summaryrefslogtreecommitdiff
path: root/arch/x86/kernel/fpu/init.c
blob: 20d8fa7124c77a7ea08a185c40c5b0758f6b9300 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
/*
 * x86 FPU boot time init code:
 */
#include <asm/fpu/internal.h>
#include <asm/tlbflush.h>
#include <asm/setup.h>
#include <asm/cmdline.h>

#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/init.h>

/*
 * Initialize the registers found in all CPUs, CR0 and CR4:
 */
static void fpu__init_cpu_generic(void)
{
	unsigned long cr0;
	unsigned long cr4_mask = 0;

	if (boot_cpu_has(X86_FEATURE_FXSR))
		cr4_mask |= X86_CR4_OSFXSR;
	if (boot_cpu_has(X86_FEATURE_XMM))
		cr4_mask |= X86_CR4_OSXMMEXCPT;
	if (cr4_mask)
		cr4_set_bits(cr4_mask);

	cr0 = read_cr0();
	cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
	if (!boot_cpu_has(X86_FEATURE_FPU))
		cr0 |= X86_CR0_EM;
	write_cr0(cr0);

	/* Flush out any pending x87 state: */
#ifdef CONFIG_MATH_EMULATION
	if (!boot_cpu_has(X86_FEATURE_FPU))
		fpstate_init_soft(&current->thread.fpu.state.soft);
	else
#endif
		asm volatile ("fninit");
}

/*
 * Enable all supported FPU features. Called when a CPU is brought online:
 */
void fpu__init_cpu(void)
{
	fpu__init_cpu_generic();
	fpu__init_cpu_xstate();
}

static bool fpu__probe_without_cpuid(void)
{
	unsigned long cr0;
	u16 fsw, fcw;

	fsw = fcw = 0xffff;

	cr0 = read_cr0();
	cr0 &= ~(X86_CR0_TS | X86_CR0_EM);
	write_cr0(cr0);

	asm volatile("fninit ; fnstsw %0 ; fnstcw %1" : "+m" (fsw), "+m" (fcw));

	pr_info("x86/fpu: Probing for FPU: FSW=0x%04hx FCW=0x%04hx\n", fsw, fcw);

	return fsw == 0 && (fcw & 0x103f) == 0x003f;
}

static void fpu__init_system_early_generic(struct cpuinfo_x86 *c)
{
	if (!boot_cpu_has(X86_FEATURE_CPUID) &&
	    !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
		if (fpu__probe_without_cpuid())
			setup_force_cpu_cap(X86_FEATURE_FPU);
		else
			setup_clear_cpu_cap(X86_FEATURE_FPU);
	}

#ifndef CONFIG_MATH_EMULATION
	if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_FPU)) {
		pr_emerg("x86/fpu: Giving up, no FPU found and no math emulation present\n");
		for (;;)
			asm volatile("hlt");
	}
#endif
}

/*
 * Boot time FPU feature detection code:
 */
unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
EXPORT_SYMBOL_GPL(mxcsr_feature_mask);

static void __init fpu__init_system_mxcsr(void)
{
	unsigned int mask = 0;

	if (boot_cpu_has(X86_FEATURE_FXSR)) {
		/* Static because GCC does not get 16-byte stack alignment right: */
		static struct fxregs_state fxregs __initdata;

		asm volatile("fxsave %0" : "+m" (fxregs));

		mask = fxregs.mxcsr_mask;

		/*
		 * If zero then use the default features mask,
		 * which has all features set, except the
		 * denormals-are-zero feature bit:
		 */
		if (mask == 0)
			mask = 0x0000ffbf;
	}
	mxcsr_feature_mask &= mask;
}

/*
 * Once per bootup FPU initialization sequences that will run on most x86 CPUs:
 */
static void __init fpu__init_system_generic(void)
{
	/*
	 * Set up the legacy init FPU context. (xstate init might overwrite this
	 * with a more modern format, if the CPU supports it.)
	 */
	fpstate_init(&init_fpstate);

	fpu__init_system_mxcsr();
}

/*
 * Size of the FPU context state. All tasks in the system use the
 * same context size, regardless of what portion they use.
 * This is inherent to the XSAVE architecture which puts all state
 * components into a single, continuous memory block:
 */
unsigned int fpu_kernel_xstate_size;
EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);

/* Get alignment of the TYPE. */
#define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)

/*
 * Enforce that 'MEMBER' is the last field of 'TYPE'.
 *
 * Align the computed size with alignment of the TYPE,
 * because that's how C aligns structs.
 */
#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
	BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
					   TYPE_ALIGN(TYPE)))

