arch/x86/kernel/i387.c

   1 /*
   2  *  Copyright (C) 1994 Linus Torvalds
   3  *
   4  *  Pentium III FXSR, SSE support
   5  *  General FPU state handling cleanups
   6  *      Gareth Hughes <gareth@valinux.com>, May 2000
   7  */
   8 #include <linux/module.h>
   9 #include <linux/regset.h>
  10 #include <linux/sched.h>
  11 #include <linux/slab.h>
  12
  13 #include <asm/sigcontext.h>
  14 #include <asm/processor.h>
  15 #include <asm/math_emu.h>
  16 #include <asm/uaccess.h>
  17 #include <asm/ptrace.h>
  18 #include <asm/i387.h>
  19 #include <asm/fpu-internal.h>
  20 #include <asm/user.h>
  21
  22 /*
  23  * Were we in an interrupt that interrupted kernel mode?
  24  *
  25  * On others, we can do a kernel_fpu_begin/end() pair *ONLY* if that
  26  * pair does nothing at all: the thread must not have fpu (so
  27  * that we don't try to save the FPU state), and TS must
  28  * be set (so that the clts/stts pair does nothing that is
  29  * visible in the interrupted kernel thread).
  30  *
  31  * Except for the eagerfpu case when we return 1 unless we've already
  32  * been eager and saved the state in kernel_fpu_begin().
  33  */
  34 static inline bool interrupted_kernel_fpu_idle(void)
  35 {
  36         if (use_eager_fpu())
  37                 return __thread_has_fpu(current);
  38
  39         return !__thread_has_fpu(current) &&
  40                 (read_cr0() & X86_CR0_TS);
  41 }
  42
  43 /*
  44  * Were we in user mode (or vm86 mode) when we were
  45  * interrupted?
  46  *
  47  * Doing kernel_fpu_begin/end() is ok if we are running
  48  * in an interrupt context from user mode - we'll just
  49  * save the FPU state as required.
  50  */
  51 static inline bool interrupted_user_mode(void)
  52 {
  53         struct pt_regs *regs = get_irq_regs();
  54         return regs && user_mode_vm(regs);
  55 }
  56
  57 /*
  58  * Can we use the FPU in kernel mode with the
  59  * whole "kernel_fpu_begin/end()" sequence?
  60  *
  61  * It's always ok in process context (ie "not interrupt")
  62  * but it is sometimes ok even from an irq.
  63  */
  64 bool irq_fpu_usable(void)
  65 {
  66         return !in_interrupt() ||
  67                 interrupted_user_mode() ||
  68                 interrupted_kernel_fpu_idle();
  69 }
  70 EXPORT_SYMBOL(irq_fpu_usable);
  71
  72 void __kernel_fpu_begin(void)
  73 {
  74         struct task_struct *me = current;
  75
  76         if (__thread_has_fpu(me)) {
  77                 __thread_clear_has_fpu(me);
  78                 __save_init_fpu(me);
  79                 /* We do 'stts()' in __kernel_fpu_end() */
  80         } else if (!use_eager_fpu()) {
  81                 this_cpu_write(fpu_owner_task, NULL);
  82                 clts();
  83         }
  84 }
  85 EXPORT_SYMBOL(__kernel_fpu_begin);
  86
  87 void __kernel_fpu_end(void)
  88 {
  89         if (use_eager_fpu()) {
  90                 /*
  91                  * For eager fpu, most the time, tsk_used_math() is true.
  92                  * Restore the user math as we are done with the kernel usage.
  93                  * At few instances during thread exit, signal handling etc,
  94                  * tsk_used_math() is false. Those few places will take proper
  95                  * actions, so we don't need to restore the math here.
