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(¤t->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 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 fpu__init_system_early_generic(struct cpuinfo_x86 *c) 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(¤t->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(struct cpuinfo_x86 *c) 215 { 216 fpstate_reset(¤t->thread.fpu); 217 fpu__init_system_early_generic(c); 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 } 230