xref: /openbmc/linux/arch/x86/kernel/fpu/init.c (revision d0e22329)
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/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(&current->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 __read_mostly = 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;
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 		/*
207 		 * Disable xsave as we do not support it if i387
208 		 * emulation is enabled.
209 		 */
210 		setup_clear_cpu_cap(X86_FEATURE_XSAVE);
211 		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
212 		fpu_kernel_xstate_size = sizeof(struct swregs_state);
213 	} else {
214 		if (boot_cpu_has(X86_FEATURE_FXSR))
215 			fpu_kernel_xstate_size =
216 				sizeof(struct fxregs_state);
217 		else
218 			fpu_kernel_xstate_size =
219 				sizeof(struct fregs_state);
220 	}
221 
222 	fpu_user_xstate_size = fpu_kernel_xstate_size;
223 }
224 
225 /*
226  * Find supported xfeatures based on cpu features and command-line input.
227  * This must be called after fpu__init_parse_early_param() is called and
228  * xfeatures_mask is enumerated.
229  */
230 u64 __init fpu__get_supported_xfeatures_mask(void)
231 {
232 	return XCNTXT_MASK;
233 }
234 
235 /* Legacy code to initialize eager fpu mode. */
236 static void __init fpu__init_system_ctx_switch(void)
237 {
238 	static bool on_boot_cpu __initdata = 1;
239 
240 	WARN_ON_FPU(!on_boot_cpu);
241 	on_boot_cpu = 0;
242 
243 	WARN_ON_FPU(current->thread.fpu.initialized);
244 }
245 
246 /*
247  * We parse fpu parameters early because fpu__init_system() is executed
248  * before parse_early_param().
249  */
250 static void __init fpu__init_parse_early_param(void)
251 {
252 	char arg[32];
253 	char *argptr = arg;
254 	int bit;
255 
256 	if (cmdline_find_option_bool(boot_command_line, "no387"))
257 		setup_clear_cpu_cap(X86_FEATURE_FPU);
258 
259 	if (cmdline_find_option_bool(boot_command_line, "nofxsr")) {
260 		setup_clear_cpu_cap(X86_FEATURE_FXSR);
261 		setup_clear_cpu_cap(X86_FEATURE_FXSR_OPT);
262 		setup_clear_cpu_cap(X86_FEATURE_XMM);
263 	}
264 
265 	if (cmdline_find_option_bool(boot_command_line, "noxsave"))
266 		fpu__xstate_clear_all_cpu_caps();
267 
268 	if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
269 		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
270 
271 	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
272 		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
273 
274 	if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
275 				sizeof(arg)) &&
276 	    get_option(&argptr, &bit) &&
277 	    bit >= 0 &&
278 	    bit < NCAPINTS * 32)
279 		setup_clear_cpu_cap(bit);
280 }
281 
282 /*
283  * Called on the boot CPU once per system bootup, to set up the initial
284  * FPU state that is later cloned into all processes:
285  */
286 void __init fpu__init_system(struct cpuinfo_x86 *c)
287 {
288 	fpu__init_parse_early_param();
289 	fpu__init_system_early_generic(c);
290 
291 	/*
292 	 * The FPU has to be operational for some of the
293 	 * later FPU init activities:
294 	 */
295 	fpu__init_cpu();
296 
297 	fpu__init_system_generic();
298 	fpu__init_system_xstate_size_legacy();
299 	fpu__init_system_xstate();
300 	fpu__init_task_struct_size();
301 
302 	fpu__init_system_ctx_switch();
303 }
304