arch/x86/kernel/fpu/init.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * x86 FPU boot time init code:
   4  */
   5 #include <asm/fpu/internal.h>
   6 #include <asm/tlbflush.h>
   7 #include <asm/setup.h>
   8 #include <asm/cmdline.h>
   9
  10 #include <linux/sched.h>
  11 #include <linux/sched/task.h>
  12 #include <linux/init.h>
  13
  14 /*
  15  * Initialize the registers found in all CPUs, CR0 and CR4:
  16  */
  17 static void fpu__init_cpu_generic(void)
  18 {
  19         unsigned long cr0;
  20         unsigned long cr4_mask = 0;
  21
  22         if (boot_cpu_has(X86_FEATURE_FXSR))
  23                 cr4_mask |= X86_CR4_OSFXSR;
  24         if (boot_cpu_has(X86_FEATURE_XMM))
  25                 cr4_mask |= X86_CR4_OSXMMEXCPT;
  26         if (cr4_mask)
  27                 cr4_set_bits(cr4_mask);
  28
  29         cr0 = read_cr0();
  30         cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
  31         if (!boot_cpu_has(X86_FEATURE_FPU))
  32                 cr0 |= X86_CR0_EM;
  33         write_cr0(cr0);
  34
  35         /* Flush out any pending x87 state: */
  36 #ifdef CONFIG_MATH_EMULATION
  37         if (!boot_cpu_has(X86_FEATURE_FPU))
  38                 fpstate_init_soft(&current->thread.fpu.state.soft);
  39         else
  40 #endif
  41                 asm volatile ("fninit");
  42 }
  43
  44 /*
  45  * Enable all supported FPU features. Called when a CPU is brought online:
  46  */
  47 void fpu__init_cpu(void)
  48 {
  49         fpu__init_cpu_generic();
  50         fpu__init_cpu_xstate();
  51 }
  52
  53 static bool fpu__probe_without_cpuid(void)
  54 {
  55         unsigned long cr0;
  56         u16 fsw, fcw;
  57
  58         fsw = fcw = 0xffff;
  59
  60         cr0 = read_cr0();
  61         cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
  62         write_cr0(cr0);
  63
  64         asm volatile("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));
  65
  66         pr_info("x86/fpu: Probing for FPU: FSW=0x%04hx FCW=0x%04hx\n", fsw, fcw);
  67
  68         return fsw == 0 && (fcw & 0x103f) == 0x003f;
  69 }
  70
  71 static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
  72 {
  73         if (!boot_cpu_has(X86_FEATURE_CPUID) &&
  74             !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
  75                 if (fpu__probe_without_cpuid())
  76                         setup_force_cpu_cap(X86_FEATURE_FPU);
  77                 else
  78                         setup_clear_cpu_cap(X86_FEATURE_FPU);
  79         }
  80
  81 #ifndef CONFIG_MATH_EMULATION
  82         if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_FPU)) {
  83                 pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
  84                 for (;;)
  85                         asm volatile("hlt");
  86         }
  87 #endif
  88 }
  89
  90 /*
  91  * Boot time FPU feature detection code:
  92  */
  93 unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
  94 EXPORT_SYMBOL_GPL(mxcsr_feature_mask);
  95
  96 static void __init fpu__init_system_mxcsr(void)
  97 {
  98         unsigned int mask = 0;
  99
 100         if (boot_cpu_has(X86_FEATURE_FXSR)) {
 101                 /* Static because GCC does not get 16-byte stack alignment right: */
 102                 static struct fxregs_state fxregs __initdata;
 103
 104                 asm volatile("fxsave %0" : "+m" (fxregs));
 105
 106                 mask = fxregs.mxcsr_mask;
 107
 108                 /*
 109                  * If zero then use the default features mask,
 110                  * which has all features set, except the
 111                  * denormals-are-zero feature bit:
 112                  */
 113                 if (mask == 0)
 114                         mask = 0x0000ffbf;
 115         }
 116         mxcsr_feature_mask &= mask;
 117 }
 118
 119 /*
 120  * Once per bootup FPU initialization sequences that will run on most x86 CPUs:
 121  */
 122 static void __init fpu__init_system_generic(void)
 123 {
 124         /*
 125          * Set up the legacy init FPU context. (xstate init might overwrite this
 126          * with a more modern format, if the CPU supports it.)
 127          */
 128         fpstate_init(&init_fpstate);
 129
 130         fpu__init_system_mxcsr();
 131 }
 132
 133 /*
 134  * Size of the FPU context state. All tasks in the system use the
 135  * same context size, regardless of what portion they use.
 136  * This is inherent to the XSAVE architecture which puts all state
 137  * components into a single, continuous memory block:
 138  */
 139 unsigned int fpu_kernel_xstate_size;
 140 EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);
 141
 142 /* Get alignment of the TYPE. */
 143 #define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
 144
 145 /*
 146  * Enforce that 'MEMBER' is the last field of 'TYPE'.
 147  *
 148  * Align the computed size with alignment of the TYPE,
 149  * because that's how C aligns structs.
