist,offset(sp)
 201          * sw32 ra,offset(sp)
 202          * jradiussp - NOT SUPPORTED
 203          *
 204          * microMIPS is way more fun...
 205          */
 206         if (mm_insn_16bit(ip->halfword[1])) {
 207                 return (ip->mm16_r5_format.opcode == mm_swsp16_op &&
 208                         ip->mm16_r5_format.rt == 31) ||
 209                        (ip->mm16_m_format.opcode == mm_pool16c_op &&
 210                         ip->mm16_m_format.func == mm_swm16_op);
 211         }
 212         else {
 213                 return (ip->mm_m_format.opcode == mm_pool32b_op &&
 214                         ip->mm_m_format.rd > 9 &&
 215                         ip->mm_m_format.base == 29 &&
 216                         ip->mm_m_format.func == mm_swm32_func) ||
 217                        (ip->i_format.opcode == mm_sw32_op &&
 218                         ip->i_format.rs == 29 &&
 219                         ip->i_format.rt == 31);
 220         }
 221 #else
 222         /* sw / sd $ra, offset($sp) */
 223         return (ip->i_format.opcode == sw_op || ip->i_format.opcode == sd_op) &&
 224                 ip->i_format.rs == 29 &&
 225                 ip->i_format.rt == 31;
 226 #endif
 227 }
 228
 229 static inline int is_jump_ins(union mips_instruction *ip)
 230 {
 231 #ifdef CONFIG_CPU_MICROMIPS
 232         /*
 233          * jr16,jrc,jalr16,jalr16
 234          * jal
 235          * jalr/jr,jalr.hb/jr.hb,jalrs,jalrs.hb
 236          * jraddiusp - NOT SUPPORTED
 237          *
 238          * microMIPS is kind of more fun...
 239          */
 240         if ((ip->mm16_r5_format.opcode == mm_pool16c_op &&
 241             (ip->mm16_r5_format.rt & mm_jr16_op) == mm_jr16_op) ||
 242             ip->j_format.opcode == mm_jal32_op)
 243                 return 1;
 244         if (ip->r_format.opcode != mm_pool32a_op ||
 245                         ip->r_format.func != mm_pool32axf_op)
 246                 return 0;
 247         return ((ip->u_format.uimmediate >> 6) & mm_jalr_op) == mm_jalr_op;
 248 #else
 249         if (ip->j_format.opcode == j_op)
 250                 return 1;
 251         if (ip->j_format.opcode == jal_op)
 252                 return 1;
 253         if (ip->r_format.opcode != spec_op)
 254                 return 0;
 255         return ip->r_format.func == jalr_op || ip->r_format.func == jr_op;
 256 #endif
 257 }
 258
 259 static inline int is_sp_move_ins(union mips_instruction *ip)
 260 {
 261 #ifdef CONFIG_CPU_MICROMIPS
 262         /*
 263          * addiusp -imm
 264          * addius5 sp,-imm
 265          * addiu32 sp,sp,-imm
 266          * jradiussp - NOT SUPPORTED
 267          *
 268          * microMIPS is not more fun...
 269          */
 270         if (mm_insn_16bit(ip->halfword[1])) {
 271                 return (ip->mm16_r3_format.opcode == mm_pool16d_op &&
 272                         ip->mm16_r3_format.simmediate && mm_addiusp_func) ||
 273                        (ip->mm16_r5_format.opcode == mm_pool16d_op &&
 274                         ip->mm16_r5_format.rt == 29);
 275         }
 276
 277         return ip->mm_i_format.opcode == mm_addiu32_op &&
 278                ip->mm_i_format.rt == 29 && ip->mm_i_format.rs == 29;
 279 #else
 280         /* addiu/daddiu sp,sp,-imm */
 281         if (ip->i_format.rs != 29 || ip->i_format.rt != 29)
 282                 return 0;
 283         if (ip->i_format.opcode == addiu_op || ip->i_format.opcode == daddiu_op)
 284                 return 1;
 285 #endif
 286         return 0;
 287 }
 288
 289 static int get_frame_info(struct mips_frame_info *info)
 290 {
 291         bool is_mmips = IS_ENABLED(CONFIG_CPU_MICROMIPS);
 292         union mips_instruction insn, *ip;
 293         unsigned max_insns = info->func_size / sizeof(union mips_instruction);
 294         unsigned i;
 295
 296         info->pc_offset = -1;
 297         info->frame_size = 0;
 298
 299         ip = (void *)msk_isa16_mode((ulong)info->func);
 300         if (!ip)
 301                 goto err;
 302
 303         if (max_insns == 0)
 304                 max_insns = 128U;       /* unknown function size */
 305         max_insns = min(128U, max_insns);
