xref: /openbmc/linux/arch/x86/kernel/fpu/init.c (revision ae3473231e77a3f1909d48cd144cebe5e1d049b3)
1 /*
2  * x86 FPU boot time init code:
3  */
4 #include <asm/fpu/internal.h>
5 #include <asm/tlbflush.h>
6 #include <asm/setup.h>
7 #include <asm/cmdline.h>
8 
9 #include <linux/sched.h>
10 #include <linux/init.h>
11 
12 /*
13  * Initialize the registers found in all CPUs, CR0 and CR4:
14  */
15 static void fpu__init_cpu_generic(void)
16 {
17 	unsigned long cr0;
18 	unsigned long cr4_mask = 0;
19 
20 	if (boot_cpu_has(X86_FEATURE_FXSR))
21 		cr4_mask |= X86_CR4_OSFXSR;
22 	if (boot_cpu_has(X86_FEATURE_XMM))
23 		cr4_mask |= X86_CR4_OSXMMEXCPT;
24 	if (cr4_mask)
25 		cr4_set_bits(cr4_mask);
26 
27 	cr0 = read_cr0();
28 	cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
29 	if (!boot_cpu_has(X86_FEATURE_FPU))
30 		cr0 |= X86_CR0_EM;
31 	write_cr0(cr0);
32 
33 	/* Flush out any pending x87 state: */
34 #ifdef CONFIG_MATH_EMULATION
35 	if (!boot_cpu_has(X86_FEATURE_FPU))
36 		fpstate_init_soft(&current->thread.fpu.state.soft);
37 	else
38 #endif
39 		asm volatile ("fninit");
40 }
41 
42 /*
43  * Enable all supported FPU features. Called when a CPU is brought online:
44  */
45 void fpu__init_cpu(void)
46 {
47 	fpu__init_cpu_generic();
48 	fpu__init_cpu_xstate();
49 }
50 
51 /*
52  * The earliest FPU detection code.
53  *
54  * Set the X86_FEATURE_FPU CPU-capability bit based on
55  * trying to execute an actual sequence of FPU instructions:
56  */
57 static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
58 {
59 	unsigned long cr0;
60 	u16 fsw, fcw;
61 
62 	fsw = fcw = 0xffff;
63 
64 	cr0 = read_cr0();
65 	cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
66 	write_cr0(cr0);
67 
68 	if (!test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
69 		asm volatile("fninit ; fnstsw %0 ; fnstcw %1"
70 			     : "+m" (fsw), "+m" (fcw));
71 
72 		if (fsw == 0 && (fcw & 0x103f) == 0x003f)
73 			set_cpu_cap(c, X86_FEATURE_FPU);
74 		else
75 			clear_cpu_cap(c, X86_FEATURE_FPU);
76 	}
77 
78 #ifndef CONFIG_MATH_EMULATION
79 	if (!boot_cpu_has(X86_FEATURE_FPU)) {
80 		pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
81 		for (;;)
82 			asm volatile("hlt");
83 	}
84 #endif
85 }
86 
87 /*
88  * Boot time FPU feature detection code:
89  */
90 unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
91 
92 static void __init fpu__init_system_mxcsr(void)
93 {
94 	unsigned int mask = 0;
95 
96 	if (boot_cpu_has(X86_FEATURE_FXSR)) {
97 		/* Static because GCC does not get 16-byte stack alignment right: */
98 		static struct fxregs_state fxregs __initdata;
99 
100 		asm volatile("fxsave %0" : "+m" (fxregs));
101 
102 		mask = fxregs.mxcsr_mask;
103 
104 		/*
105 		 * If zero then use the default features mask,
106 		 * which has all features set, except the
107 		 * denormals-are-zero feature bit:
108 		 */
109 		if (mask == 0)
110 			mask = 0x0000ffbf;
111 	}
112 	mxcsr_feature_mask &= mask;
113 }
114 
115 /*
116  * Once per bootup FPU initialization sequences that will run on most x86 CPUs:
117  */
118 static void __init fpu__init_system_generic(void)
119 {
120 	/*
121 	 * Set up the legacy init FPU context. (xstate init might overwrite this
122 	 * with a more modern format, if the CPU supports it.)
123 	 */
124 	fpstate_init(&init_fpstate);
125 
126 	fpu__init_system_mxcsr();
127 }
128 
129 /*
130  * Size of the FPU context state. All tasks in the system use the
131  * same context size, regardless of what portion they use.
132  * This is inherent to the XSAVE architecture which puts all state
133  * components into a single, continuous memory block:
134  */
135 unsigned int fpu_kernel_xstate_size;
136 EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);
137 
138 /* Get alignment of the TYPE. */
139 #define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
140 
141 /*
142  * Enforce that 'MEMBER' is the last field of 'TYPE'.