  96                  */
  97                 if (likely(tsk_used_math(current)))
  98                         math_state_restore();
  99         } else {
 100                 stts();
 101         }
 102 }
 103 EXPORT_SYMBOL(__kernel_fpu_end);
 104
 105 void unlazy_fpu(struct task_struct *tsk)
 106 {
 107         preempt_disable();
 108         if (__thread_has_fpu(tsk)) {
 109                 __save_init_fpu(tsk);
 110                 __thread_fpu_end(tsk);
 111         } else
 112                 tsk->fpu_counter = 0;
 113         preempt_enable();
 114 }
 115 EXPORT_SYMBOL(unlazy_fpu);
 116
 117 unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
 118 unsigned int xstate_size;
 119 EXPORT_SYMBOL_GPL(xstate_size);
 120 static struct i387_fxsave_struct fx_scratch __cpuinitdata;
 121
 122 static void __cpuinit mxcsr_feature_mask_init(void)
 123 {
 124         unsigned long mask = 0;
 125
 126         if (cpu_has_fxsr) {
 127                 memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct));
 128                 asm volatile("fxsave %0" : "+m" (fx_scratch));
 129                 mask = fx_scratch.mxcsr_mask;
 130                 if (mask == 0)
 131                         mask = 0x0000ffbf;
 132         }
 133         mxcsr_feature_mask &= mask;
 134 }
 135
 136 static void __cpuinit init_thread_xstate(void)
 137 {
 138         /*
 139          * Note that xstate_size might be overwriten later during
 140          * xsave_init().
 141          */
 142
 143         if (!HAVE_HWFP) {
 144                 /*
 145                  * Disable xsave as we do not support it if i387
 146                  * emulation is enabled.
 147                  */
 148                 setup_clear_cpu_cap(X86_FEATURE_XSAVE);
 149                 setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
 150                 xstate_size = sizeof(struct i387_soft_struct);
 151                 return;
 152         }
 153
 154         if (cpu_has_fxsr)
 155                 xstate_size = sizeof(struct i387_fxsave_struct);
 156         else
 157                 xstate_size = sizeof(struct i387_fsave_struct);
 158 }
 159
 160 /*
 161  * Called at bootup to set up the initial FPU state that is later cloned
 162  * into all processes.
 163  */
 164
 165 void __cpuinit fpu_init(void)
 166 {
 167         unsigned long cr0;
 168         unsigned long cr4_mask = 0;
 169
 170         if (cpu_has_fxsr)
 171                 cr4_mask |= X86_CR4_OSFXSR;
 172         if (cpu_has_xmm)
 173                 cr4_mask |= X86_CR4_OSXMMEXCPT;
 174         if (cr4_mask)
 175                 set_in_cr4(cr4_mask);
 176
 177         cr0 = read_cr0();
 178         cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
 179         if (!HAVE_HWFP)
 180                 cr0 |= X86_CR0_EM;
 181         write_cr0(cr0);
 182
 183         /*
 184          * init_thread_xstate is only called once to avoid overriding
 185          * xstate_size during boot time or during CPU hotplug.
 186          */
 187         if (xstate_size == 0)
 188                 init_thread_xstate();
 189
 190         mxcsr_feature_mask_init();
 191         xsave_init();
 192         eager_fpu_init();
 193 }
 194
 195 void fpu_finit(struct fpu *fpu)
 196 {
 197         if (!HAVE_HWFP) {
 198                 finit_soft_fpu(&fpu->state->soft);
 199                 return;
 200         }
 201
 202         if (cpu_has_fxsr) {
 203                 fx_finit(&fpu->state->fxsave);
 204         } else {
 205                 struct i387_fsave_struct *fp = &fpu->state->fsave;
 206                 memset(fp, 0, xstate_size);
 207                 fp->cwd = 0xffff037fu;
 208                 fp->swd = 0xffff0000u;
 209                 fp->twd = 0xffffffffu;
 210                 fp->fos = 0xffff0000u;
 211         }
 212 }
 213 EXPORT_SYMBOL_GPL(fpu_finit);
 214
 215 /*
 216  * The _current_ task is using the FPU for the first time
 217  * so initialize it and set the mxcsr to its default
 218  * value at reset if we support XMM instructions and then
 219  * remember the current task has used the FPU.
 220  */
 221 int init_fpu(struct task_struct *tsk)
 222 {
 223         int ret;
 224
 225         if (tsk_used_math(tsk)) {
 226                 if (HAVE_HWFP && tsk == current)
 227                         unlazy_fpu(tsk);
 228                 tsk->thread.fpu.last_cpu = ~0;
 229                 return 0;
 230         }
 231
 232         /*
 233          * Memory allocation at the first usage of the FPU and other state.
 234          */
 235         ret = fpu_alloc(&tsk->thread.fpu);
 236         if (ret)
 237                 return ret;
 238
 239         fpu_finit(&tsk->thread.fpu);
 240
 241         set_stopped_child_used_math(tsk);
 242         return 0;
 243 }
 244 EXPORT_SYMBOL_GPL(init_fpu);
 245
 246 /*
 247  * The xstateregs_active() routine is the same as the fpregs_active() routine,
 248  * as the "regset->n" for the xstate regset will be updated based on the feature
 249  * capabilites supported by the xsave.
