arch/x86/include/asm/system.h

#ifndef _ASM_X86_SYSTEM_H
#define _ASM_X86_SYSTEM_H

#include <asm/asm.h>
#include <asm/segment.h>
#include <asm/cpufeature.h>
#include <asm/cmpxchg.h>
#include <asm/nops.h>

#include <linux/kernel.h>
#include <linux/irqflags.h>

/* entries in ARCH_DLINFO: */
#ifdef CONFIG_IA32_EMULATION
# define AT_VECTOR_SIZE_ARCH 2
#else
# define AT_VECTOR_SIZE_ARCH 1
#endif

#ifdef CONFIG_X86_32

struct task_struct; /* one of the stranger aspects of C forward declarations */
struct task_struct *__switch_to(struct task_struct *prev,
				struct task_struct *next);

/*
 * Saving eflags is important. It switches not only IOPL between tasks,
 * it also protects other tasks from NT leaking through sysenter etc.
 */
#define switch_to(prev, next, last)					\
do {									\
	/*								\
	 * Context-switching clobbers all registers, so we clobber	\
	 * them explicitly, via unused output variables.		\
	 * (EAX and EBP is not listed because EBP is saved/restored	\
	 * explicitly for wchan access and EAX is the return value of	\
	 * __switch_to())						\
	 */								\
	unsigned long ebx, ecx, edx, esi, edi;				\
									\
	asm volatile("pushfl\n\t"		/* save    flags */	\
		     "pushl %%ebp\n\t"		/* save    EBP   */	\
		     "movl %%esp,%[prev_sp]\n\t"	/* save    ESP   */ \
		     "movl %[next_sp],%%esp\n\t"	/* restore ESP   */ \
		     "movl $1f,%[prev_ip]\n\t"	/* save    EIP   */	\
		     "pushl %[next_ip]\n\t"	/* restore EIP   */	\
		     "jmp __switch_to\n"	/* regparm call  */	\
		     "1:\t"						\
		     "popl %%ebp\n\t"		/* restore EBP   */	\
		     "popfl\n"			/* restore flags */	\
									\
		     /* output parameters */				\
		     : [prev_sp] "=m" (prev->thread.sp),		\
		       [prev_ip] "=m" (prev->thread.ip),		\
		       "=a" (last),					\
									\
		       /* clobbered output registers: */		\
		       "=b" (ebx), "=c" (ecx), "=d" (edx),		\
		       "=S" (esi), "=D" (edi)				\
		       							\
		       /* input parameters: */				\
		     : [next_sp]  "m" (next->thread.sp),		\
		       [next_ip]  "m" (next->thread.ip),		\
		       							\
		       /* regparm parameters for __switch_to(): */	\
		       [prev]     "a" (prev),				\
		       [next]     "d" (next)				\
									\
		     : /* reloaded segment registers */			\
			"memory");					\
} while (0)

/*
 * disable hlt during certain critical i/o operations
 */
#define HAVE_DISABLE_HLT
#else
#define __SAVE(reg, offset) "movq %%" #reg ",(14-" #offset ")*8(%%rsp)\n\t"
#define __RESTORE(reg, offset) "movq (14-" #offset ")*8(%%rsp),%%" #reg "\n\t"

/* frame pointer must be last for get_wchan */
#define SAVE_CONTEXT    "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t"
#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t"

#define __EXTRA_CLOBBER  \
	, "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \
	  "r12", "r13", "r14", "r15"