 306
 307         for (i = 0; i < max_insns; i++, ip++) {
 308                 if (is_mmips && mm_insn_16bit(ip->halfword[0])) {
 309                         insn.halfword[0] = 0;
 310                         insn.halfword[1] = ip->halfword[0];
 311                 } else if (is_mmips) {
 312                         insn.halfword[0] = ip->halfword[1];
 313                         insn.halfword[1] = ip->halfword[0];
 314                 } else {
 315                         insn.word = ip->word;
 316                 }
 317
 318                 if (is_jump_ins(&insn))
 319                         break;
 320
 321                 if (!info->frame_size) {
 322                         if (is_sp_move_ins(&insn))
 323                         {
 324 #ifdef CONFIG_CPU_MICROMIPS
 325                                 if (mm_insn_16bit(ip->halfword[0]))
 326                                 {
 327                                         unsigned short tmp;
 328
 329                                         if (ip->halfword[0] & mm_addiusp_func)
 330                                         {
 331                                                 tmp = (((ip->halfword[0] >> 1) & 0x1ff) << 2);
 332                                                 info->frame_size = -(signed short)(tmp | ((tmp & 0x100) ? 0xfe00 : 0));
 333                                         } else {
 334                                                 tmp = (ip->halfword[0] >> 1);
 335                                                 info->frame_size = -(signed short)(tmp & 0xf);
 336                                         }
 337                                         ip = (void *) &ip->halfword[1];
 338                                         ip--;
 339                                 } else
 340 #endif
 341                                 info->frame_size = - ip->i_format.simmediate;
 342                         }
 343                         continue;
 344                 }
 345                 if (info->pc_offset == -1 && is_ra_save_ins(&insn)) {
 346                         info->pc_offset =
 347                                 ip->i_format.simmediate / sizeof(long);
 348                         break;
 349                 }
 350         }
 351         if (info->frame_size && info->pc_offset >= 0) /* nested */
 352                 return 0;
 353         if (info->pc_offset < 0) /* leaf */
 354                 return 1;
 355         /* prologue seems boggus... */
 356 err:
 357         return -1;
 358 }
 359
 360 static struct mips_frame_info schedule_mfi __read_mostly;
 361
 362 #ifdef CONFIG_KALLSYMS
 363 static unsigned long get___schedule_addr(void)
 364 {
 365         return kallsyms_lookup_name("__schedule");
 366 }
 367 #else
 368 static unsigned long get___schedule_addr(void)
 369 {
 370         union mips_instruction *ip = (void *)schedule;
 371         int max_insns = 8;
 372         int i;
 373
 374         for (i = 0; i < max_insns; i++, ip++) {
 375                 if (ip->j_format.opcode == j_op)
 376                         return J_TARGET(ip, ip->j_format.target);
 377         }
 378         return 0;
 379 }
 380 #endif
 381
 382 static int __init frame_info_init(void)
 383 {
 384         unsigned long size = 0;
 385 #ifdef CONFIG_KALLSYMS
 386         unsigned long ofs;
 387 #endif
 388         unsigned long addr;
 389
 390         addr = get___schedule_addr();
 391         if (!addr)
 392                 addr = (unsigned long)schedule;
 393
 394 #ifdef CONFIG_KALLSYMS
 395         kallsyms_lookup_size_offset(addr, &size, &ofs);
 396 #endif
 397         schedule_mfi.func = (void *)addr;
 398         schedule_mfi.func_size = size;
 399
 400         get_frame_info(&schedule_mfi);
 401
 402         /*
 403          * Without schedule() frame info, result given by
 404          * thread_saved_pc() and get_wchan() are not reliable.
 405          */
 406         if (schedule_mfi.pc_offset < 0)
 407                 printk("Can't analyze schedule() prologue at %p\n", schedule);
 408
 409         return 0;
 410 }
 411
 412 arch_initcall(frame_info_init);
 413
 414 /*
 415  * Return saved PC of a blocked thread.
