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 struct alt_instr {
  43         u8 *instr;              /* original instruction */
  44         u8 *replacement;
  45         u8  cpuid;              /* cpuid bit set for replacement */
  46         u8  instrlen;           /* length of original instruction */
  47         u8  replacementlen;     /* length of new instruction, <= instrlen */
  48         u8  pad1;
  49 #ifdef CONFIG_X86_64
  50         u32 pad2;
  51 #endif
  52 };
  53
  54 extern void alternative_instructions(void);
  55 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  56
  57 struct module;
  58
  59 #ifdef CONFIG_SMP
  60 extern void alternatives_smp_module_add(struct module *mod, char *name,
  61                                         void *locks, void *locks_end,
  62                                         void *text, void *text_end);
  63 extern void alternatives_smp_module_del(struct module *mod);
  64 extern void alternatives_smp_switch(int smp);
  65 extern int alternatives_text_reserved(void *start, void *end);
  66 #else
  67 static inline void alternatives_smp_module_add(struct module *mod, char *name,
  68                                                void *locks, void *locks_end,
  69                                                void *text, void *text_end) {}
  70 static inline void alternatives_smp_module_del(struct module *mod) {}
  71 static inline void alternatives_smp_switch(int smp) {}
  72 static inline int alternatives_text_reserved(void *start, void *end)
  73 {
  74         return 0;
  75 }
  76 #endif  /* CONFIG_SMP */
  77
  78 /* alternative assembly primitive: */
  79 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
  80                                                                         \
  81       "661:\n\t" oldinstr "\n662:\n"                                    \
  82       ".section .altinstructions,\"a\"\n"                               \
  83       _ASM_ALIGN "\n"                                                   \
  84       _ASM_PTR "661b\n"                         /* label           */   \
  85       _ASM_PTR "663f\n"                         /* new instruction */   \
  86       "  .byte " __stringify(feature) "\n"      /* feature bit     */   \
  87       "  .byte 662b-661b\n"                     /* sourcelen       */   \
  88       "  .byte 664f-663f\n"                     /* replacementlen  */   \
  89       "  .byte 0xff + (664f-663f) - (662b-661b)\n" /* rlen <= slen */   \
  90       ".previous\n"                                                     \
  91       ".section .altinstr_replacement, \"ax\"\n"                        \
  92       "663:\n\t" newinstr "\n664:\n"            /* replacement     */   \
  93       ".previous"
  94
  95 /*
  96  * This must be included *after* the definition of ALTERNATIVE due to
  97  * <asm/arch_hweight.h>
  98  */
  99 #include <asm/cpufeature.h>
 100
 101 /*
 102  * Alternative instructions for different CPU types or capabilities.
 103  *
 104  * This allows to use optimized instructions even on generic binary
 105  * kernels.
 106  *
 107  * length of oldinstr must be longer or equal the length of newinstr
 108  * It can be padded with nops as needed.
 109  *
 110  * For non barrier like inlines please define new variants
 111  * without volatile and memory clobber.
 112  */
 113 #define alternative(oldinstr, newinstr, feature)                        \
 114         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 115
 116 /*
 117  * Alternative inline assembly with input.
 118  *
 119  * Pecularities:
 120  * No memory clobber here.
 121  * Argument numbers start with 1.
 122  * Best is to use constraints that are fixed size (like (%1) ... "r")
 123  * If you use variable sized constraints like "m" or "g" in the
 124  * replacement make sure to pad to the worst case length.
 125  * Leaving an unused argument 0 to keep API compatibility.
 126  */
 127 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 128         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 129                 : : "i" (0), ## input)
 130
 131 /* Like alternative_input, but with a single output argument */
 132 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 133         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 134                 : output : "i" (0), ## input)
 135
 136 /* Like alternative_io, but for replacing a direct call with another one. */
 137 #define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 138         asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 139                 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 140
 141 /*
 142  * use this macro(s) if you need more than one output parameter
 143  * in alternative_io
 144  */
 145 #define ASM_OUTPUT2(a...) a
 146
 147 struct paravirt_patch_site;
 148 #ifdef CONFIG_PARAVIRT
 149 void apply_paravirt(struct paravirt_patch_site *start,
 150                     struct paravirt_patch_site *end);
 151 #else
 152 static inline void apply_paravirt(struct paravirt_patch_site *start,
 153                                   struct paravirt_patch_site *end)
 154 {}
 155 #define __parainstructions      NULL
 156 #define __parainstructions_end  NULL
 157 #endif
 158
 159 /*
 160  * Clear and restore the kernel write-protection flag on the local CPU.
 161  * Allows the kernel to edit read-only pages.
 162  * Side-effect: any interrupt handler running between save and restore will have
 163  * the ability to write to read-only pages.
 164  *
 165  * Warning:
 166  * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
 167  * no thread can be preempted in the instructions being modified (no iret to an
 168  * invalid instruction possible) or if the instructions are changed from a
 169  * consistent state to another consistent state atomically.
 170  * More care must be taken when modifying code in the SMP case because of
 171  * Intel's errata. text_poke_smp() takes care that errata, but still
 172  * doesn't support NMI/MCE handler code modifying.
 173  * On the local CPU you need to be protected again NMI or MCE handlers seeing an
 174  * inconsistent instruction while you patch.
 175  */
 176 extern void *text_poke(void *addr, const void *opcode, size_t len);
 177 extern void *text_poke_smp(void *addr, const void *opcode, size_t len);
 178
 179 #endif /* _ASM_X86_ALTERNATIVE_H */