arch/x86/include/asm/alternative.h

   1 #ifndef _ASM_X86_ALTERNATIVE_H
   2 #define _ASM_X86_ALTERNATIVE_H
   3
   4 #include <linux/types.h>
   5 #include <linux/stddef.h>
   6 #include <linux/stringify.h>
   7 #include <asm/asm.h>
   8
   9 /*
  10  * Alternative inline assembly for SMP.
  11  *
  12  * The LOCK_PREFIX macro defined here replaces the LOCK and
  13  * LOCK_PREFIX macros used everywhere in the source tree.
  14  *
  15  * SMP alternatives use the same data structures as the other
  16  * alternatives and the X86_FEATURE_UP flag to indicate the case of a
  17  * UP system running a SMP kernel.  The existing apply_alternatives()
  18  * works fine for patching a SMP kernel for UP.
  19  *
  20  * The SMP alternative tables can be kept after boot and contain both
  21  * UP and SMP versions of the instructions to allow switching back to
  22  * SMP at runtime, when hotplugging in a new CPU, which is especially
  23  * useful in virtualized environments.
  24  *
  25  * The very common lock prefix is handled as special case in a
  26  * separate table which is a pure address list without replacement ptr
  27  * and size information.  That keeps the table sizes small.
  28  */
  29
  30 #ifdef CONFIG_SMP
  31 #define LOCK_PREFIX \
  32                 ".section .smp_locks,\"a\"\n"   \
  33                 _ASM_ALIGN "\n"                 \
  34                 _ASM_PTR "661f\n" /* address */ \
  35                 ".previous\n"                   \
  36                 "661:\n\tlock; "
  37
  38 #else /* ! CONFIG_SMP */
  39 #define LOCK_PREFIX ""
  40 #endif
  41
  42 /* This must be included *after* the definition of LOCK_PREFIX */
  43 #include <asm/cpufeature.h>
  44
  45 struct alt_instr {
  46         u8 *instr;              /* original instruction */
  47         u8 *replacement;
  48         u8  cpuid;              /* cpuid bit set for replacement */
  49         u8  instrlen;           /* length of original instruction */
  50         u8  replacementlen;     /* length of new instruction, <= instrlen */
  51         u8  pad1;
  52 #ifdef CONFIG_X86_64
  53         u32 pad2;
  54 #endif
  55 };
  56
  57 extern void alternative_instructions(void);
  58 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  59
  60 struct module;
  61
  62 #ifdef CONFIG_SMP
  63 extern void alternatives_smp_module_add(struct module *mod, char *name,
  64                                         void *locks, void *locks_end,
  65                                         void *text, void *text_end);
  66 extern void alternatives_smp_module_del(struct module *mod);
  67 extern void alternatives_smp_switch(int smp);
  68 #else
  69 static inline void alternatives_smp_module_add(struct module *mod, char *name,
  70                                                void *locks, void *locks_end,
  71                                                void *text, void *text_end) {}
  72 static inline void alternatives_smp_module_del(struct module *mod) {}
  73 static inline void alternatives_smp_switch(int smp) {}
  74 #endif  /* CONFIG_SMP */
  75
  76 /* alternative assembly primitive: */
  77 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
  78                                                                         \
  79       "661:\n\t" oldinstr "\n662:\n"                                    \
  80       ".section .altinstructions,\"a\"\n"                               \
  81       _ASM_ALIGN "\n"                                                   \
  82       _ASM_PTR "661b\n"                         /* label           */   \
  83       _ASM_PTR "663f\n"                         /* new instruction */   \
  84       "  .byte " __stringify(feature) "\n"      /* feature bit     */   \
  85       "  .byte 662b-661b\n"                     /* sourcelen       */   \
  86       "  .byte 664f-663f\n"                     /* replacementlen  */   \
  87       ".previous\n"                                                     \
  88       ".section .altinstr_replacement, \"ax\"\n"                        \
  89       "663:\n\t" newinstr "\n664:\n"            /* replacement     */   \
  90       ".previous"
  91
  92 /*
  93  * Alternative instructions for different CPU types or capabilities.
  94  *
  95  * This allows to use optimized instructions even on generic binary
  96  * kernels.
  97  *
  98  * length of oldinstr must be longer or equal the length of newinstr
  99  * It can be padded with nops as needed.
 100  *
 101  * For non barrier like inlines please define new variants
 102  * without volatile and memory clobber.
 103  */
 104 #define alternative(oldinstr, newinstr, feature)                        \
 105         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 106
 107 /*
 108  * Alternative inline assembly with input.
 109  *
 110  * Pecularities:
 111  * No memory clobber here.
 112  * Argument numbers start with 1.
 113  * Best is to use constraints that are fixed size (like (%1) ... "r")
 114  * If you use variable sized constraints like "m" or "g" in the
 115  * replacement make sure to pad to the worst case length.
 116  * Leaving an unused argument 0 to keep API compatibility.
 117  */
 118 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 119         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 120                 : : "i" (0), ## input)
 121
 122 /* Like alternative_input, but with a single output argument */
 123 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 124         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 125                 : output : "i" (0), ## input)
 126
 127 /*
 128  * use this macro(s) if you need more than one output parameter
 129  * in alternative_io
 130  */
 131 #define ASM_OUTPUT2(a, b) a, b
 132
 133 struct paravirt_patch_site;
 134 #ifdef CONFIG_PARAVIRT
 135 void apply_paravirt(struct paravirt_patch_site *start,
 136                     struct paravirt_patch_site *end);
 137 #else
 138 static inline void apply_paravirt(struct paravirt_patch_site *start,
 139                                   struct paravirt_patch_site *end)
 140 {}
 141 #define __parainstructions      NULL
 142 #define __parainstructions_end  NULL
 143 #endif
 144
 145 /*
 146  * Clear and restore the kernel write-protection flag on the local CPU.
 147  * Allows the kernel to edit read-only pages.
 148  * Side-effect: any interrupt handler running between save and restore will have
 149  * the ability to write to read-only pages.
 150  *
 151  * Warning:
 152  * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
 153  * no thread can be preempted in the instructions being modified (no iret to an
 154  * invalid instruction possible) or if the instructions are changed from a
 155  * consistent state to another consistent state atomically.
 156  * More care must be taken when modifying code in the SMP case because of
 157  * Intel's errata.
 158  * On the local CPU you need to be protected again NMI or MCE handlers seeing an
 159  * inconsistent instruction while you patch.
 160  */
 161 extern void *text_poke(void *addr, const void *opcode, size_t len);
 162
 163 #endif /* _ASM_X86_ALTERNATIVE_H */