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 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(¤t->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 __ro_after_init = 0xffffffffu; 93 EXPORT_SYMBOL_GPL(mxcsr_feature_mask); 94 95 static void __init fpu__init_system_mxcsr(void) 96 { 97 unsigned int mask = 0; 98 99 if (boot_cpu_has(X86_FEATURE_FXSR)) { 100 /* Static because GCC does not get 16-byte stack alignment right: */ 101 static struct fxregs_state fxregs __initdata; 102 103 asm volatile("fxsave %0" : "+m" (fxregs)); 104 105 mask = fxregs.mxcsr_mask; 106 107 /* 108 * If zero then use the default features mask, 109 * which has all features set, except the 110 * denormals-are-zero feature bit: 111 */ 112 if (mask == 0) 113 mask = 0x0000ffbf; 114 } 115 mxcsr_feature_mask &= mask; 116 } 117 118 /* 119 * Once per bootup FPU initialization sequences that will run on most x86 CPUs: 120 */ 121 static void __init fpu__init_system_generic(void) 122 { 123 /* 124 * Set up the legacy init FPU context. (xstate init might overwrite this 125 * with a more modern format, if the CPU supports it.) 126 */ 127 fpstate_init(&init_fpstate); 128 129 fpu__init_system_mxcsr(); 130 } 131 132 /* 133 * Size of the FPU context state. All tasks in the system use the 134 * same context size, regardless of what portion they use. 135 * This is inherent to the XSAVE architecture which puts all state 136 * components into a single, continuous memory block: 137 */ 138 unsigned int fpu_kernel_xstate_size __ro_after_init; 139 EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size); 140 141 /* Get alignment of the TYPE. */ 142 #define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test) 143 144 /* 145 * Enforce that 'MEMBER' is the last field of 'TYPE'. 146 * 147 * Align the computed size with alignment of the TYPE, 148 * because that's how C aligns structs. 149 */ 150 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \ 151 BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \ 152 TYPE_ALIGN(TYPE))) 153 154 /* 155 * We append the 'struct fpu' to the task_struct: 156 */ 157 static void __init fpu__init_task_struct_size(void) 158 { 159 int task_size = sizeof(struct task_struct); 160 161 /* 162 * Subtract off the static size of the register state. 163 * It potentially has a bunch of padding. 164 */ 165 task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state); 166 167 /* 168 * Add back the dynamically-calculated register state 169 * size. 170 */ 171 task_size += fpu_kernel_xstate_size; 172 173 /* 174 * We dynamically size 'struct fpu', so we require that 175 * it be at the end of 'thread_struct' and that 176 * 'thread_struct' be at the end of 'task_struct'. If 177 * you hit a compile error here, check the structure to 178 * see if something got added to the end. 179 */ 180 CHECK_MEMBER_AT_END_OF(struct fpu, state); 181 CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu); 182 CHECK_MEMBER_AT_END_OF(struct task_struct, thread); 183 184 arch_task_struct_size = task_size; 185 } 186 187 /* 188 * Set up the user and kernel xstate sizes based on the legacy FPU context size. 189 * 190 * We set this up first, and later it will be overwritten by 191 * fpu__init_system_xstate() if the CPU knows about xstates. 192 */ 193 static void __init fpu__init_system_xstate_size_legacy(void) 194 { 195 static int on_boot_cpu __initdata = 1; 196 197 WARN_ON_FPU(!on_boot_cpu); 198 on_boot_cpu = 0; 199 200 /* 201 * Note that xstate sizes might be overwritten later during 202 * fpu__init_system_xstate(). 203 */ 204 205 if (!boot_cpu_has(X86_FEATURE_FPU)) { 206 fpu_kernel_xstate_size = sizeof(struct swregs_state); 207 } else { 208 if (boot_cpu_has(X86_FEATURE_FXSR)) 209 fpu_kernel_xstate_size = 210 sizeof(struct fxregs_state); 211 else 212 fpu_kernel_xstate_size = 213 sizeof(struct fregs_state); 214 } 215 216 fpu_user_xstate_size = fpu_kernel_xstate_size; 217 } 218 219 /* Legacy code to initialize eager fpu mode. */ 220 static void __init fpu__init_system_ctx_switch(void) 221 { 222 static bool on_boot_cpu __initdata = 1; 223 224 WARN_ON_FPU(!on_boot_cpu); 225 on_boot_cpu = 0; 226 } 227 228 /* 229 * Called on the boot CPU once per system bootup, to set up the initial 230 * FPU state that is later cloned into all processes: 231 */ 232 void __init fpu__init_system(struct cpuinfo_x86 *c) 233 { 234 fpu__init_system_early_generic(c); 235 236 /* 237 * The FPU has to be operational for some of the 238 * later FPU init activities: 239 */ 240 fpu__init_cpu(); 241 242 fpu__init_system_generic(); 243 fpu__init_system_xstate_size_legacy(); 244 fpu__init_system_xstate(); 245 fpu__init_task_struct_size(); 246 247 fpu__init_system_ctx_switch(); 248 } 249