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/sched/task.h>
  11 #include <linux/init.h>
  12
  13 /*
  14  * Initialize the registers found in all CPUs, CR0 and CR4:
  15  */
  16 static void fpu__init_cpu_generic(void)
  17 {
  18         unsigned long cr0;
  19         unsigned long cr4_mask = 0;
  20
  21         if (boot_cpu_has(X86_FEATURE_FXSR))
  22                 cr4_mask |= X86_CR4_OSFXSR;
  23         if (boot_cpu_has(X86_FEATURE_XMM))
  24                 cr4_mask |= X86_CR4_OSXMMEXCPT;
  25         if (cr4_mask)
  26                 cr4_set_bits(cr4_mask);
  27
  28         cr0 = read_cr0();
  29         cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
  30         if (!boot_cpu_has(X86_FEATURE_FPU))
  31                 cr0 |= X86_CR0_EM;
  32         write_cr0(cr0);
  33
  34         /* Flush out any pending x87 state: */
  35 #ifdef CONFIG_MATH_EMULATION
  36         if (!boot_cpu_has(X86_FEATURE_FPU))
  37                 fpstate_init_soft(&current->thread.fpu.state.soft);
  38         else
  39 #endif
  40                 asm volatile ("fninit");
  41 }
  42
  43 /*
  44  * Enable all supported FPU features. Called when a CPU is brought online:
  45  */
  46 void fpu__init_cpu(void)
  47 {
  48         fpu__init_cpu_generic();
  49         fpu__init_cpu_xstate();
  50 }
  51
  52 static bool fpu__probe_without_cpuid(void)
  53 {
  54         unsigned long cr0;
  55         u16 fsw, fcw;
  56
  57         fsw = fcw = 0xffff;
  58
  59         cr0 = read_cr0();
  60         cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
  61         write_cr0(cr0);
  62
  63         asm volatile("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));
  64
  65         pr_info("x86/fpu: Probing for FPU: FSW=0x%04hx FCW=0x%04hx\n", fsw, fcw);
  66
  67         return fsw == 0 && (fcw & 0x103f) == 0x003f;
  68 }
  69
  70 static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
  71 {
  72         if (!boot_cpu_has(X86_FEATURE_CPUID) &&
  73             !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
  74                 if (fpu__probe_without_cpuid())
  75                         setup_force_cpu_cap(X86_FEATURE_FPU);
  76                 else
  77                         setup_clear_cpu_cap(X86_FEATURE_FPU);
  78         }
  79
  80 #ifndef CONFIG_MATH_EMULATION
  81         if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_FPU)) {
  82                 pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
  83                 for (;;)
  84                         asm volatile("hlt");
  85         }
  86 #endif
  87 }
  88
  89 /*
  90  * Boot time FPU feature detection code:
  91  */
  92 unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
  93
  94 static void __init fpu__init_system_mxcsr(void)
  95 {
  96         unsigned int mask = 0;
  97
  98         if (boot_cpu_has(X86_FEATURE_FXSR)) {
  99                 /* Static because GCC does not get 16-byte stack alignment right: */
 100                 static struct fxregs_state fxregs __initdata;
 101
 102                 asm volatile("fxsave %0" : "+m" (fxregs));
 103
 104                 mask = fxregs.mxcsr_mask;
 105
 106                 /*
 107                  * If zero then use the default features mask,
 108                  * which has all features set, except the
 109                  * denormals-are-zero feature bit:
 110                  */
 111                 if (mask == 0)
 112                         mask = 0x0000ffbf;
 113         }
 114         mxcsr_feature_mask &= mask;
 115 }
 116
 117 /*
 118  * Once per bootup FPU initialization sequences that will run on most x86 CPUs:
 119  */
 120 static void __init fpu__init_system_generic(void)
 121 {
 122         /*
 123          * Set up the legacy init FPU context. (xstate init might overwrite this
 124          * with a more modern format, if the CPU supports it.)
 125          */
 126         fpstate_init(&init_fpstate);
 127
 128         fpu__init_system_mxcsr();
 129 }
 130
 131 /*
 132  * Size of the FPU context state. All tasks in the system use the
 133  * same context size, regardless of what portion they use.
 134  * This is inherent to the XSAVE architecture which puts all state
 135  * components into a single, continuous memory block:
 136  */
 137 unsigned int fpu_kernel_xstate_size;
 138 EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);
 139
 140 /* Get alignment of the TYPE. */
 141 #define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
 142
 143 /*
 144  * Enforce that 'MEMBER' is the last field of 'TYPE'.
 145  *
 146  * Align the computed size with alignment of the TYPE,
 147  * because that's how C aligns structs.
 148  */
 149 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
 150         BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
 151                                            TYPE_ALIGN(TYPE)))
 152
 153 /*
 154  * We append the 'struct fpu' to the task_struct:
 155  */
 156 static void __init fpu__init_task_struct_size(void)
 157 {
 158         int task_size = sizeof(struct task_struct);
 159
 160         /*
 161          * Subtract off the static size of the register state.