/* Save restore flags to clear handle leaking NT */
#define switch_to(prev, next, last) \
	asm volatile(SAVE_CONTEXT						    \
	     "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */	  \
	     "movq %P[threadrsp](%[next]),%%rsp\n\t" /* restore RSP */	  \
	     "call __switch_to\n\t"					  \
	     ".globl thread_return\n"					  \
	     "thread_return:\n\t"					  \
	     "movq %%gs:%P[pda_pcurrent],%%rsi\n\t"			  \
	     "movq %P[thread_info](%%rsi),%%r8\n\t"			  \
	     LOCK_PREFIX "btr  %[tif_fork],%P[ti_flags](%%r8)\n\t"	  \
	     "movq %%rax,%%rdi\n\t" 					  \
	     "jc   ret_from_fork\n\t"					  \
	     RESTORE_CONTEXT						  \
	     : "=a" (last)					  	  \
	     : [next] "S" (next), [prev] "D" (prev),			  \
	       [threadrsp] "i" (offsetof(struct task_struct, thread.sp)), \
	       [ti_flags] "i" (offsetof(struct thread_info, flags)),	  \
	       [tif_fork] "i" (TIF_FORK),			  	  \
	       [thread_info] "i" (offsetof(struct task_struct, stack)),   \
	       [pda_pcurrent] "i" (offsetof(struct x8664_pda, pcurrent))  \
	     : "memory", "cc" __EXTRA_CLOBBER)
#endif

#ifdef __KERNEL__
#define _set_base(addr, base) do { unsigned long __pr; \
__asm__ __volatile__ ("movw %%dx,%1\n\t" \
	"rorl $16,%%edx\n\t" \
	"movb %%dl,%2\n\t" \
	"movb %%dh,%3" \
	:"=&d" (__pr) \
	:"m" (*((addr)+2)), \
	 "m" (*((addr)+4)), \
	 "m" (*((addr)+7)), \
	 "0" (base) \
	); } while (0)

#define _set_limit(addr, limit) do { unsigned long __lr; \
__asm__ __volatile__ ("movw %%dx,%1\n\t" \
	"rorl $16,%%edx\n\t" \
	"movb %2,%%dh\n\t" \
	"andb $0xf0,%%dh\n\t" \
	"orb %%dh,%%dl\n\t" \
	"movb %%dl,%2" \
	:"=&d" (__lr) \
	:"m" (*(addr)), \
	 "m" (*((addr)+6)), \
	 "0" (limit) \
	); } while (0)

#define set_base(ldt, base) _set_base(((char *)&(ldt)) , (base))
#define set_limit(ldt, limit) _set_limit(((char *)&(ldt)) , ((limit)-1))

extern void native_load_gs_index(unsigned);

/*
 * Load a segment. Fall back on loading the zero
 * segment if something goes wrong..
 */
#define loadsegment(seg, value)			\
	asm volatile("\n"			\
		     "1:\t"			\
		     "movl %k0,%%" #seg "\n"	\
		     "2:\n"			\
		     ".section .fixup,\"ax\"\n"	\
		     "3:\t"			\
		     "movl %k1, %%" #seg "\n\t"	\
		     "jmp 2b\n"			\
		     ".previous\n"		\
		     _ASM_EXTABLE(1b,3b)	\
		     : :"r" (value), "r" (0) : "memory")


/*
 * Save a segment register away
 */
#define savesegment(seg, value)				\
	asm("mov %%" #seg ",%0":"=r" (value) : : "memory")

static inline unsigned long get_limit(unsigned long segment)
{
	unsigned long __limit;
	asm("lsll %1,%0" : "=r" (__limit) : "r" (segment));
	return __limit + 1;
}

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
 */
static 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");
}

#ifdef CONFIG_PARAVIRT
#include <asm/paravirt.h>
#else
#define read_cr0()	(native_read_cr0())
#define write_cr0(x)	(native_write_cr0(x))
#define read_cr2()	(native_read_cr2())
#define write_cr2(x)	(native_write_cr2(x))
#define read_cr3()	(native_read_cr3())
#define write_cr3(x)	(native_write_cr3(x))
#define read_cr4()	(native_read_cr4())
#define read_cr4_safe()	(native_read_cr4_safe())
#define write_cr4(x)	(native_write_cr4(x))
#define wbinvd()	(native_wbinvd())
#ifdef CONFIG_X86_64
#define read_cr8()	(native_read_cr8())
#define write_cr8(x)	(native_write_cr8(x))
#define load_gs_index   native_load_gs_index
#endif

/* Clear the 'TS' bit */
#define clts()		(native_clts())

