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