/*
 * We append the 'struct fpu' to the task_struct:
 */
static void __init fpu__init_task_struct_size(void)
{
	int task_size = sizeof(struct task_struct);

	/*
	 * Subtract off the static size of the register state.
	 * It potentially has a bunch of padding.
	 */
	task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state);

	/*
	 * Add back the dynamically-calculated register state
	 * size.
	 */
	task_size += fpu_kernel_xstate_size;

	/*
	 * We dynamically size 'struct fpu', so we require that
	 * it be at the end of 'thread_struct' and that
	 * 'thread_struct' be at the end of 'task_struct'.  If
	 * you hit a compile error here, check the structure to
	 * see if something got added to the end.
	 */
	CHECK_MEMBER_AT_END_OF(struct fpu, state);
	CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
	CHECK_MEMBER_AT_END_OF(struct task_struct, thread);

	arch_task_struct_size = task_size;
}

/*
 * Set up the user and kernel xstate sizes based on the legacy FPU context size.
 *
 * We set this up first, and later it will be overwritten by
 * fpu__init_system_xstate() if the CPU knows about xstates.
 */
static void __init fpu__init_system_xstate_size_legacy(void)
{
	static int on_boot_cpu __initdata = 1;

	WARN_ON_FPU(!on_boot_cpu);
	on_boot_cpu = 0;

	/*
	 * Note that xstate sizes might be overwritten later during
	 * fpu__init_system_xstate().
	 */

	if (!boot_cpu_has(X86_FEATURE_FPU)) {
		/*
		 * Disable xsave as we do not support it if i387
		 * emulation is enabled.
		 */
		setup_clear_cpu_cap(X86_FEATURE_XSAVE);
		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
		fpu_kernel_xstate_size = sizeof(struct swregs_state);
	} else {
		if (boot_cpu_has(X86_FEATURE_FXSR))
			fpu_kernel_xstate_size =
				sizeof(struct fxregs_state);
		else
			fpu_kernel_xstate_size =
				sizeof(struct fregs_state);
	}

	fpu_user_xstate_size = fpu_kernel_xstate_size;
}

/*
 * Find supported xfeatures based on cpu features and command-line input.
 * This must be called after fpu__init_parse_early_param() is called and
 * xfeatures_mask is enumerated.
 */
u64 __init fpu__get_supported_xfeatures_mask(void)
{
	return XCNTXT_MASK;
}

/* Legacy code to initialize eager fpu mode. */
static void __init fpu__init_system_ctx_switch(void)
{
	static bool on_boot_cpu __initdata = 1;

	WARN_ON_FPU(!on_boot_cpu);
	on_boot_cpu = 0;
}

/*
 * We parse fpu parameters early because fpu__init_system() is executed
 * before parse_early_param().
 */
static void __init fpu__init_parse_early_param(void)
{
	char arg[32];
	char *argptr = arg;
	int bit;

	if (cmdline_find_option_bool(boot_command_line, "no387"))
		setup_clear_cpu_cap(X86_FEATURE_FPU);

	if (cmdline_find_option_bool(boot_command_line, "nofxsr")) {
		setup_clear_cpu_cap(X86_FEATURE_FXSR);
		setup_clear_cpu_cap(X86_FEATURE_FXSR_OPT);
		setup_clear_cpu_cap(X86_FEATURE_XMM);
	}

	if (cmdline_find_option_bool(boot_command_line, "noxsave"))
		fpu__xstate_clear_all_cpu_caps();

	if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);

	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
		setup_clear_cpu_cap(X86_FEATURE_XSAVES);

	if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
				sizeof(arg)) &&
	    get_option(&argptr, &bit) &&
	    bit >= 0 &&
	    bit < NCAPINTS * 32)
		setup_clear_cpu_cap(bit);
}

/*
 * Called on the boot CPU once per system bootup, to set up the initial
 * FPU state that is later cloned into all processes:
 */
void __init fpu__init_system(struct cpuinfo_x86 *c)
{
	fpu__init_parse_early_param();
	fpu__init_system_early_generic(c);

	/*
	 * The FPU has to be operational for some of the
	 * later FPU init activities:
	 */
	fpu__init_cpu();

	fpu__init_system_generic();
	fpu__init_system_xstate_size_legacy();
	fpu__init_system_xstate();
	fpu__init_task_struct_size();

	fpu__init_system_ctx_switch();
}