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TOMOYO Linux Cross Reference
Linux/arch/mips/kernel/process.c

Version: ~ [ linux-5.2-rc1 ] ~ [ linux-5.1.2 ] ~ [ linux-5.0.16 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.43 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.119 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.176 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.179 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.139 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.67 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.39.4 ] ~ [ linux-2.6.38.8 ] ~ [ linux-2.6.37.6 ] ~ [ linux-2.6.36.4 ] ~ [ linux-2.6.35.14 ] ~ [ linux-2.6.34.15 ] ~ [ linux-2.6.33.20 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

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

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