 250  */
 251 int fpregs_active(struct task_struct *target, const struct user_regset *regset)
 252 {
 253         return tsk_used_math(target) ? regset->n : 0;
 254 }
 255
 256 int xfpregs_active(struct task_struct *target, const struct user_regset *regset)
 257 {
 258         return (cpu_has_fxsr && tsk_used_math(target)) ? regset->n : 0;
 259 }
 260
 261 int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
 262                 unsigned int pos, unsigned int count,
 263                 void *kbuf, void __user *ubuf)
 264 {
 265         int ret;
 266
 267         if (!cpu_has_fxsr)
 268                 return -ENODEV;
 269
 270         ret = init_fpu(target);
 271         if (ret)
 272                 return ret;
 273
 274         sanitize_i387_state(target);
 275
 276         return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
 277                                    &target->thread.fpu.state->fxsave, 0, -1);
 278 }
 279
 280 int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 281                 unsigned int pos, unsigned int count,
 282                 const void *kbuf, const void __user *ubuf)
 283 {
 284         int ret;
 285
 286         if (!cpu_has_fxsr)
 287                 return -ENODEV;
 288
 289         ret = init_fpu(target);
 290         if (ret)
 291                 return ret;
 292
 293         sanitize_i387_state(target);
 294
 295         ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
 296                                  &target->thread.fpu.state->fxsave, 0, -1);
 297
 298         /*
 299          * mxcsr reserved bits must be masked to zero for security reasons.
 300          */
 301         target->thread.fpu.state->fxsave.mxcsr &= mxcsr_feature_mask;
 302
 303         /*
 304          * update the header bits in the xsave header, indicating the
 305          * presence of FP and SSE state.
 306          */
 307         if (cpu_has_xsave)
 308                 target->thread.fpu.state->xsave.xsave_hdr.xstate_bv |= XSTATE_FPSSE;
 309
 310         return ret;
 311 }
 312
 313 int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
 314                 unsigned int pos, unsigned int count,
 315                 void *kbuf, void __user *ubuf)
 316 {
 317         int ret;
 318
 319         if (!cpu_has_xsave)
 320                 return -ENODEV;
 321
 322         ret = init_fpu(target);
 323         if (ret)
 324                 return ret;
 325
 326         /*
 327          * Copy the 48bytes defined by the software first into the xstate
 328          * memory layout in the thread struct, so that we can copy the entire
 329          * xstateregs to the user using one user_regset_copyout().
 330          */
 331         memcpy(&target->thread.fpu.state->fxsave.sw_reserved,
 332                xstate_fx_sw_bytes, sizeof(xstate_fx_sw_bytes));
 333
 334         /*
 335          * Copy the xstate memory layout.
 336          */
 337         ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
 338                                   &target->thread.fpu.state->xsave, 0, -1);
 339         return ret;
 340 }
 341
 342 int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
 343                   unsigned int pos, unsigned int count,
 344                   const void *kbuf, const void __user *ubuf)
 345 {
 346         int ret;
 347         struct xsave_hdr_struct *xsave_hdr;
 348
 349         if (!cpu_has_xsave)
 350                 return -ENODEV;
 351
 352         ret = init_fpu(target);
 353         if (ret)
 354                 return ret;
 355
 356         ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
 357                                  &target->thread.fpu.state->xsave, 0, -1);
 358
 359         /*
 360          * mxcsr reserved bits must be masked to zero for security reasons.
 361          */
 362         target->thread.fpu.state->fxsave.mxcsr &= mxcsr_feature_mask;
 363
 364         xsave_hdr = &target->thread.fpu.state->xsave.xsave_hdr;
 365
 366         xsave_hdr->xstate_bv &= pcntxt_mask;
 367         /*
 368          * These bits must be zero.
 369          */
 370         xsave_hdr->reserved1[0] = xsave_hdr->reserved1[1] = 0;
 371
 372         return ret;
 373 }
 374
 375 #if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
 376
 377 /*
 378  * FPU tag word conversions.
