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(¤t->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 __init 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 __init fpu__init_system_early_generic(void)
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 /*
137 * Enforce that 'MEMBER' is the last field of 'TYPE'.
138 *
139 * Align the computed size with alignment of the TYPE,
140 * because that's how C aligns structs.
141 */
142 #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
143 BUILD_BUG_ON(sizeof(TYPE) != \
144 ALIGN(offsetofend(TYPE, MEMBER), _Alignof(TYPE)))
145
146 /*
147 * We append the 'struct fpu' to the task_struct:
148 */
149 static void __init fpu__init_task_struct_size(void)
150 {
151 int task_size = sizeof(struct task_struct);
152
153 /*
154 * Subtract off the static size of the register state.
155 * It potentially has a bunch of padding.
156 */
157 task_size -= sizeof(current->thread.fpu.__fpstate.regs);
158
159 /*
160 * Add back the dynamically-calculated register state
161 * size.
162 */
163 task_size += fpu_kernel_cfg.default_size;
164
165 /*
166 * We dynamically size 'struct fpu', so we require that
167 * it be at the end of 'thread_struct' and that
168 * 'thread_struct' be at the end of 'task_struct'. If
169 * you hit a compile error here, check the structure to
170 * see if something got added to the end.
171 */
172 CHECK_MEMBER_AT_END_OF(struct fpu, __fpstate);
173 CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
174 CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
175
176 arch_task_struct_size = task_size;
177 }
178
179 /*
180 * Set up the user and kernel xstate sizes based on the legacy FPU context size.
181 *
182 * We set this up first, and later it will be overwritten by
183 * fpu__init_system_xstate() if the CPU knows about xstates.
184 */
185 static void __init fpu__init_system_xstate_size_legacy(void)
186 {
187 unsigned int size;
188
189 /*
190 * Note that the size configuration might be overwritten later
191 * during fpu__init_system_xstate().
192 */
193 if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
194 size = sizeof(struct swregs_state);
195 } else if (cpu_feature_enabled(X86_FEATURE_FXSR)) {
196 size = sizeof(struct fxregs_state);
197 fpu_user_cfg.legacy_features = XFEATURE_MASK_FPSSE;
198 } else {
199 size = sizeof(struct fregs_state);
200 fpu_user_cfg.legacy_features = XFEATURE_MASK_FP;
201 }
202
203 fpu_kernel_cfg.max_size = size;
204 fpu_kernel_cfg.default_size = size;
205 fpu_user_cfg.max_size = size;
206 fpu_user_cfg.default_size = size;
207 fpstate_reset(¤t->thread.fpu);
208 }
209
210 /*
211 * Called on the boot CPU once per system bootup, to set up the initial
212 * FPU state that is later cloned into all processes:
213 */
214 void __init fpu__init_system(void)
215 {
216 fpstate_reset(¤t->thread.fpu);
217 fpu__init_system_early_generic();
218
219 /*
220 * The FPU has to be operational for some of the
221 * later FPU init activities:
222 */
223 fpu__init_cpu();
224
225 fpu__init_system_generic();
226 fpu__init_system_xstate_size_legacy();
227 fpu__init_system_xstate(fpu_kernel_cfg.max_size);
228 fpu__init_task_struct_size();
229 }
230
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