143  *
144  * Align the computed size with alignment of the TYPE,
145  * because that's how C aligns structs.
146  */
147 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
148 	BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
149 					   TYPE_ALIGN(TYPE)))
150 
151 /*
152  * We append the 'struct fpu' to the task_struct:
153  */
154 static void __init fpu__init_task_struct_size(void)
155 {
156 	int task_size = sizeof(struct task_struct);
157 
158 	/*
159 	 * Subtract off the static size of the register state.
160 	 * It potentially has a bunch of padding.
161 	 */
162 	task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);
163 
164 	/*
165 	 * Add back the dynamically-calculated register state
166 	 * size.
167 	 */
168 	task_size += fpu_kernel_xstate_size;
169 
170 	/*
171 	 * We dynamically size 'struct fpu', so we require that
172 	 * it be at the end of 'thread_struct' and that
173 	 * 'thread_struct' be at the end of 'task_struct'.  If
174 	 * you hit a compile error here, check the structure to
175 	 * see if something got added to the end.
176 	 */
177 	CHECK_MEMBER_AT_END_OF(struct fpu, state);
178 	CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
179 	CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
180 
181 	arch_task_struct_size = task_size;
182 }
183 
184 /*
185  * Set up the user and kernel xstate sizes based on the legacy FPU context size.
186  *
187  * We set this up first, and later it will be overwritten by
188  * fpu__init_system_xstate() if the CPU knows about xstates.
189  */
190 static void __init fpu__init_system_xstate_size_legacy(void)
191 {
192 	static int on_boot_cpu __initdata = 1;
193 
194 	WARN_ON_FPU(!on_boot_cpu);
195 	on_boot_cpu = 0;
196 
197 	/*
198 	 * Note that xstate sizes might be overwritten later during
199 	 * fpu__init_system_xstate().
200 	 */
201 
202 	if (!boot_cpu_has(X86_FEATURE_FPU)) {
203 		/*
204 		 * Disable xsave as we do not support it if i387
205 		 * emulation is enabled.
206 		 */
207 		setup_clear_cpu_cap(X86_FEATURE_XSAVE);
208 		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
209 		fpu_kernel_xstate_size = sizeof(struct swregs_state);
210 	} else {
211 		if (boot_cpu_has(X86_FEATURE_FXSR))
212 			fpu_kernel_xstate_size =
213 				sizeof(struct fxregs_state);
214 		else
215 			fpu_kernel_xstate_size =
216 				sizeof(struct fregs_state);
217 	}
218 
219 	fpu_user_xstate_size = fpu_kernel_xstate_size;
220 }
221 
222 /*
223  * Find supported xfeatures based on cpu features and command-line input.
224  * This must be called after fpu__init_parse_early_param() is called and
225  * xfeatures_mask is enumerated.
226  */
227 u64 __init fpu__get_supported_xfeatures_mask(void)
228 {
229 	return XCNTXT_MASK;
230 }
231 
232 /* Legacy code to initialize eager fpu mode. */
233 static void __init fpu__init_system_ctx_switch(void)
234 {
235 	static bool on_boot_cpu __initdata = 1;
236 
237 	WARN_ON_FPU(!on_boot_cpu);
238 	on_boot_cpu = 0;
239 
240 	WARN_ON_FPU(current->thread.fpu.fpstate_active);
241 }
242 
243 /*
244  * We parse fpu parameters early because fpu__init_system() is executed
245  * before parse_early_param().
246  */
247 static void __init fpu__init_parse_early_param(void)
248 {
249 	if (cmdline_find_option_bool(boot_command_line, "no387"))
250 		setup_clear_cpu_cap(X86_FEATURE_FPU);
251 
252 	if (cmdline_find_option_bool(boot_command_line, "nofxsr")) {
253 		setup_clear_cpu_cap(X86_FEATURE_FXSR);
254 		setup_clear_cpu_cap(X86_FEATURE_FXSR_OPT);
255 		setup_clear_cpu_cap(X86_FEATURE_XMM);
256 	}
257 
258 	if (cmdline_find_option_bool(boot_command_line, "noxsave"))
259 		fpu__xstate_clear_all_cpu_caps();
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 
268 /*
269  * Called on the boot CPU once per system bootup, to set up the initial
270  * FPU state that is later cloned into all processes:
271  */
272 void __init fpu__init_system(struct cpuinfo_x86 *c)
273 {
274 	fpu__init_parse_early_param();
275 	fpu__init_system_early_generic(c);
276 
277 	/*
278 	 * The FPU has to be operational for some of the
279 	 * later FPU init activities:
280 	 */
281 	fpu__init_cpu();
282 
283 	fpu__init_system_generic();
284 	fpu__init_system_xstate_size_legacy();
285 	fpu__init_system_xstate();
286 	fpu__init_task_struct_size();
287 
288 	fpu__init_system_ctx_switch();
289 }
290