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 */
fpu__init_cpu_generic(void)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(¤t->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 */
fpu__init_cpu(void)47 void fpu__init_cpu(void)
48 {
49 fpu__init_cpu_generic();
50 fpu__init_cpu_xstate();
51 }
52
fpu__probe_without_cpuid(void)53 static bool __init 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
fpu__init_system_early_generic(void)71 static void __init fpu__init_system_early_generic(void)
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
fpu__init_system_mxcsr(void)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 */
fpu__init_system_generic(void)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 /*
143 * Enforce that 'MEMBER' is the last field of 'TYPE'.
144 *
145 * Align the computed size with alignment of the TYPE,
146 * because that's how C aligns structs.
147 */
148 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
149 BUILD_BUG_ON(sizeof(TYPE) != \
150 ALIGN(offsetofend(TYPE, MEMBER), _Alignof(TYPE)))
151
152 /*
153 * We append the 'struct fpu' to the task_struct:
154 */
fpu__init_task_struct_size(void)155 static void __init fpu__init_task_struct_size(void)
156 {
157 int task_size = sizeof(struct task_struct);
158
159 /*
160 * Subtract off the static size of the register state.
161 * It potentially has a bunch of padding.
162 */
163 task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);
164
165 /*
166 * Add back the dynamically-calculated register state
167 * size.
168 */
169 task_size += fpu_kernel_xstate_size;
170
171 /*
172 * We dynamically size 'struct fpu', so we require that
173 * it be at the end of 'thread_struct' and that
174 * 'thread_struct' be at the end of 'task_struct'. If
175 * you hit a compile error here, check the structure to
176 * see if something got added to the end.
177 */
178 CHECK_MEMBER_AT_END_OF(struct fpu, state);
179 CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
180 CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
181
182 arch_task_struct_size = task_size;
183 }
184
185 /*
186 * Set up the user and kernel xstate sizes based on the legacy FPU context size.
187 *
188 * We set this up first, and later it will be overwritten by
189 * fpu__init_system_xstate() if the CPU knows about xstates.
190 */
fpu__init_system_xstate_size_legacy(void)191 static void __init fpu__init_system_xstate_size_legacy(void)
192 {
193 static int on_boot_cpu __initdata = 1;
194
195 WARN_ON_FPU(!on_boot_cpu);
196 on_boot_cpu = 0;
197
198 /*
199 * Note that xstate sizes might be overwritten later during
200 * fpu__init_system_xstate().
201 */
202
203 if (!boot_cpu_has(X86_FEATURE_FPU)) {
204 fpu_kernel_xstate_size = sizeof(struct swregs_state);
205 } else {
206 if (boot_cpu_has(X86_FEATURE_FXSR))
207 fpu_kernel_xstate_size =
208 sizeof(struct fxregs_state);
209 else
210 fpu_kernel_xstate_size =
211 sizeof(struct fregs_state);
212 }
213
214 fpu_user_xstate_size = fpu_kernel_xstate_size;
215 }
216
217 /*
218 * Find supported xfeatures based on cpu features and command-line input.
219 * This must be called after fpu__init_parse_early_param() is called and
220 * xfeatures_mask is enumerated.
221 */
fpu__get_supported_xfeatures_mask(void)222 u64 __init fpu__get_supported_xfeatures_mask(void)
223 {
224 return XCNTXT_MASK;
225 }
226
227 /* Legacy code to initialize eager fpu mode. */
fpu__init_system_ctx_switch(void)228 static void __init fpu__init_system_ctx_switch(void)
229 {
230 static bool on_boot_cpu __initdata = 1;
231
232 WARN_ON_FPU(!on_boot_cpu);
233 on_boot_cpu = 0;
234 }
235
236 /*
237 * We parse fpu parameters early because fpu__init_system() is executed
238 * before parse_early_param().
239 */
fpu__init_parse_early_param(void)240 static void __init fpu__init_parse_early_param(void)
241 {
242 char arg[128];
243 char *argptr = arg;
244 int arglen, res, bit;
245
246 #ifdef CONFIG_X86_32
247 if (cmdline_find_option_bool(boot_command_line, "no387"))
248 #ifdef CONFIG_MATH_EMULATION
249 setup_clear_cpu_cap(X86_FEATURE_FPU);
250 #else
251 pr_err("Option 'no387' required CONFIG_MATH_EMULATION enabled.\n");
252 #endif
253
254 if (cmdline_find_option_bool(boot_command_line, "nofxsr"))
255 setup_clear_cpu_cap(X86_FEATURE_FXSR);
256 #endif
257
258 if (cmdline_find_option_bool(boot_command_line, "noxsave"))
259 setup_clear_cpu_cap(X86_FEATURE_XSAVE);
260
261 if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
262 setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
263
264 if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
265 setup_clear_cpu_cap(X86_FEATURE_XSAVES);
266
267 arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
268 if (arglen <= 0)
269 return;
270
271 pr_info("Clearing CPUID bits:");
272 do {
273 res = get_option(&argptr, &bit);
274 if (res == 0 || res == 3)
275 break;
276
277 /* If the argument was too long, the last bit may be cut off */
278 if (res == 1 && arglen >= sizeof(arg))
279 break;
280
281 if (bit >= 0 && bit < NCAPINTS * 32) {
282 pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
283 setup_clear_cpu_cap(bit);
284 }
285 } while (res == 2);
286 pr_cont("\n");
287 }
288
289 /*
290 * Called on the boot CPU once per system bootup, to set up the initial
291 * FPU state that is later cloned into all processes:
292 */
fpu__init_system(void)293 void __init fpu__init_system(void)
294 {
295 fpu__init_parse_early_param();
296 fpu__init_system_early_generic();
297
298 /*
299 * The FPU has to be operational for some of the
300 * later FPU init activities:
301 */
302 fpu__init_cpu();
303
304 fpu__init_system_generic();
305 fpu__init_system_xstate_size_legacy();
306 fpu__init_system_xstate();
307 fpu__init_task_struct_size();
308
309 fpu__init_system_ctx_switch();
310 }
311