#endif/* CONFIG_PARAVIRT */

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

#endif /* __KERNEL__ */

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

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

void disable_hlt(void);
void enable_hlt(void);

void cpu_idle_wait(void);

extern unsigned long arch_align_stack(unsigned long sp);
extern void free_init_pages(char *what, unsigned long begin, unsigned long end);

void default_idle(void);

/*
 * Force strict CPU ordering.
 * And yes, this is required on UP too when we're talking
 * to devices.
 */
#ifdef CONFIG_X86_32
/*
 * Some non-Intel clones support out of order store. wmb() ceases to be a
 * nop for these.
 */
#define mb() alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)
#define rmb() alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)
#define wmb() alternative("lock; addl $0,0(%%esp)", "sfence", X86_FEATURE_XMM)
#else
#define mb() 	asm volatile("mfence":::"memory")
#define rmb()	asm volatile("lfence":::"memory")
#define wmb()	asm volatile("sfence" ::: "memory")
#endif

/**
 * read_barrier_depends - Flush all pending reads that subsequents reads
 * depend on.
 *
 * No data-dependent reads from memory-like regions are ever reordered
 * over this barrier.  All reads preceding this primitive are guaranteed
 * to access memory (but not necessarily other CPUs' caches) before any
 * reads following this primitive that depend on the data return by
 * any of the preceding reads.  This primitive is much lighter weight than
 * rmb() on most CPUs, and is never heavier weight than is
 * rmb().
 *
 * These ordering constraints are respected by both the local CPU
 * and the compiler.
 *
 * Ordering is not guaranteed by anything other than these primitives,
 * not even by data dependencies.  See the documentation for
 * memory_barrier() for examples and URLs to more information.
 *
 * For example, the following code would force ordering (the initial
 * value of "a" is zero, "b" is one, and "p" is "&a"):
 *
 * <programlisting>
 *	CPU 0				CPU 1
 *
 *	b = 2;
 *	memory_barrier();
 *	p = &b;				q = p;
 *					read_barrier_depends();
 *					d = *q;
 * </programlisting>
 *
 * because the read of "*q" depends on the read of "p" and these
 * two reads are separated by a read_barrier_depends().  However,
 * the following code, with the same initial values for "a" and "b":
 *
 * <programlisting>
 *	CPU 0				CPU 1
 *
 *	a = 2;
 *	memory_barrier();
 *	b = 3;				y = b;
 *					read_barrier_depends();
 *					x = a;
 * </programlisting>
 *
 * does not enforce ordering, since there is no data dependency between
 * the read of "a" and the read of "b".  Therefore, on some CPUs, such
 * as Alpha, "y" could be set to 3 and "x" to 0.  Use rmb()
 * in cases like this where there are no data dependencies.
 **/

#define read_barrier_depends()	do { } while (0)

#ifdef CONFIG_SMP
#define smp_mb()	mb()
#ifdef CONFIG_X86_PPRO_FENCE
# define smp_rmb()	rmb()
#else
# define smp_rmb()	barrier()
#endif
#ifdef CONFIG_X86_OOSTORE
# define smp_wmb() 	wmb()
#else
# define smp_wmb()	barrier()
#endif
#define smp_read_barrier_depends()	read_barrier_depends()
#define set_mb(var, value) do { (void)xchg(&var, value); } while (0)
#else
#define smp_mb()	barrier()
#define smp_rmb()	barrier()
#define smp_wmb()	barrier()
#define smp_read_barrier_depends()	do { } while (0)
#define set_mb(var, value) do { var = value; barrier(); } while (0)
#endif

/*
 * Stop RDTSC speculation. This is needed when you need to use RDTSC
 * (or get_cycles or vread that possibly accesses the TSC) in a defined
 * code region.
 *
 * (Could use an alternative three way for this if there was one.)
 */
static inline void rdtsc_barrier(void)
{
	alternative(ASM_NOP3, "mfence", X86_FEATURE_MFENCE_RDTSC);
	alternative(ASM_NOP3, "lfence", X86_FEATURE_LFENCE_RDTSC);
}

#endif /* _ASM_X86_SYSTEM_H */