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                 ".pushsection .smp_locks,\"a\"\n"       \
  33                 ".balign 4\n"                           \
  34                 ".long 671f - .\n" /* offset */         \
  35                 ".popsection\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 };
  52
  53 extern void alternative_instructions(void);
  54 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  55
  56 struct module;
  57
  58 #ifdef CONFIG_SMP
  59 extern void alternatives_smp_module_add(struct module *mod, char *name,
  60                                         void *locks, void *locks_end,
  61                                         void *text, void *text_end);
  62 extern void alternatives_smp_module_del(struct module *mod);
  63 extern void alternatives_enable_smp(void);
  64 extern int alternatives_text_reserved(void *start, void *end);
  65 extern bool skip_smp_alternatives;
  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_enable_smp(void) {}
  72 static inline int alternatives_text_reserved(void *start, void *end)
  73 {
  74         return 0;
  75 }
  76 #endif  /* CONFIG_SMP */
  77
  78 #define OLDINSTR(oldinstr)      "661:\n\t" oldinstr "\n662:\n"
  79
  80 #define b_replacement(number)   "663"#number
  81 #define e_replacement(number)   "664"#number
  82
  83 #define alt_slen "662b-661b"
  84 #define alt_rlen(number) e_replacement(number)"f-"b_replacement(number)"f"
  85
  86 #define ALTINSTR_ENTRY(feature, number)                                       \
  87         " .long 661b - .\n"                             /* label           */ \
  88         " .long " b_replacement(number)"f - .\n"        /* new instruction */ \
  89         " .word " __stringify(feature) "\n"             /* feature bit     */ \
  90         " .byte " alt_slen "\n"                         /* source len      */ \
  91         " .byte " alt_rlen(number) "\n"                 /* replacement len */
  92
  93 #define DISCARD_ENTRY(number)                           /* rlen <= slen */    \
  94         " .byte 0xff + (" alt_rlen(number) ") - (" alt_slen ")\n"
  95
  96 #define ALTINSTR_REPLACEMENT(newinstr, feature, number) /* replacement */     \
  97         b_replacement(number)":\n\t" newinstr "\n" e_replacement(number) ":\n\t"
  98
  99 /* alternative assembly primitive: */
 100 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
 101         OLDINSTR(oldinstr)                                              \
 102         ".pushsection .altinstructions,\"a\"\n"                         \
 103         ALTINSTR_ENTRY(feature, 1)                                      \
 104         ".popsection\n"                                                 \
 105         ".pushsection .discard,\"aw\",@progbits\n"                      \
 106         DISCARD_ENTRY(1)                                                \
 107         ".popsection\n"                                                 \
 108         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 109         ALTINSTR_REPLACEMENT(newinstr, feature, 1)                      \
 110         ".popsection"
 111
 112 #define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
 113         OLDINSTR(oldinstr)                                              \
 114         ".pushsection .altinstructions,\"a\"\n"                         \
 115         ALTINSTR_ENTRY(feature1, 1)                                     \
 116         ALTINSTR_ENTRY(feature2, 2)                                     \
 117         ".popsection\n"                                                 \
 118         ".pushsection .discard,\"aw\",@progbits\n"                      \
 119         DISCARD_ENTRY(1)                                                \
 120         DISCARD_ENTRY(2)                                                \
 121         ".popsection\n"                                                 \
 122         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 123         ALTINSTR_REPLACEMENT(newinstr1, feature1, 1)                    \
 124         ALTINSTR_REPLACEMENT(newinstr2, feature2, 2)                    \
 125         ".popsection"
 126
 127 /*
 128  * This must be included *after* the definition of ALTERNATIVE due to
 129  * <asm/arch_hweight.h>
 130  */
 131 #include <asm/cpufeature.h>
 132
 133 /*
 134  * Alternative instructions for different CPU types or capabilities.
 135  *
 136  * This allows to use optimized instructions even on generic binary
 137  * kernels.
 138  *
 139  * length of oldinstr must be longer or equal the length of newinstr
 140  * It can be padded with nops as needed.
 141  *
 142  * For non barrier like inlines please define new variants
 143  * without volatile and memory clobber.
 144  */
 145 #define alternative(oldinstr, newinstr, feature)                        \
 146         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 147
 148 /*
 149  * Alternative inline assembly with input.
 150  *
 151  * Pecularities:
 152  * No memory clobber here.
 153  * Argument numbers start with 1.
 154  * Best is to use constraints that are fixed size (like (%1) ... "r")
 155  * If you use variable sized constraints like "m" or "g" in the
 156  * replacement make sure to pad to the worst case length.
 157  * Leaving an unused argument 0 to keep API compatibility.
 158  */
 159 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 160         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 161                 : : "i" (0), ## input)
 162
 163 /* Like alternative_input, but with a single output argument */
 164 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 165         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 166                 : output : "i" (0), ## input)
 167
 168 /* Like alternative_io, but for replacing a direct call with another one. */
 169 #define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 170         asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 171                 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 172
 173 /*
 174  * Like alternative_call, but there are two features and respective functions.
 175  * If CPU has feature2, function2 is used.
 176  * Otherwise, if CPU has feature1, function1 is used.
 177  * Otherwise, old function is used.
 178  */
 179 #define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
 180                            output, input...)                                  \
 181         asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
 182                 "call %P[new2]", feature2)                                    \
 183                 : output : [old] "i" (oldfunc), [new1] "i" (newfunc1),        \
 184                 [new2] "i" (newfunc2), ## input)
 185
 186 /*
 187  * use this macro(s) if you need more than one output parameter
 188  * in alternative_io
 189  */
 190 #define ASM_OUTPUT2(a...) a
 191
 192 /*
 193  * use this macro if you need clobbers but no inputs in
 194  * alternative_{input,io,call}()
 195  */
 196 #define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
 197
 198 struct paravirt_patch_site;
 199 #ifdef CONFIG_PARAVIRT
 200 void apply_paravirt(struct paravirt_patch_site *start,
 201                     struct paravirt_patch_site *end);
 202 #else
 203 static inline void apply_paravirt(struct paravirt_patch_site *start,
 204                                   struct paravirt_patch_site *end)
 205 {}
 206 #define __parainstructions      NULL
 207 #define __parainstructions_end  NULL
 208 #endif
 209
 210 extern void *text_poke_early(void *addr, const void *opcode, size_t len);
 211
 212 /*
 213  * Clear and restore the kernel write-protection flag on the local CPU.
 214  * Allows the kernel to edit read-only pages.
 215  * Side-effect: any interrupt handler running between save and restore will have
 216  * the ability to write to read-only pages.
 217  *
 218  * Warning:
 219  * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
 220  * no thread can be preempted in the instructions being modified (no iret to an
 221  * invalid instruction possible) or if the instructions are changed from a
 222  * consistent state to another consistent state atomically.
 223  * More care must be taken when modifying code in the SMP case because of
 224  * Intel's errata. text_poke_smp() takes care that errata, but still
 225  * doesn't support NMI/MCE handler code modifying.
 226  * On the local CPU you need to be protected again NMI or MCE handlers seeing an
 227  * inconsistent instruction while you patch.
 228  */
 229 struct text_poke_param {
 230         void *addr;
 231         const void *opcode;
 232         size_t len;
 233 };
 234
 235 extern void *text_poke(void *addr, const void *opcode, size_t len);
 236 extern void *text_poke_smp(void *addr, const void *opcode, size_t len);
 237 extern void text_poke_smp_batch(struct text_poke_param *params, int n);
 238
 239 #endif /* _ASM_X86_ALTERNATIVE_H */