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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(&current->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