arch/x86/kernel/fpu/init.c

   1 /*
   2  * x86 FPU boot time init code:
   3  */
   4 #include <asm/fpu/internal.h>
   5 #include <asm/tlbflush.h>
   6 #include <asm/setup.h>
   7 #include <asm/cmdline.h>
   8
   9 #include <linux/sched.h>
  10 #include <linux/init.h>
  11
  12 /*
  13  * Initialize the registers found in all CPUs, CR0 and CR4:
  14  */
  15 static void fpu__init_cpu_generic(void)
  16 {
  17         unsigned long cr0;
  18         unsigned long cr4_mask = 0;
  19
  20         if (boot_cpu_has(X86_FEATURE_FXSR))
  21                 cr4_mask |= X86_CR4_OSFXSR;
  22         if (boot_cpu_has(X86_FEATURE_XMM))
  23                 cr4_mask |= X86_CR4_OSXMMEXCPT;
  24         if (cr4_mask)
  25                 cr4_set_bits(cr4_mask);
  26
  27         cr0 = read_cr0();
  28         cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
  29         if (!boot_cpu_has(X86_FEATURE_FPU))
  30                 cr0 |= X86_CR0_EM;
  31         write_cr0(cr0);
  32
  33         /* Flush out any pending x87 state: */
  34 #ifdef CONFIG_MATH_EMULATION
  35         if (!boot_cpu_has(X86_FEATURE_FPU))
  36                 fpstate_init_soft(&current->thread.fpu.state.soft);
  37         else
  38 #endif
  39                 asm volatile ("fninit");
  40 }
  41
  42 /*
  43  * Enable all supported FPU features. Called when a CPU is brought online:
  44  */
  45 void fpu__init_cpu(void)
  46 {
  47         fpu__init_cpu_generic();
  48         fpu__init_cpu_xstate();
  49 }
  50
  51 /*
  52  * The earliest FPU detection code.
  53  *
  54  * Set the X86_FEATURE_FPU CPU-capability bit based on
  55  * trying to execute an actual sequence of FPU instructions:
  56  */
  57 static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
  58 {
  59         unsigned long cr0;
  60         u16 fsw, fcw;
  61
  62         fsw = fcw = 0xffff;
  63
  64         cr0 = read_cr0();
  65         cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
  66         write_cr0(cr0);
  67
  68         if (!test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
  69                 asm volatile("fninit ; fnstsw %0 ; fnstcw %1"
  70                              : "+m" (fsw), "+m" (fcw));
  71
  72                 if (fsw == 0 && (fcw & 0x103f) == 0x003f)
  73                         set_cpu_cap(c, X86_FEATURE_FPU);
  74                 else
  75                         clear_cpu_cap(c, X86_FEATURE_FPU);
  76         }
  77
  78 #ifndef CONFIG_MATH_EMULATION
  79         if (!boot_cpu_has(X86_FEATURE_FPU)) {
  80                 pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
  81                 for (;;)
  82                         asm volatile("hlt");
  83         }
  84 #endif
  85 }
  86
  87 /*
  88  * Boot time FPU feature detection code:
  89  */
  90 unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
  91
  92 static void __init fpu__init_system_mxcsr(void)
  93 {
  94         unsigned int mask = 0;
  95
  96         if (boot_cpu_has(X86_FEATURE_FXSR)) {
  97                 /* Static because GCC does not get 16-byte stack alignment right: */
  98                 static struct fxregs_state fxregs __initdata;
  99
 100                 asm volatile("fxsave %0" : "+m" (fxregs));
 101
 102                 mask = fxregs.mxcsr_mask;
 103
 104                 /*
 105                  * If zero then use the default features mask,
 106                  * which has all features set, except the
 107                  * denormals-are-zero feature bit:
 108                  */
 109                 if (mask == 0)
 110                         mask = 0x0000ffbf;
 111         }
 112         mxcsr_feature_mask &= mask;
 113 }
 114
 115 /*
 116  * Once per bootup FPU initialization sequences that will run on most x86 CPUs:
 117  */
 118 static void __init fpu__init_system_generic(void)
 119 {
 120         /*
 121          * Set up the legacy init FPU context. (xstate init might overwrite this
 122          * with a more modern format, if the CPU supports it.)
 123          */
 124         fpstate_init(&init_fpstate);
 125
 126         fpu__init_system_mxcsr();
 127 }
 128
 129 /*
 130  * Size of the FPU context state. All tasks in the system use the
 131  * same context size, regardless of what portion they use.
 132  * This is inherent to the XSAVE architecture which puts all state
 133  * components into a single, continuous memory block:
 134  */
 135 unsigned int fpu_kernel_xstate_size;
 136 EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);
 137
 138 /* Get alignment of the TYPE. */
 139 #define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
 140
 141 /*
 142  * Enforce that 'MEMBER' is the last field of 'TYPE'.
 143  *
 144  * Align the computed size with alignment of the TYPE,
 145  * because that's how C aligns structs.