 379  */
 380
 381 static inline unsigned short twd_i387_to_fxsr(unsigned short twd)
 382 {
 383         unsigned int tmp; /* to avoid 16 bit prefixes in the code */
 384
 385         /* Transform each pair of bits into 01 (valid) or 00 (empty) */
 386         tmp = ~twd;
 387         tmp = (tmp | (tmp>>1)) & 0x5555; /* 0V0V0V0V0V0V0V0V */
 388         /* and move the valid bits to the lower byte. */
 389         tmp = (tmp | (tmp >> 1)) & 0x3333; /* 00VV00VV00VV00VV */
 390         tmp = (tmp | (tmp >> 2)) & 0x0f0f; /* 0000VVVV0000VVVV */
 391         tmp = (tmp | (tmp >> 4)) & 0x00ff; /* 00000000VVVVVVVV */
 392
 393         return tmp;
 394 }
 395
 396 #define FPREG_ADDR(f, n)        ((void *)&(f)->st_space + (n) * 16)
 397 #define FP_EXP_TAG_VALID        0
 398 #define FP_EXP_TAG_ZERO         1
 399 #define FP_EXP_TAG_SPECIAL      2
 400 #define FP_EXP_TAG_EMPTY        3
 401
 402 static inline u32 twd_fxsr_to_i387(struct i387_fxsave_struct *fxsave)
 403 {
 404         struct _fpxreg *st;
 405         u32 tos = (fxsave->swd >> 11) & 7;
 406         u32 twd = (unsigned long) fxsave->twd;
 407         u32 tag;
 408         u32 ret = 0xffff0000u;
 409         int i;
 410
 411         for (i = 0; i < 8; i++, twd >>= 1) {
 412                 if (twd & 0x1) {
 413                         st = FPREG_ADDR(fxsave, (i - tos) & 7);
 414
 415                         switch (st->exponent & 0x7fff) {
 416                         case 0x7fff:
 417                                 tag = FP_EXP_TAG_SPECIAL;
 418                                 break;
 419                         case 0x0000:
 420                                 if (!st->significand[0] &&
 421                                     !st->significand[1] &&
 422                                     !st->significand[2] &&
 423                                     !st->significand[3])
 424                                         tag = FP_EXP_TAG_ZERO;
 425                                 else
 426                                         tag = FP_EXP_TAG_SPECIAL;
 427                                 break;
 428                         default:
 429                                 if (st->significand[3] & 0x8000)
 430                                         tag = FP_EXP_TAG_VALID;
 431                                 else
 432                                         tag = FP_EXP_TAG_SPECIAL;
 433                                 break;
 434                         }
 435                 } else {
 436                         tag = FP_EXP_TAG_EMPTY;
 437                 }
 438                 ret |= tag << (2 * i);
 439         }
 440         return ret;
 441 }
 442
 443 /*
 444  * FXSR floating point environment conversions.
 445  */
 446
 447 void
 448 convert_from_fxsr(struct user_i387_ia32_struct *env, struct task_struct *tsk)
 449 {
 450         struct i387_fxsave_struct *fxsave = &tsk->thread.fpu.state->fxsave;
 451         struct _fpreg *to = (struct _fpreg *) &env->st_space[0];
 452         struct _fpxreg *from = (struct _fpxreg *) &fxsave->st_space[0];
 453         int i;
 454
 455         env->cwd = fxsave->cwd | 0xffff0000u;
 456         env->swd = fxsave->swd | 0xffff0000u;
 457         env->twd = twd_fxsr_to_i387(fxsave);
 458
 459 #ifdef CONFIG_X86_64
 460         env->fip = fxsave->rip;
 461         env->foo = fxsave->rdp;
 462         /*
 463          * should be actually ds/cs at fpu exception time, but
 464          * that information is not available in 64bit mode.
