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/api.h>
   6 #include <asm/tlbflush.h>
   7 #include <asm/setup.h>
   8
   9 #include <linux/sched.h>
  10 #include <linux/sched/task.h>
  11 #include <linux/init.h>
  12
  13 #include "internal.h"
  14 #include "legacy.h"
  15 #include "xstate.h"
  16
  17 /*
  18  * Initialize the registers found in all CPUs, CR0 and CR4:
  19  */
  20 static void fpu__init_cpu_generic(void)
  21 {
  22         unsigned long cr0;
  23         unsigned long cr4_mask = 0;
  24
  25         if (boot_cpu_has(X86_FEATURE_FXSR))
  26                 cr4_mask |= X86_CR4_OSFXSR;
  27         if (boot_cpu_has(X86_FEATURE_XMM))
  28                 cr4_mask |= X86_CR4_OSXMMEXCPT;
  29         if (cr4_mask)
  30                 cr4_set_bits(cr4_mask);
  31
  32         cr0 = read_cr0();
  33         cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
  34         if (!boot_cpu_has(X86_FEATURE_FPU))
  35                 cr0 |= X86_CR0_EM;
  36         write_cr0(cr0);
  37
  38         /* Flush out any pending x87 state: */
  39 #ifdef CONFIG_MATH_EMULATION
  40         if (!boot_cpu_has(X86_FEATURE_FPU))
  41                 fpstate_init_soft(&current->thread.fpu.fpstate->regs.soft);
  42         else
  43 #endif
  44                 asm volatile ("fninit");
  45 }
  46
  47 /*
  48  * Enable all supported FPU features. Called when a CPU is brought online:
  49  */
  50 void fpu__init_cpu(void)
  51 {
  52         fpu__init_cpu_generic();
  53         fpu__init_cpu_xstate();
  54 }
  55
  56 static bool __init fpu__probe_without_cpuid(void)
  57 {
  58         unsigned long cr0;
  59         u16 fsw, fcw;
  60
  61         fsw = fcw = 0xffff;
  62
  63         cr0 = read_cr0();
  64         cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
  65         write_cr0(cr0);
  66
  67         asm volatile("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));
  68
  69         pr_info("x86/fpu: Probing for FPU: FSW=0x%04hx FCW=0x%04hx\n", fsw, fcw);
  70
  71         return fsw == 0 && (fcw & 0x103f) == 0x003f;
  72 }
  73
  74 static void __init fpu__init_system_early_generic(void)
  75 {
  76         if (!boot_cpu_has(X86_FEATURE_CPUID) &&
  77             !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
  78                 if (fpu__probe_without_cpuid())
  79                         setup_force_cpu_cap(X86_FEATURE_FPU);
  80                 else
  81                         setup_clear_cpu_cap(X86_FEATURE_FPU);
  82         }
  83
  84 #ifndef CONFIG_MATH_EMULATION
  85         if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_FPU)) {
  86                 pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
  87                 for (;;)
  88                         asm volatile("hlt");
  89         }
  90 #endif
  91 }
  92
  93 /*
  94  * Boot time FPU feature detection code:
  95  */
  96 unsigned int mxcsr_feature_mask __ro_after_init = 0xffffffffu;
  97 EXPORT_SYMBOL_GPL(mxcsr_feature_mask);
  98
  99 static void __init fpu__init_system_mxcsr(void)
 100 {
 101         unsigned int mask = 0;
 102
 103         if (boot_cpu_has(X86_FEATURE_FXSR)) {
 104                 /* Static because GCC does not get 16-byte stack alignment right: */
 105                 static struct fxregs_state fxregs __initdata;
 106
 107                 asm volatile("fxsave %0" : "+m" (fxregs));
 108
 109                 mask = fxregs.mxcsr_mask;
 110
 111                 /*
 112                  * If zero then use the default features mask,
 113                  * which has all features set, except the
 114                  * denormals-are-zero feature bit:
 115                  */
 116                 if (mask == 0)
 117                         mask = 0x0000ffbf;
 118         }
 119         mxcsr_feature_mask &= mask;
 120 }
 121
 122 /*
 123  * Once per bootup FPU initialization sequences that will run on most x86 CPUs:
 124  */
 125 static void __init fpu__init_system_generic(void)
 126 {
 127         /*
 128          * Set up the legacy init FPU context. Will be updated when the
 129          * CPU supports XSAVE[S].
