1 // SPDX-License-Identifier: GPL-2.0-only
3 * x86 FPU boot time init code:
5 #include <asm/fpu/internal.h>
6 #include <asm/tlbflush.h>
8 #include <asm/cmdline.h>
10 #include <linux/sched.h>
11 #include <linux/sched/task.h>
12 #include <linux/init.h>
15 * Initialize the registers found in all CPUs, CR0 and CR4:
17 static void fpu__init_cpu_generic(void)
20 unsigned long cr4_mask = 0;
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;
27 cr4_set_bits(cr4_mask);
30 cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
31 if (!boot_cpu_has(X86_FEATURE_FPU))
35 /* Flush out any pending x87 state: */
36 #ifdef CONFIG_MATH_EMULATION
37 if (!boot_cpu_has(X86_FEATURE_FPU))
38 fpstate_init_soft(¤t->thread.fpu.state.soft);
41 asm volatile ("fninit");
45 * Enable all supported FPU features. Called when a CPU is brought online:
47 void fpu__init_cpu(void)
49 fpu__init_cpu_generic();
50 fpu__init_cpu_xstate();
53 static bool fpu__probe_without_cpuid(void)
61 cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
64 asm volatile("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));
66 pr_info("x86/fpu: Probing for FPU: FSW=0x%04hx FCW=0x%04hx\n", fsw, fcw);
68 return fsw == 0 && (fcw & 0x103f) == 0x003f;
71 static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
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);
78 setup_clear_cpu_cap(X86_FEATURE_FPU);
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");
91 * Boot time FPU feature detection code:
93 unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
94 EXPORT_SYMBOL_GPL(mxcsr_feature_mask);
96 static void __init fpu__init_system_mxcsr(void)
98 unsigned int mask = 0;
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;
104 asm volatile("fxsave %0" : "+m" (fxregs));
106 mask = fxregs.mxcsr_mask;
109 * If zero then use the default features mask,
110 * which has all features set, except the
111 * denormals-are-zero feature bit:
116 mxcsr_feature_mask &= mask;
120 * Once per bootup FPU initialization sequences that will run on most x86 CPUs:
122 static void __init fpu__init_system_generic(void)
125 * Set up the legacy init FPU context. (xstate init might overwrite this
126 * with a more modern format, if the CPU supports it.)
128 fpstate_init(&init_fpstate);
130 fpu__init_system_mxcsr();
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:
139 unsigned int fpu_kernel_xstate_size;
140 EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);
142 /* Get alignment of the TYPE. */
143 #define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
146 * Enforce that 'MEMBER' is the last field of 'TYPE'.
148 * Align the computed size with alignment of the TYPE,
149 * because that's how C aligns structs.
151 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
152 BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
156 * We append the 'struct fpu' to the task_struct:
158 static void __init fpu__init_task_struct_size(void)
160 int task_size = sizeof(struct task_struct);
163 * Subtract off the static size of the register state.
164 * It potentially has a bunch of padding.
166 task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);
169 * Add back the dynamically-calculated register state
172 task_size += fpu_kernel_xstate_size;
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.
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);
185 arch_task_struct_size = task_size;
189 * Set up the user and kernel xstate sizes based on the legacy FPU context size.
191 * We set this up first, and later it will be overwritten by
192 * fpu__init_system_xstate() if the CPU knows about xstates.
194 static void __init fpu__init_system_xstate_size_legacy(void)
196 static int on_boot_cpu __initdata = 1;
198 WARN_ON_FPU(!on_boot_cpu);
202 * Note that xstate sizes might be overwritten later during
203 * fpu__init_system_xstate().
206 if (!boot_cpu_has(X86_FEATURE_FPU)) {
207 fpu_kernel_xstate_size = sizeof(struct swregs_state);
209 if (boot_cpu_has(X86_FEATURE_FXSR))
210 fpu_kernel_xstate_size =
211 sizeof(struct fxregs_state);
213 fpu_kernel_xstate_size =
214 sizeof(struct fregs_state);
217 fpu_user_xstate_size = fpu_kernel_xstate_size;
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.
225 u64 __init fpu__get_supported_xfeatures_mask(void)
230 /* Legacy code to initialize eager fpu mode. */
231 static void __init fpu__init_system_ctx_switch(void)
233 static bool on_boot_cpu __initdata = 1;
235 WARN_ON_FPU(!on_boot_cpu);
240 * We parse fpu parameters early because fpu__init_system() is executed
241 * before parse_early_param().
243 static void __init fpu__init_parse_early_param(void)
250 if (cmdline_find_option_bool(boot_command_line, "no387"))
251 #ifdef CONFIG_MATH_EMULATION
252 setup_clear_cpu_cap(X86_FEATURE_FPU);
254 pr_err("Option 'no387' required CONFIG_MATH_EMULATION enabled.\n");
257 if (cmdline_find_option_bool(boot_command_line, "nofxsr"))
258 setup_clear_cpu_cap(X86_FEATURE_FXSR);
261 if (cmdline_find_option_bool(boot_command_line, "noxsave"))
262 setup_clear_cpu_cap(X86_FEATURE_XSAVE);
264 if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
265 setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
267 if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
268 setup_clear_cpu_cap(X86_FEATURE_XSAVES);
270 if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
272 get_option(&argptr, &bit) &&
275 setup_clear_cpu_cap(bit);
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:
282 void __init fpu__init_system(struct cpuinfo_x86 *c)
284 fpu__init_parse_early_param();
285 fpu__init_system_early_generic(c);
288 * The FPU has to be operational for some of the
289 * later FPU init activities:
293 fpu__init_system_generic();
294 fpu__init_system_xstate_size_legacy();
295 fpu__init_system_xstate();
296 fpu__init_task_struct_size();
298 fpu__init_system_ctx_switch();