 465          */
 466         env->fcs = task_pt_regs(tsk)->cs;
 467         if (tsk == current) {
 468                 savesegment(ds, env->fos);
 469         } else {
 470                 env->fos = tsk->thread.ds;
 471         }
 472         env->fos |= 0xffff0000;
 473 #else
 474         env->fip = fxsave->fip;
 475         env->fcs = (u16) fxsave->fcs | ((u32) fxsave->fop << 16);
 476         env->foo = fxsave->foo;
 477         env->fos = fxsave->fos;
 478 #endif
 479
 480         for (i = 0; i < 8; ++i)
 481                 memcpy(&to[i], &from[i], sizeof(to[0]));
 482 }
 483
 484 void convert_to_fxsr(struct task_struct *tsk,
 485                      const struct user_i387_ia32_struct *env)
 486
 487 {
 488         struct i387_fxsave_struct *fxsave = &tsk->thread.fpu.state->fxsave;
 489         struct _fpreg *from = (struct _fpreg *) &env->st_space[0];
 490         struct _fpxreg *to = (struct _fpxreg *) &fxsave->st_space[0];
 491         int i;
 492
 493         fxsave->cwd = env->cwd;
 494         fxsave->swd = env->swd;
 495         fxsave->twd = twd_i387_to_fxsr(env->twd);
 496         fxsave->fop = (u16) ((u32) env->fcs >> 16);
 497 #ifdef CONFIG_X86_64
 498         fxsave->rip = env->fip;
 499         fxsave->rdp = env->foo;
 500         /* cs and ds ignored */
 501 #else
 502         fxsave->fip = env->fip;
 503         fxsave->fcs = (env->fcs & 0xffff);
 504         fxsave->foo = env->foo;
 505         fxsave->fos = env->fos;
 506 #endif
 507
 508         for (i = 0; i < 8; ++i)
 509                 memcpy(&to[i], &from[i], sizeof(from[0]));
 510 }
 511
 512 int fpregs_get(struct task_struct *target, const struct user_regset *regset,
 513                unsigned int pos, unsigned int count,
 514                void *kbuf, void __user *ubuf)
 515 {
 516         struct user_i387_ia32_struct env;
 517         int ret;
 518
 519         ret = init_fpu(target);
 520         if (ret)
 521                 return ret;
 522
 523         if (!HAVE_HWFP)
 524                 return fpregs_soft_get(target, regset, pos, count, kbuf, ubuf);
 525
 526         if (!cpu_has_fxsr) {
 527                 return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
 528                                            &target->thread.fpu.state->fsave, 0,
 529                                            -1);
 530         }
 531
 532         sanitize_i387_state(target);
 533
 534         if (kbuf && pos == 0 && count == sizeof(env)) {
 535                 convert_from_fxsr(kbuf, target);
 536                 return 0;
 537         }
 538
 539         convert_from_fxsr(&env, target);
 540
 541         return user_regset_copyout(&pos, &count, &kbuf, &ubuf, &env, 0, -1);
 542 }
 543
 544 int fpregs_set(struct task_struct *target, const struct user_regset *regset,
 545                unsigned int pos, unsigned int count,
 546                const void *kbuf, const void __user *ubuf)
 547 {
 548         struct user_i387_ia32_struct env;
 549         int ret;
 550
 551         ret = init_fpu(target);
 552         if (ret)
 553                 return ret;
 554
 555         sanitize_i387_state(target);
 556
 557         if (!HAVE_HWFP)
 558                 return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf);
 559
 560         if (!cpu_has_fxsr) {
 561                 return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
 562                                           &target->thread.fpu.state->fsave, 0, -1);
 563         }
 564
 565         if (pos > 0 || count < sizeof(env))
 566                 convert_from_fxsr(&env, target);
 567
 568         ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &env, 0, -1);
 569         if (!ret)
 570                 convert_to_fxsr(target, &env);
 571
 572         /*
 573          * update the header bit in the xsave header, indicating the
 574          * presence of FP.
 575          */
 576         if (cpu_has_xsave)
 577                 target->thread.fpu.state->xsave.xsave_hdr.xstate_bv |= XSTATE_FP;
 578         return ret;
 579 }
 580
 581 /*
 582  * FPU state for core dumps.
 583  * This is only used for a.out dumps now.
 584  * It is declared generically using elf_fpregset_t (which is
 585  * struct user_i387_struct) but is in fact only used for 32-bit
 586  * dumps, so on 64-bit it is really struct user_i387_ia32_struct.
 587  */
 588 int dump_fpu(struct pt_regs *regs, struct user_i387_struct *fpu)
 589 {
 590         struct task_struct *tsk = current;
 591         int fpvalid;
 592
 593         fpvalid = !!used_math();
 594         if (fpvalid)
 595                 fpvalid = !fpregs_get(tsk, NULL,
 596                                       0, sizeof(struct user_i387_ia32_struct),
 597                                       fpu, NULL);
 598
 599         return fpvalid;
 600 }
 601 EXPORT_SYMBOL(dump_fpu);
 602
 603 #endif  /* CONFIG_X86_32 || CONFIG_IA32_EMULATION */