linux/arch/x86/include/asm/special_insns.h

#ifndef _ASM_X86_SPECIAL_INSNS_H
#define _ASM_X86_SPECIAL_INSNS_H


#ifdef __KERNEL__

static inline void native_clts(void)
{
	asm volatile("clts");
}

/*
 * Volatile isn't enough to prevent the compiler from reordering the
 * read/write functions for the control registers and messing everything up.
 * A memory clobber would solve the problem, but would prevent reordering of
 * all loads stores around it, which can hurt performance. Solution is to
 * use a variable and mimic reads and writes to it to enforce serialization
 */
extern unsigned long __force_order;

static inline unsigned long native_read_cr0(void)
{
	unsigned long val;
	asm volatile("mov %%cr0,%0\n\t" : "=r" (val), "=m" (__force_order));
	return val;
}

static inline void native_write_cr0(unsigned long val)
{
	asm volatile("mov %0,%%cr0": : "r" (val), "m" (__force_order));
}

static inline unsigned long native_read_cr2(void)
{
	unsigned long val;
	asm volatile("mov %%cr2,%0\n\t" : "=r" (val), "=m" (__force_order));
	return val;
}

static inline void native_write_cr2(unsigned long val)
{
	asm volatile("mov %0,%%cr2": : "r" (val), "m" (__force_order));
}

static inline unsigned long native_read_cr3(void)
{
	unsigned long val;
	asm volatile("mov %%cr3,%0\n\t" : "=r" (val), "=m" (__force_order));
	return val;
}

static inline void native_write_cr3(unsigned long val)
{
	asm volatile("mov %0,%%cr3": : "r" (val), "m" (__force_order));
}

static inline unsigned long native_read_cr4(void)
{
	unsigned long val;
	asm volatile("mov %%cr4,%0\n\t" : "=r" (val), "=m" (__force_order));
	return val;
}

static inline unsigned long native_read_cr4_safe(void)
{
	unsigned long val;
	/* This could fault if %cr4 does not exist. In x86_64, a cr4 always
	 * exists, so it will never fail. */
#ifdef CONFIG_X86_32
	asm volatile("1: mov %%cr4, %0\n"
		     "2:\n"
		     _ASM_EXTABLE(1b, 2b)
		     : "=r" (val), "=m" (__force_order) : "0" (0));
#else
	val = native_read_cr4();
#endif
	return val;
}

static inline void native_write_cr4(unsigned long val)
{
	asm volatile("mov %0,%%cr4": : "r" (val), "m" (__force_order));
}

#ifdef CONFIG_X86_64
static inline unsigned long native_read_cr8(void)
{
	unsigned long cr8;
	asm volatile("movq %%cr8,%0" : "=r" (cr8));
	return cr8;
}

static inline void native_write_cr8(unsigned long val)
{
	asm volatile("movq %0,%%cr8" :: "r" (val) : "memory");
}
#endif

static inline void native_wbinvd(void)
{
	asm volatile("wbinvd": : :"memory");
}

extern asmlinkage void native_load_gs_index(unsigned);

#ifdef CONFIG_PARAVIRT
#include <asm/paravirt.h>
#else

static inline unsigned long read_cr0(void)
{
	return native_read_cr0();
}

static inline void write_cr0(unsigned long x)
{
	native_write_cr0(x);
}

static inline unsigned long read_cr2(void)
{
	return native_read_cr2();
}

static inline void write_cr2(unsigned long x)
{
	native_write_cr2(x);
}

static inline unsigned long read_cr3(void)
{
	return native_read_cr3();
}

static inline void write_cr3(unsigned long x)
{
	native_write_cr3(x);
}

static inline unsigned long read_cr4(void)
{
	return native_read_cr4();
}

static inline unsigned long read_cr4_safe(void)
{
	return native_read_cr4_safe();
}

static inline void write_cr4(unsigned long x)
{
	native_write_cr4(x);
}

static inline void wbinvd(void)
{
	native_wbinvd();
}

#ifdef CONFIG_X86_64

static inline unsigned long read_cr8(void)
{
	return native_read_cr8();
}

static inline void write_cr8(unsigned long x)
{
	native_write_cr8(x);
}

static inline void load_gs_index(unsigned selector)
{
	native_load_gs_index(selector);
}

#endif

/* Clear the 'TS' bit */
static inline void clts(void)
{
	native_clts();
}

#endif/* CONFIG_PARAVIRT */

#define stts() write_cr0(read_cr0() | X86_CR0_TS)

static inline void clflush(volatile void *__p)
{
	asm volatile("clflush %0" : "+m" (*(volatile char __force *)__p));
}

static inline void clflushopt(volatile void *__p)
{
	alternative_io(".byte " __stringify(NOP_DS_PREFIX) "; clflush %P0",
		       ".byte 0x66; clflush %P0",
		       X86_FEATURE_CLFLUSHOPT,
		       "+m" (*(volatile char __force *)__p));
}

#define nop() asm volatile ("nop")


#endif /* __KERNEL__ */

#endif /* _ASM_X86_SPECIAL_INSNS_H */