 416  */
 417 unsigned long thread_saved_pc(struct task_struct *tsk)
 418 {
 419         struct thread_struct *t = &tsk->thread;
 420
 421         /* New born processes are a special case */
 422         if (t->reg31 == (unsigned long) ret_from_fork)
 423                 return t->reg31;
 424         if (schedule_mfi.pc_offset < 0)
 425                 return 0;
 426         return ((unsigned long *)t->reg29)[schedule_mfi.pc_offset];
 427 }
 428
 429
 430 #ifdef CONFIG_KALLSYMS
 431 /* generic stack unwinding function */
 432 unsigned long notrace unwind_stack_by_address(unsigned long stack_page,
 433                                               unsigned long *sp,
 434                                               unsigned long pc,
 435                                               unsigned long *ra)
 436 {
 437         struct mips_frame_info info;
 438         unsigned long size, ofs;
 439         int leaf;
 440         extern void ret_from_irq(void);
 441         extern void ret_from_exception(void);
 442
 443         if (!stack_page)
 444                 return 0;
 445
 446         /*
 447          * If we reached the bottom of interrupt context,
 448          * return saved pc in pt_regs.
 449          */
 450         if (pc == (unsigned long)ret_from_irq ||
 451             pc == (unsigned long)ret_from_exception) {
 452                 struct pt_regs *regs;
 453                 if (*sp >= stack_page &&
 454                     *sp + sizeof(*regs) <= stack_page + THREAD_SIZE - 32) {
 455                         regs = (struct pt_regs *)*sp;
 456                         pc = regs->cp0_epc;
 457                         if (!user_mode(regs) && __kernel_text_address(pc)) {
 458                                 *sp = regs->regs[29];
 459                                 *ra = regs->regs[31];
 460                                 return pc;
 461                         }
 462                 }
 463                 return 0;
 464         }
 465         if (!kallsyms_lookup_size_offset(pc, &size, &ofs))
 466                 return 0;
 467         /*
 468          * Return ra if an exception occurred at the first instruction
 469          */
 470         if (unlikely(ofs == 0)) {
 471                 pc = *ra;
 472                 *ra = 0;
 473                 return pc;
 474         }
 475
 476         info.func = (void *)(pc - ofs);
 477         info.func_size = ofs;   /* analyze from start to ofs */
 478         leaf = get_frame_info(&info);
 479         if (leaf < 0)
 480                 return 0;
 481
 482         if (*sp < stack_page ||
 483             *sp + info.frame_size > stack_page + THREAD_SIZE - 32)
 484                 return 0;
 485
 486         if (leaf)
 487                 /*
 488                  * For some extreme cases, get_frame_info() can
 489                  * consider wrongly a nested function as a leaf
 490                  * one. In that cases avoid to return always the
 491                  * same value.
 492                  */
 493                 pc = pc != *ra ? *ra : 0;
 494         else
 495                 pc = ((unsigned long *)(*sp))[info.pc_offset];
 496
 497         *sp += info.frame_size;
 498         *ra = 0;
 499         return __kernel_text_address(pc) ? pc : 0;
 500 }
 501 EXPORT_SYMBOL(unwind_stack_by_address);
 502
 503 /* used by show_backtrace() */
 504 unsigned long unwind_stack(struct task_struct *task, unsigned long *sp,
 505                            unsigned long pc, unsigned long *ra)
 506 {
 507         unsigned long stack_page = (unsigned long)task_stack_page(task);
 508         return unwind_stack_by_address(stack_page, sp, pc, ra);
 509 }
 510 #endif
 511
 512 /*
 513  * get_wchan - a maintenance nightmare^W^Wpain in the ass ...
 514  */
 515 unsigned long get_wchan(struct task_struct *task)
 516 {
 517         unsigned long pc = 0;
 518 #ifdef CONFIG_KALLSYMS
 519         unsigned long sp;
 520         unsigned long ra = 0;
 521 #endif
 522
 523         if (!task || task == current || task->state == TASK_RUNNING)
 524                 goto out;
 525         if (!task_stack_page(task))
 526                 goto out;
 527
 528         pc = thread_saved_pc(task);
 529
 530 #ifdef CONFIG_KALLSYMS
 531         sp = task->thread.reg29 + schedule_mfi.frame_size;
 532
 533         while (in_sched_functions(pc))
 534                 pc = unwind_stack(task, &sp, pc, &ra);
 535 #endif
 536
 537 out:
 538         return pc;
 539 }
 540
 541 /*
 542  * Don't forget that the stack pointer must be aligned on a 8 bytes
 543  * boundary for 32-bits ABI and 16 bytes for 64-bits ABI.