 162          * It potentially has a bunch of padding.
 163          */
 164         task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);
 165
 166         /*
 167          * Add back the dynamically-calculated register state
 168          * size.
 169          */
 170         task_size += fpu_kernel_xstate_size;
 171
 172         /*
 173          * We dynamically size 'struct fpu', so we require that
 174          * it be at the end of 'thread_struct' and that
 175          * 'thread_struct' be at the end of 'task_struct'.  If
 176          * you hit a compile error here, check the structure to
 177          * see if something got added to the end.
 178          */
 179         CHECK_MEMBER_AT_END_OF(struct fpu, state);
 180         CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
 181         CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
 182
 183         arch_task_struct_size = task_size;
 184 }
 185
 186 /*
 187  * Set up the user and kernel xstate sizes based on the legacy FPU context size.
 188  *
 189  * We set this up first, and later it will be overwritten by
 190  * fpu__init_system_xstate() if the CPU knows about xstates.
 191  */
 192 static void __init fpu__init_system_xstate_size_legacy(void)
 193 {
 194         static int on_boot_cpu __initdata = 1;
 195
 196         WARN_ON_FPU(!on_boot_cpu);
 197         on_boot_cpu = 0;
 198
 199         /*
 200          * Note that xstate sizes might be overwritten later during
 201          * fpu__init_system_xstate().
 202          */
 203
 204         if (!boot_cpu_has(X86_FEATURE_FPU)) {
 205                 /*
 206                  * Disable xsave as we do not support it if i387
 207                  * emulation is enabled.
 208                  */
 209                 setup_clear_cpu_cap(X86_FEATURE_XSAVE);
 210                 setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
 211                 fpu_kernel_xstate_size = sizeof(struct swregs_state);
 212         } else {
 213                 if (boot_cpu_has(X86_FEATURE_FXSR))
 214                         fpu_kernel_xstate_size =
 215                                 sizeof(struct fxregs_state);
 216                 else
 217                         fpu_kernel_xstate_size =
 218                                 sizeof(struct fregs_state);
 219         }
 220
 221         fpu_user_xstate_size = fpu_kernel_xstate_size;
 222 }
 223
 224 /*
 225  * Find supported xfeatures based on cpu features and command-line input.
 226  * This must be called after fpu__init_parse_early_param() is called and
 227  * xfeatures_mask is enumerated.
 228  */
 229 u64 __init fpu__get_supported_xfeatures_mask(void)
 230 {
 231         return XCNTXT_MASK;
 232 }
 233
 234 /* Legacy code to initialize eager fpu mode. */
 235 static void __init fpu__init_system_ctx_switch(void)
 236 {
 237         static bool on_boot_cpu __initdata = 1;
 238
 239         WARN_ON_FPU(!on_boot_cpu);
 240         on_boot_cpu = 0;
 241
 242         WARN_ON_FPU(current->thread.fpu.fpstate_active);
 243 }
 244
 245 /*
 246  * We parse fpu parameters early because fpu__init_system() is executed
 247  * before parse_early_param().
 248  */
 249 static void __init fpu__init_parse_early_param(void)
 250 {
 251         if (cmdline_find_option_bool(boot_command_line, "no387"))
 252                 setup_clear_cpu_cap(X86_FEATURE_FPU);
 253
 254         if (cmdline_find_option_bool(boot_command_line, "nofxsr")) {
 255                 setup_clear_cpu_cap(X86_FEATURE_FXSR);
 256                 setup_clear_cpu_cap(X86_FEATURE_FXSR_OPT);
 257                 setup_clear_cpu_cap(X86_FEATURE_XMM);
 258         }
 259
 260         if (cmdline_find_option_bool(boot_command_line, "noxsave"))
 261                 fpu__xstate_clear_all_cpu_caps();
 262
 263         if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
 264                 setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
 265
 266         if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
 267                 setup_clear_cpu_cap(X86_FEATURE_XSAVES);
 268 }
 269
 270 /*
 271  * Called on the boot CPU once per system bootup, to set up the initial
 272  * FPU state that is later cloned into all processes:
 273  */
 274 void __init fpu__init_system(struct cpuinfo_x86 *c)
 275 {
 276         fpu__init_parse_early_param();
 277         fpu__init_system_early_generic(c);
 278
 279         /*
 280          * The FPU has to be operational for some of the
 281          * later FPU init activities:
 282          */
 283         fpu__init_cpu();
 284
 285         fpu__init_system_generic();
 286         fpu__init_system_xstate_size_legacy();
 287         fpu__init_system_xstate();
 288         fpu__init_task_struct_size();
 289
 290         fpu__init_system_ctx_switch();
 291 }