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_HERE \
  32                 ".section .smp_locks,\"a\"\n"   \
  33                 ".balign 4\n"                   \
  34                 ".long 671f - .\n" /* offset */ \
  35                 ".previous\n"                   \
  36                 "671:"
  37
  38 #define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
  39
  40 #else /* ! CONFIG_SMP */
  41 #define LOCK_PREFIX_HERE ""
  42 #define LOCK_PREFIX ""
  43 #endif
  44
  45 struct alt_instr {
  46         s32 instr_offset;       /* original instruction */
  47         s32 repl_offset;        /* offset to replacement instruction */
  48         u16 cpuid;              /* cpuid bit set for replacement */
  49         u8  instrlen;           /* length of original instruction */
  50         u8  replacementlen;     /* length of new instruction, <= instrlen */
  51 #ifdef CONFIG_X86_64
  52         u32 pad2;
  53 #endif
  54 };
  55
  56 extern void alternative_instructions(void);
  57 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  58
  59 struct module;
  60
  61 #ifdef CONFIG_SMP
  62 extern void alternatives_smp_module_add(struct module *mod, char *name,
  63                                         void *locks, void *locks_end,
  64                                         void *text, void *text_end);
  65 extern void alternatives_smp_module_del(struct module *mod);
  66 extern void alternatives_smp_switch(int smp);
  67 extern int alternatives_text_reserved(void *start, void *end);
  68 extern bool skip_smp_alternatives;
  69 #else
  70 static inline void alternatives_smp_module_add(struct module *mod, char *name,
  71                                                void *locks, void *locks_end,
  72                                                void *text, void *text_end) {}
  73 static inline void alternatives_smp_module_del(struct module *mod) {}
  74 static inline void alternatives_smp_switch(int smp) {}
  75 static inline int alternatives_text_reserved(void *start, void *end)
  76 {
  77         return 0;
  78 }
  79 #endif  /* CONFIG_SMP */
  80
  81 /* alternative assembly primitive: */
  82 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
  83                                                                         \
  84       "661:\n\t" oldinstr "\n662:\n"                                    \
  85       ".section .altinstructions,\"a\"\n"                               \
  86       _ASM_ALIGN "\n"                                                   \
  87       "  .long 661b - .\n"                      /* label           */   \
  88       "  .long 663f - .\n"                      /* new instruction */   \
  89       "  .word " __stringify(feature) "\n"      /* feature bit     */   \
  90       "  .byte 662b-661b\n"                     /* sourcelen       */   \
  91       "  .byte 664f-663f\n"                     /* replacementlen  */   \
  92       ".previous\n"                                                     \
  93       ".section .discard,\"aw\",@progbits\n"                            \
  94       "  .byte 0xff + (664f-663f) - (662b-661b)\n" /* rlen <= slen */   \
  95       ".previous\n"                                                     \
  96       ".section .altinstr_replacement, \"ax\"\n"                        \
  97       "663:\n\t" newinstr "\n664:\n"            /* replacement     */   \
  98       ".previous"
  99
 100 /*
 101  * This must be included *after* the definition of ALTERNATIVE due to
 102  * <asm/arch_hweight.h>
 103  */
 104 #include <asm/cpufeature.h>
 105
 106 /*
 107  * Alternative instructions for different CPU types or capabilities.
 108  *
 109  * This allows to use optimized instructions even on generic binary
 110  * kernels.
 111  *
 112  * length of oldinstr must be longer or equal the length of newinstr
 113  * It can be padded with nops as needed.
 114  *
 115  * For non barrier like inlines please define new variants
 116  * without volatile and memory clobber.
 117  */
 118 #define alternative(oldinstr, newinstr, feature)                        \
 119         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 120
 121 /*
 122  * Alternative inline assembly with input.
 123  *
 124  * Pecularities:
 125  * No memory clobber here.
 126  * Argument numbers start with 1.
 127  * Best is to use constraints that are fixed size (like (%1) ... "r")
 128  * If you use variable sized constraints like "m" or "g" in the
 129  * replacement make sure to pad to the worst case length.
 130  * Leaving an unused argument 0 to keep API compatibility.
 131  */
 132 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 133         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 134                 : : "i" (0), ## input)
 135
 136 /* Like alternative_input, but with a single output argument */
 137 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 138         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 139                 : output : "i" (0), ## input)
 140
 141 /* Like alternative_io, but for replacing a direct call with another one. */
 142 #define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 143         asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 144                 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 145
 146 /*
 147  * use this macro(s) if you need more than one output parameter
 148  * in alternative_io
 149  */
 150 #define ASM_OUTPUT2(a...) a
 151
 152 struct paravirt_patch_site;
 153 #ifdef CONFIG_PARAVIRT
 154 void apply_paravirt(struct paravirt_patch_site *start,
 155                     struct paravirt_patch_site *end);
 156 #else
 157 static inline void apply_paravirt(struct paravirt_patch_site *start,
 158                                   struct paravirt_patch_site *end)
 159 {}
 160 #define __parainstructions      NULL
 161 #define __parainstructions_end  NULL
 162 #endif
 163
 164 extern void *text_poke_early(void *addr, const void *opcode, size_t len);
 165
 166 /*
 167  * Clear and restore the kernel write-protection flag on the local CPU.
 168  * Allows the kernel to edit read-only pages.
 169  * Side-effect: any interrupt handler running between save and restore will have
 170  * the ability to write to read-only pages.
 171  *
 172  * Warning:
 173  * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
 174  * no thread can be preempted in the instructions being modified (no iret to an
 175  * invalid instruction possible) or if the instructions are changed from a
 176  * consistent state to another consistent state atomically.
 177  * More care must be taken when modifying code in the SMP case because of
 178  * Intel's errata. text_poke_smp() takes care that errata, but still
 179  * doesn't support NMI/MCE handler code modifying.
 180  * On the local CPU you need to be protected again NMI or MCE handlers seeing an
 181  * inconsistent instruction while you patch.
 182  */
 183 struct text_poke_param {
 184         void *addr;
 185         const void *opcode;
 186         size_t len;
 187 };
 188
 189 extern void *text_poke(void *addr, const void *opcode, size_t len);
 190 extern void *text_poke_smp(void *addr, const void *opcode, size_t len);
 191 extern void text_poke_smp_batch(struct text_poke_param *params, int n);
 192
 193 #endif /* _ASM_X86_ALTERNATIVE_H */