xref: /openbmc/linux/arch/x86/kernel/fpu/init.c (revision 8ab59da2)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * x86 FPU boot time init code:
4  */
5 #include <asm/fpu/api.h>
6 #include <asm/tlbflush.h>
7 #include <asm/setup.h>
8 
9 #include <linux/sched.h>
10 #include <linux/sched/task.h>
11 #include <linux/init.h>
12 
13 #include "internal.h"
14 #include "legacy.h"
15 #include "xstate.h"
16 
17 /*
18  * Initialize the registers found in all CPUs, CR0 and CR4:
19  */
20 static void fpu__init_cpu_generic(void)
21 {
22 	unsigned long cr0;
23 	unsigned long cr4_mask = 0;
24 
25 	if (boot_cpu_has(X86_FEATURE_FXSR))
26 		cr4_mask |= X86_CR4_OSFXSR;
27 	if (boot_cpu_has(X86_FEATURE_XMM))
28 		cr4_mask |= X86_CR4_OSXMMEXCPT;
29 	if (cr4_mask)
30 		cr4_set_bits(cr4_mask);
31 
32 	cr0 = read_cr0();
33 	cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
34 	if (!boot_cpu_has(X86_FEATURE_FPU))
35 		cr0 |= X86_CR0_EM;
36 	write_cr0(cr0);
37 
38 	/* Flush out any pending x87 state: */
39 #ifdef CONFIG_MATH_EMULATION
40 	if (!boot_cpu_has(X86_FEATURE_FPU))
41 		fpstate_init_soft(&current->thread.fpu.fpstate->regs.soft);
42 	else
43 #endif
44 		asm volatile ("fninit");
45 }
46 
47 /*
48  * Enable all supported FPU features. Called when a CPU is brought online:
49  */
50 void fpu__init_cpu(void)
51 {
52 	fpu__init_cpu_generic();
53 	fpu__init_cpu_xstate();
54 }
55 
56 static bool fpu__probe_without_cpuid(void)
57 {
58 	unsigned long cr0;
59 	u16 fsw, fcw;
60 
61 	fsw = fcw = 0xffff;
62 
63 	cr0 = read_cr0();
64 	cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
65 	write_cr0(cr0);
66 
67 	asm volatile("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));
68 
69 	pr_info("x86/fpu: Probing for FPU: FSW=0x%04hx FCW=0x%04hx\n", fsw, fcw);
70 
71 	return fsw == 0 && (fcw & 0x103f) == 0x003f;
72 }
73 
74 static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
75 {
76 	if (!boot_cpu_has(X86_FEATURE_CPUID) &&
77 	    !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
78 		if (fpu__probe_without_cpuid())
79 			setup_force_cpu_cap(X86_FEATURE_FPU);
80 		else
81 			setup_clear_cpu_cap(X86_FEATURE_FPU);
82 	}
83 
84 #ifndef CONFIG_MATH_EMULATION
85 	if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_FPU)) {
86 		pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
87 		for (;;)
88 			asm volatile("hlt");
89 	}
90 #endif
91 }
92 
93 /*
94  * Boot time FPU feature detection code:
95  */
96 unsigned int mxcsr_feature_mask __ro_after_init = 0xffffffffu;
97 EXPORT_SYMBOL_GPL(mxcsr_feature_mask);
98 
99 static void __init fpu__init_system_mxcsr(void)
100 {
101 	unsigned int mask = 0;
102 
103 	if (boot_cpu_has(X86_FEATURE_FXSR)) {
104 		/* Static because GCC does not get 16-byte stack alignment right: */
105 		static struct fxregs_state fxregs __initdata;
106 
107 		asm volatile("fxsave %0" : "+m" (fxregs));
108 
109 		mask = fxregs.mxcsr_mask;
110 
111 		/*
112 		 * If zero then use the default features mask,
113 		 * which has all features set, except the
114 		 * denormals-are-zero feature bit:
115 		 */
116 		if (mask == 0)
117 			mask = 0x0000ffbf;
118 	}
119 	mxcsr_feature_mask &= mask;
120 }
121 
122 /*
123  * Once per bootup FPU initialization sequences that will run on most x86 CPUs:
124  */
125 static void __init fpu__init_system_generic(void)
126 {
127 	/*
128 	 * Set up the legacy init FPU context. Will be updated when the
129 	 * CPU supports XSAVE[S].
