init.c 7.46 KB
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// SPDX-License-Identifier: GPL-2.0-only
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/*
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 * x86 FPU boot time init code:
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 */
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#include <asm/fpu/internal.h>
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#include <asm/tlbflush.h>
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#include <asm/setup.h>
#include <asm/cmdline.h>
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#include <linux/sched.h>
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#include <linux/sched/task.h>
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#include <linux/init.h>
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/*
 * 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;

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	if (boot_cpu_has(X86_FEATURE_FXSR))
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		cr4_mask |= X86_CR4_OSFXSR;
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	if (boot_cpu_has(X86_FEATURE_XMM))
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		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 */
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	if (!boot_cpu_has(X86_FEATURE_FPU))
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		cr0 |= X86_CR0_EM;
	write_cr0(cr0);
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	/* Flush out any pending x87 state: */
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#ifdef CONFIG_MATH_EMULATION
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	if (!boot_cpu_has(X86_FEATURE_FPU))
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		fpstate_init_soft(&current->thread.fpu.state.soft);
	else
#endif
		asm volatile ("fninit");
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}

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

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

	fsw = fcw = 0xffff;

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

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

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/*
 * Boot time FPU feature detection code:
 */
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unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
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EXPORT_SYMBOL_GPL(mxcsr_feature_mask);
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static void __init fpu__init_system_mxcsr(void)
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{
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	unsigned int mask = 0;
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	if (boot_cpu_has(X86_FEATURE_FXSR)) {
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		/* Static because GCC does not get 16-byte stack alignment right: */
		static struct fxregs_state fxregs __initdata;
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		asm volatile("fxsave %0" : "+m" (fxregs));
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		mask = fxregs.mxcsr_mask;
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		/*
		 * If zero then use the default features mask,
		 * which has all features set, except the
		 * denormals-are-zero feature bit:
		 */
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		if (mask == 0)
			mask = 0x0000ffbf;
	}
	mxcsr_feature_mask &= mask;
}

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

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/*
 * 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:
 */
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unsigned int fpu_kernel_xstate_size;
EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);
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/* 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.
 */
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#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
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	BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
					   TYPE_ALIGN(TYPE)))
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/*
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 * We append the 'struct fpu' to the task_struct:
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 */
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static void __init fpu__init_task_struct_size(void)
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{
	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.
	 */
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	task_size += fpu_kernel_xstate_size;
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	/*
	 * 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);

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	arch_task_struct_size = task_size;
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}

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/*
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 * Set up the user and kernel xstate sizes based on the legacy FPU context size.
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 *
 * We set this up first, and later it will be overwritten by
 * fpu__init_system_xstate() if the CPU knows about xstates.
 */
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static void __init fpu__init_system_xstate_size_legacy(void)
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{
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	static int on_boot_cpu __initdata = 1;
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	WARN_ON_FPU(!on_boot_cpu);
	on_boot_cpu = 0;

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

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	if (!boot_cpu_has(X86_FEATURE_FPU)) {
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		/*
		 * 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);
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		fpu_kernel_xstate_size = sizeof(struct swregs_state);
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	} else {
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		if (boot_cpu_has(X86_FEATURE_FXSR))
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			fpu_kernel_xstate_size =
				sizeof(struct fxregs_state);
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		else
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			fpu_kernel_xstate_size =
				sizeof(struct fregs_state);
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	}
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	fpu_user_xstate_size = fpu_kernel_xstate_size;
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}

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/*
 * 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)
{
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	return XCNTXT_MASK;
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}

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/* Legacy code to initialize eager fpu mode. */
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static void __init fpu__init_system_ctx_switch(void)
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{
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	static bool on_boot_cpu __initdata = 1;
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	WARN_ON_FPU(!on_boot_cpu);
	on_boot_cpu = 0;
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}

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

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	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);
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	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);
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}

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

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	/*
	 * The FPU has to be operational for some of the
	 * later FPU init activities:
	 */
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	fpu__init_cpu();
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	fpu__init_system_generic();
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	fpu__init_system_xstate_size_legacy();
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	fpu__init_system_xstate();
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	fpu__init_task_struct_size();
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	fpu__init_system_ctx_switch();
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}