 150  */
 151 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
 152         BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
 153                                            TYPE_ALIGN(TYPE)))
 154
 155 /*
 156  * We append the 'struct fpu' to the task_struct:
 157  */
 158 static void __init fpu__init_task_struct_size(void)
 159 {
 160         int task_size = sizeof(struct task_struct);
 161
 162         /*
 163          * Subtract off the static size of the register state.
 164          * It potentially has a bunch of padding.
 165          */
 166         task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);
 167
 168         /*
 169          * Add back the dynamically-calculated register state
 170          * size.
 171          */
 172         task_size += fpu_kernel_xstate_size;
 173
 174         /*
 175          * We dynamically size 'struct fpu', so we require that
 176          * it be at the end of 'thread_struct' and that
 177          * 'thread_struct' be at the end of 'task_struct'.  If
 178          * you hit a compile error here, check the structure to
 179          * see if something got added to the end.
 180          */
 181         CHECK_MEMBER_AT_END_OF(struct fpu, state);
 182         CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
 183         CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
 184
 185         arch_task_struct_size = task_size;
 186 }
 187
 188 /*
 189  * Set up the user and kernel xstate sizes based on the legacy FPU context size.
 190  *
 191  * We set this up first, and later it will be overwritten by
 192  * fpu__init_system_xstate() if the CPU knows about xstates.
 193  */
 194 static void __init fpu__init_system_xstate_size_legacy(void)
 195 {
 196         static int on_boot_cpu __initdata = 1;
 197
 198         WARN_ON_FPU(!on_boot_cpu);
 199         on_boot_cpu = 0;
 200
 201         /*
 202          * Note that xstate sizes might be overwritten later during
 203          * fpu__init_system_xstate().
 204          */
 205
 206         if (!boot_cpu_has(X86_FEATURE_FPU)) {
 207                 fpu_kernel_xstate_size = sizeof(struct swregs_state);
 208         } else {
 209                 if (boot_cpu_has(X86_FEATURE_FXSR))
 210                         fpu_kernel_xstate_size =
 211                                 sizeof(struct fxregs_state);
 212                 else
 213                         fpu_kernel_xstate_size =
 214                                 sizeof(struct fregs_state);
 215         }
 216
 217         fpu_user_xstate_size = fpu_kernel_xstate_size;
 218 }
 219
 220 /*
 221  * Find supported xfeatures based on cpu features and command-line input.
 222  * This must be called after fpu__init_parse_early_param() is called and
 223  * xfeatures_mask is enumerated.
 224  */
 225 u64 __init fpu__get_supported_xfeatures_mask(void)
 226 {
 227         return XCNTXT_MASK;
 228 }
 229
 230 /* Legacy code to initialize eager fpu mode. */
 231 static void __init fpu__init_system_ctx_switch(void)
 232 {
 233         static bool on_boot_cpu __initdata = 1;
 234
 235         WARN_ON_FPU(!on_boot_cpu);
 236         on_boot_cpu = 0;
 237 }
 238
 239 /*
 240  * We parse fpu parameters early because fpu__init_system() is executed
 241  * before parse_early_param().
 242  */
 243 static void __init fpu__init_parse_early_param(void)
 244 {
 245         char arg[32];
 246         char *argptr = arg;
 247         int bit;
 248
 249 #ifdef CONFIG_X86_32
 250         if (cmdline_find_option_bool(boot_command_line, "no387"))
 251 #ifdef CONFIG_MATH_EMULATION
 252                 setup_clear_cpu_cap(X86_FEATURE_FPU);
 253 #else
 254                 pr_err("Option 'no387' required CONFIG_MATH_EMULATION enabled.\n");
 255 #endif
 256
 257         if (cmdline_find_option_bool(boot_command_line, "nofxsr"))
 258                 setup_clear_cpu_cap(X86_FEATURE_FXSR);
 259 #endif
 260
 261         if (cmdline_find_option_bool(boot_command_line, "noxsave"))
 262                 setup_clear_cpu_cap(X86_FEATURE_XSAVE);
 263
 264         if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
 265                 setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
 266
 267         if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
 268                 setup_clear_cpu_cap(X86_FEATURE_XSAVES);
 269
 270         if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
 271                                 sizeof(arg)) &&
 272             get_option(&argptr, &bit) &&
 273             bit >= 0 &&
 274             bit < NCAPINTS * 32)
 275                 setup_clear_cpu_cap(bit);
 276 }
 277
 278 /*
 279  * Called on the boot CPU once per system bootup, to set up the initial
 280  * FPU state that is later cloned into all processes:
 281  */
 282 void __init fpu__init_system(struct cpuinfo_x86 *c)
 283 {
 284         fpu__init_parse_early_param();
 285         fpu__init_system_early_generic(c);
 286
 287         /*
 288          * The FPU has to be operational for some of the
 289          * later FPU init activities:
 290          */
 291         fpu__init_cpu();
 292
 293         fpu__init_system_generic();
 294         fpu__init_system_xstate_size_legacy();
 295         fpu__init_system_xstate();
 296         fpu__init_task_struct_size();
 297
 298         fpu__init_system_ctx_switch();
 299 }