130 	 */
131 	fpstate_init_user(&init_fpstate);
132 
133 	fpu__init_system_mxcsr();
134 }
135 
136 /* Get alignment of the TYPE. */
137 #define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
138 
139 /*
140  * Enforce that 'MEMBER' is the last field of 'TYPE'.
141  *
142  * Align the computed size with alignment of the TYPE,
143  * because that's how C aligns structs.
144  */
145 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
146 	BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
147 					   TYPE_ALIGN(TYPE)))
148 
149 /*
150  * We append the 'struct fpu' to the task_struct:
151  */
152 static void __init fpu__init_task_struct_size(void)
153 {
154 	int task_size = sizeof(struct task_struct);
155 
156 	/*
157 	 * Subtract off the static size of the register state.
158 	 * It potentially has a bunch of padding.
159 	 */
160 	task_size -= sizeof(current->thread.fpu.__fpstate.regs);
161 
162 	/*
163 	 * Add back the dynamically-calculated register state
164 	 * size.
165 	 */
166 	task_size += fpu_kernel_cfg.default_size;
167 
168 	/*
169 	 * We dynamically size 'struct fpu', so we require that
170 	 * it be at the end of 'thread_struct' and that
171 	 * 'thread_struct' be at the end of 'task_struct'.  If
172 	 * you hit a compile error here, check the structure to
173 	 * see if something got added to the end.
174 	 */
175 	CHECK_MEMBER_AT_END_OF(struct fpu, __fpstate);
176 	CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
177 	CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
178 
179 	arch_task_struct_size = task_size;
180 }
181 
182 /*
183  * Set up the user and kernel xstate sizes based on the legacy FPU context size.
184  *
185  * We set this up first, and later it will be overwritten by
186  * fpu__init_system_xstate() if the CPU knows about xstates.
187  */
188 static void __init fpu__init_system_xstate_size_legacy(void)
189 {
190 	unsigned int size;
191 
192 	/*
193 	 * Note that the size configuration might be overwritten later
194 	 * during fpu__init_system_xstate().
195 	 */
196 	if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
197 		size = sizeof(struct swregs_state);
198 	} else if (cpu_feature_enabled(X86_FEATURE_FXSR)) {
199 		size = sizeof(struct fxregs_state);
200 		fpu_user_cfg.legacy_features = XFEATURE_MASK_FPSSE;
201 	} else {
202 		size = sizeof(struct fregs_state);
203 		fpu_user_cfg.legacy_features = XFEATURE_MASK_FP;
204 	}
205 
206 	fpu_kernel_cfg.max_size = size;
207 	fpu_kernel_cfg.default_size = size;
208 	fpu_user_cfg.max_size = size;
209 	fpu_user_cfg.default_size = size;
210 	fpstate_reset(&current->thread.fpu);
211 }
212 
213 /*
214  * Called on the boot CPU once per system bootup, to set up the initial
215  * FPU state that is later cloned into all processes:
216  */
217 void __init fpu__init_system(struct cpuinfo_x86 *c)
218 {
219 	fpstate_reset(&current->thread.fpu);
220 	fpu__init_system_early_generic(c);
221 
222 	/*
223 	 * The FPU has to be operational for some of the
224 	 * later FPU init activities:
225 	 */
226 	fpu__init_cpu();
227 
228 	fpu__init_system_generic();
229 	fpu__init_system_xstate_size_legacy();
230 	fpu__init_system_xstate(fpu_kernel_cfg.max_size);
231 	fpu__init_task_struct_size();
232 }
233