 130          */
 131         fpstate_init_user(&init_fpstate);
 132
 133         fpu__init_system_mxcsr();
 134 }
 135
 136 /*
 137  * Enforce that 'MEMBER' is the last field of 'TYPE'.
 138  *
 139  * Align the computed size with alignment of the TYPE,
 140  * because that's how C aligns structs.
 141  */
 142 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
 143         BUILD_BUG_ON(sizeof(TYPE) !=         \
 144                      ALIGN(offsetofend(TYPE, MEMBER), _Alignof(TYPE)))
 145
 146 /*
 147  * We append the 'struct fpu' to the task_struct:
 148  */
 149 static void __init fpu__init_task_struct_size(void)
 150 {
 151         int task_size = sizeof(struct task_struct);
 152
 153         /*
 154          * Subtract off the static size of the register state.
 155          * It potentially has a bunch of padding.
 156          */
 157         task_size -= sizeof(current->thread.fpu.__fpstate.regs);
 158
 159         /*
 160          * Add back the dynamically-calculated register state
 161          * size.
 162          */
 163         task_size += fpu_kernel_cfg.default_size;
 164
 165         /*
 166          * We dynamically size 'struct fpu', so we require that
 167          * it be at the end of 'thread_struct' and that
 168          * 'thread_struct' be at the end of 'task_struct'.  If
 169          * you hit a compile error here, check the structure to
 170          * see if something got added to the end.
 171          */
 172         CHECK_MEMBER_AT_END_OF(struct fpu, __fpstate);
 173         CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
 174         CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
 175
 176         arch_task_struct_size = task_size;
 177 }
 178
 179 /*
 180  * Set up the user and kernel xstate sizes based on the legacy FPU context size.
 181  *
 182  * We set this up first, and later it will be overwritten by
 183  * fpu__init_system_xstate() if the CPU knows about xstates.
 184  */
 185 static void __init fpu__init_system_xstate_size_legacy(void)
 186 {
 187         unsigned int size;
 188
 189         /*
 190          * Note that the size configuration might be overwritten later
 191          * during fpu__init_system_xstate().
 192          */
 193         if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
 194                 size = sizeof(struct swregs_state);
 195         } else if (cpu_feature_enabled(X86_FEATURE_FXSR)) {
 196                 size = sizeof(struct fxregs_state);
 197                 fpu_user_cfg.legacy_features = XFEATURE_MASK_FPSSE;
 198         } else {
 199                 size = sizeof(struct fregs_state);
 200                 fpu_user_cfg.legacy_features = XFEATURE_MASK_FP;
 201         }
 202
 203         fpu_kernel_cfg.max_size = size;
 204         fpu_kernel_cfg.default_size = size;
 205         fpu_user_cfg.max_size = size;
 206         fpu_user_cfg.default_size = size;
 207         fpstate_reset(&current->thread.fpu);
 208 }
 209
 210 /*
 211  * Called on the boot CPU once per system bootup, to set up the initial
 212  * FPU state that is later cloned into all processes:
 213  */
 214 void __init fpu__init_system(void)
 215 {
 216         fpstate_reset(&current->thread.fpu);
 217         fpu__init_system_early_generic();
 218
 219         /*
 220          * The FPU has to be operational for some of the
 221          * later FPU init activities:
 222          */
 223         fpu__init_cpu();
 224
 225         fpu__init_system_generic();
 226         fpu__init_system_xstate_size_legacy();
 227         fpu__init_system_xstate(fpu_kernel_cfg.max_size);
 228         fpu__init_task_struct_size();
 229 }