 146  */
 147 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
 148         BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
 149                                            TYPE_ALIGN(TYPE)))
 150
 151 /*
 152  * We append the 'struct fpu' to the task_struct:
 153  */
 154 static void __init fpu__init_task_struct_size(void)
 155 {
 156         int task_size = sizeof(struct task_struct);
 157
 158         /*
 159          * Subtract off the static size of the register state.
 160          * It potentially has a bunch of padding.
 161          */
 162         task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);
 163
 164         /*
 165          * Add back the dynamically-calculated register state
 166          * size.
 167          */
 168         task_size += fpu_kernel_xstate_size;
 169
 170         /*
 171          * We dynamically size 'struct fpu', so we require that
 172          * it be at the end of 'thread_struct' and that
 173          * 'thread_struct' be at the end of 'task_struct'.  If
 174          * you hit a compile error here, check the structure to
 175          * see if something got added to the end.
 176          */
 177         CHECK_MEMBER_AT_END_OF(struct fpu, state);
 178         CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
 179         CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
 180
 181         arch_task_struct_size = task_size;
 182 }
 183
 184 /*
 185  * Set up the user and kernel xstate sizes based on the legacy FPU context size.
 186  *
 187  * We set this up first, and later it will be overwritten by
 188  * fpu__init_system_xstate() if the CPU knows about xstates.
 189  */
 190 static void __init fpu__init_system_xstate_size_legacy(void)
 191 {
 192         static int on_boot_cpu __initdata = 1;
 193
 194         WARN_ON_FPU(!on_boot_cpu);
 195         on_boot_cpu = 0;
 196
 197         /*
 198          * Note that xstate sizes might be overwritten later during
 199          * fpu__init_system_xstate().
 200          */
 201
 202         if (!boot_cpu_has(X86_FEATURE_FPU)) {
 203                 /*
 204                  * Disable xsave as we do not support it if i387
 205                  * emulation is enabled.
 206                  */
 207                 setup_clear_cpu_cap(X86_FEATURE_XSAVE);
 208                 setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
 209                 fpu_kernel_xstate_size = sizeof(struct swregs_state);
 210         } else {
 211                 if (boot_cpu_has(X86_FEATURE_FXSR))
 212                         fpu_kernel_xstate_size =
 213                                 sizeof(struct fxregs_state);
 214                 else
 215                         fpu_kernel_xstate_size =
 216                                 sizeof(struct fregs_state);
 217         }
 218
 219         fpu_user_xstate_size = fpu_kernel_xstate_size;
 220 }
 221
 222 /*
 223  * Find supported xfeatures based on cpu features and command-line input.
 224  * This must be called after fpu__init_parse_early_param() is called and
 225  * xfeatures_mask is enumerated.
 226  */
 227 u64 __init fpu__get_supported_xfeatures_mask(void)
 228 {
 229         return XCNTXT_MASK;
 230 }
 231
 232 /* Legacy code to initialize eager fpu mode. */
 233 static void __init fpu__init_system_ctx_switch(void)
 234 {
 235         static bool on_boot_cpu __initdata = 1;
 236
 237         WARN_ON_FPU(!on_boot_cpu);
 238         on_boot_cpu = 0;
 239
 240         WARN_ON_FPU(current->thread.fpu.fpstate_active);
 241 }
 242
 243 /*
 244  * We parse fpu parameters early because fpu__init_system() is executed
 245  * before parse_early_param().
 246  */
 247 static void __init fpu__init_parse_early_param(void)
 248 {
 249         if (cmdline_find_option_bool(boot_command_line, "no387"))
 250                 setup_clear_cpu_cap(X86_FEATURE_FPU);
 251
 252         if (cmdline_find_option_bool(boot_command_line, "nofxsr")) {
 253                 setup_clear_cpu_cap(X86_FEATURE_FXSR);
 254                 setup_clear_cpu_cap(X86_FEATURE_FXSR_OPT);
 255                 setup_clear_cpu_cap(X86_FEATURE_XMM);
 256         }
 257
 258         if (cmdline_find_option_bool(boot_command_line, "noxsave"))
 259                 fpu__xstate_clear_all_cpu_caps();
 260
 261         if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
 262                 setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
 263
 264         if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
 265                 setup_clear_cpu_cap(X86_FEATURE_XSAVES);
 266 }
 267
 268 /*
 269  * Called on the boot CPU once per system bootup, to set up the initial
 270  * FPU state that is later cloned into all processes:
 271  */
 272 void __init fpu__init_system(struct cpuinfo_x86 *c)
 273 {
 274         fpu__init_parse_early_param();
 275         fpu__init_system_early_generic(c);
 276
 277         /*
 278          * The FPU has to be operational for some of the
 279          * later FPU init activities:
 280          */
 281         fpu__init_cpu();
 282
 283         fpu__init_system_generic();
 284         fpu__init_system_xstate_size_legacy();
 285         fpu__init_system_xstate();
 286         fpu__init_task_struct_size();
 287
 288         fpu__init_system_ctx_switch();
 289 }