 544  */
 545 unsigned long arch_align_stack(unsigned long sp)
 546 {
 547         if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
 548                 sp -= get_random_int() & ~PAGE_MASK;
 549
 550         return sp & ALMASK;
 551 }
 552
 553 static void arch_dump_stack(void *info)
 554 {
 555         struct pt_regs *regs;
 556
 557         regs = get_irq_regs();
 558
 559         if (regs)
 560                 show_regs(regs);
 561
 562         dump_stack();
 563 }
 564
 565 void arch_trigger_all_cpu_backtrace(bool include_self)
 566 {
 567         smp_call_function(arch_dump_stack, NULL, 1);
 568 }
 569
 570 int mips_get_process_fp_mode(struct task_struct *task)
 571 {
 572         int value = 0;
 573
 574         if (!test_tsk_thread_flag(task, TIF_32BIT_FPREGS))
 575                 value |= PR_FP_MODE_FR;
 576         if (test_tsk_thread_flag(task, TIF_HYBRID_FPREGS))
 577                 value |= PR_FP_MODE_FRE;
 578
 579         return value;
 580 }
 581
 582 int mips_set_process_fp_mode(struct task_struct *task, unsigned int value)
 583 {
 584         const unsigned int known_bits = PR_FP_MODE_FR | PR_FP_MODE_FRE;
 585         unsigned long switch_count;
 586         struct task_struct *t;
 587
 588         /* Check the value is valid */
 589         if (value & ~known_bits)
 590                 return -EOPNOTSUPP;
 591
 592         /* Avoid inadvertently triggering emulation */
 593         if ((value & PR_FP_MODE_FR) && raw_cpu_has_fpu &&
 594             !(raw_current_cpu_data.fpu_id & MIPS_FPIR_F64))
 595                 return -EOPNOTSUPP;
 596         if ((value & PR_FP_MODE_FRE) && raw_cpu_has_fpu && !cpu_has_fre)
 597                 return -EOPNOTSUPP;
 598
 599         /* FR = 0 not supported in MIPS R6 */
 600         if (!(value & PR_FP_MODE_FR) && raw_cpu_has_fpu && cpu_has_mips_r6)
 601                 return -EOPNOTSUPP;
 602
 603         /* Proceed with the mode switch */
 604         preempt_disable();
 605
 606         /* Save FP & vector context, then disable FPU & MSA */
 607         if (task->signal == current->signal)
 608                 lose_fpu(1);
 609
 610         /* Prevent any threads from obtaining live FP context */
 611         atomic_set(&task->mm->context.fp_mode_switching, 1);
 612         smp_mb__after_atomic();
 613
 614         /*
 615          * If there are multiple online CPUs then wait until all threads whose
 616          * FP mode is about to change have been context switched. This approach
 617          * allows us to only worry about whether an FP mode switch is in
 618          * progress when FP is first used in a tasks time slice. Pretty much all
 619          * of the mode switch overhead can thus be confined to cases where mode
 620          * switches are actually occuring. That is, to here. However for the
 621          * thread performing the mode switch it may take a while...
 622          */
 623         if (num_online_cpus() > 1) {
 624                 spin_lock_irq(&task->sighand->siglock);
 625
 626                 for_each_thread(task, t) {
 627                         if (t == current)
 628                                 continue;
 629
 630                         switch_count = t->nvcsw + t->nivcsw;
 631
 632                         do {
 633                                 spin_unlock_irq(&task->sighand->siglock);
 634                                 cond_resched();
 635                                 spin_lock_irq(&task->sighand->siglock);
 636                         } while ((t->nvcsw + t->nivcsw) == switch_count);
 637                 }
 638
 639                 spin_unlock_irq(&task->sighand->siglock);
 640         }
 641
 642         /*
 643          * There are now no threads of the process with live FP context, so it
 644          * is safe to proceed with the FP mode switch.
 645          */
 646         for_each_thread(task, t) {
 647                 /* Update desired FP register width */
 648                 if (value & PR_FP_MODE_FR) {
 649                         clear_tsk_thread_flag(t, TIF_32BIT_FPREGS);
 650                 } else {
 651                         set_tsk_thread_flag(t, TIF_32BIT_FPREGS);
 652                         clear_tsk_thread_flag(t, TIF_MSA_CTX_LIVE);
 653                 }
 654
 655                 /* Update desired FP single layout */
 656                 if (value & PR_FP_MODE_FRE)
 657                         set_tsk_thread_flag(t, TIF_HYBRID_FPREGS);
 658                 else
 659                         clear_tsk_thread_flag(t, TIF_HYBRID_FPREGS);
 660         }
 661
 662         /* Allow threads to use FP again */
 663         atomic_set(&task->mm->context.fp_mode_switching, 0);
 664         preempt_enable();
 665
 666         return 0;
 667 }