arch/x86/include/asm/alternative.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _ASM_X86_ALTERNATIVE_H
   3 #define _ASM_X86_ALTERNATIVE_H
   4
   5 #ifndef __ASSEMBLY__
   6
   7 #include <linux/types.h>
   8 #include <linux/stddef.h>
   9 #include <linux/stringify.h>
  10 #include <asm/asm.h>
  11
  12 /*
  13  * Alternative inline assembly for SMP.
  14  *
  15  * The LOCK_PREFIX macro defined here replaces the LOCK and
  16  * LOCK_PREFIX macros used everywhere in the source tree.
  17  *
  18  * SMP alternatives use the same data structures as the other
  19  * alternatives and the X86_FEATURE_UP flag to indicate the case of a
  20  * UP system running a SMP kernel.  The existing apply_alternatives()
  21  * works fine for patching a SMP kernel for UP.
  22  *
  23  * The SMP alternative tables can be kept after boot and contain both
  24  * UP and SMP versions of the instructions to allow switching back to
  25  * SMP at runtime, when hotplugging in a new CPU, which is especially
  26  * useful in virtualized environments.
  27  *
  28  * The very common lock prefix is handled as special case in a
  29  * separate table which is a pure address list without replacement ptr
  30  * and size information.  That keeps the table sizes small.
  31  */
  32
  33 #ifdef CONFIG_SMP
  34 #define LOCK_PREFIX_HERE \
  35                 ".pushsection .smp_locks,\"a\"\n"       \
  36                 ".balign 4\n"                           \
  37                 ".long 671f - .\n" /* offset */         \
  38                 ".popsection\n"                         \
  39                 "671:"
  40
  41 #define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
  42
  43 #else /* ! CONFIG_SMP */
  44 #define LOCK_PREFIX_HERE ""
  45 #define LOCK_PREFIX ""
  46 #endif
  47
  48 /*
  49  * objtool annotation to ignore the alternatives and only consider the original
  50  * instruction(s).
  51  */
  52 #define ANNOTATE_IGNORE_ALTERNATIVE                             \
  53         "999:\n\t"                                              \
  54         ".pushsection .discard.ignore_alts\n\t"                 \
  55         ".long 999b - .\n\t"                                    \
  56         ".popsection\n\t"
  57
  58 struct alt_instr {
  59         s32 instr_offset;       /* original instruction */
  60         s32 repl_offset;        /* offset to replacement instruction */
  61         u16 cpuid;              /* cpuid bit set for replacement */
  62         u8  instrlen;           /* length of original instruction */
  63         u8  replacementlen;     /* length of new instruction */
  64         u8  padlen;             /* length of build-time padding */
  65 } __packed;
  66
  67 /*
  68  * Debug flag that can be tested to see whether alternative
  69  * instructions were patched in already:
  70  */
  71 extern int alternatives_patched;
  72
  73 extern void alternative_instructions(void);
  74 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  75
  76 struct module;
  77
  78 #ifdef CONFIG_SMP
  79 extern void alternatives_smp_module_add(struct module *mod, char *name,
  80                                         void *locks, void *locks_end,
  81                                         void *text, void *text_end);
  82 extern void alternatives_smp_module_del(struct module *mod);
  83 extern void alternatives_enable_smp(void);
  84 extern int alternatives_text_reserved(void *start, void *end);
  85 extern bool skip_smp_alternatives;
  86 #else
  87 static inline void alternatives_smp_module_add(struct module *mod, char *name,
  88                                                void *locks, void *locks_end,
  89                                                void *text, void *text_end) {}
  90 static inline void alternatives_smp_module_del(struct module *mod) {}
  91 static inline void alternatives_enable_smp(void) {}
  92 static inline int alternatives_text_reserved(void *start, void *end)
  93 {
  94         return 0;
  95 }
  96 #endif  /* CONFIG_SMP */
  97
  98 #define b_replacement(num)      "664"#num
  99 #define e_replacement(num)      "665"#num
 100
 101 #define alt_end_marker          "663"
 102 #define alt_slen                "662b-661b"
 103 #define alt_pad_len             alt_end_marker"b-662b"
 104 #define alt_total_slen          alt_end_marker"b-661b"
 105 #define alt_rlen(num)           e_replacement(num)"f-"b_replacement(num)"f"
 106
 107 #define OLDINSTR(oldinstr, num)                                         \
 108         "# ALT: oldnstr\n"                                              \
 109         "661:\n\t" oldinstr "\n662:\n"                                  \
 110         "# ALT: padding\n"                                              \
 111         ".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * "          \
 112                 "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n"           \
 113         alt_end_marker ":\n"
 114
 115 /*
 116  * gas compatible max based on the idea from:
 117  * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
 118  *
 119  * The additional "-" is needed because gas uses a "true" value of -1.
 120  */
 121 #define alt_max_short(a, b)     "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"
 122
 123 /*
 124  * Pad the second replacement alternative with additional NOPs if it is
 125  * additionally longer than the first replacement alternative.
 126  */
 127 #define OLDINSTR_2(oldinstr, num1, num2) \
 128         "# ALT: oldinstr2\n"                                                                    \
 129         "661:\n\t" oldinstr "\n662:\n"                                                          \
 130         "# ALT: padding2\n"                                                                     \
 131         ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * "  \
 132                 "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n"  \
 133         alt_end_marker ":\n"
 134
 135 #define OLDINSTR_3(oldinsn, n1, n2, n3)                                                         \
 136         "# ALT: oldinstr3\n"                                                                    \
 137         "661:\n\t" oldinsn "\n662:\n"                                                           \
 138         "# ALT: padding3\n"                                                                     \
 139         ".skip -((" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3))      \
 140                 " - (" alt_slen ")) > 0) * "                                                    \
 141                 "(" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3))      \
 142                 " - (" alt_slen ")), 0x90\n"                                                    \
 143         alt_end_marker ":\n"
 144
 145 #define ALTINSTR_ENTRY(feature, num)                                          \
 146         " .long 661b - .\n"                             /* label           */ \
 147         " .long " b_replacement(num)"f - .\n"           /* new instruction */ \
 148         " .word " __stringify(feature) "\n"             /* feature bit     */ \
 149         " .byte " alt_total_slen "\n"                   /* source len      */ \
 150         " .byte " alt_rlen(num) "\n"                    /* replacement len */ \
 151         " .byte " alt_pad_len "\n"                      /* pad len */
 152
 153 #define ALTINSTR_REPLACEMENT(newinstr, feature, num)    /* replacement */       \
 154         "# ALT: replacement " #num "\n"                                         \
 155         b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n"
 156
 157 /* alternative assembly primitive: */
 158 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
 159         OLDINSTR(oldinstr, 1)                                           \
 160         ".pushsection .altinstructions,\"a\"\n"                         \
 161         ALTINSTR_ENTRY(feature, 1)                                      \
 162         ".popsection\n"                                                 \
 163         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 164         ALTINSTR_REPLACEMENT(newinstr, feature, 1)                      \
 165         ".popsection\n"
 166
 167 #define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
 168         OLDINSTR_2(oldinstr, 1, 2)                                      \
 169         ".pushsection .altinstructions,\"a\"\n"                         \
 170         ALTINSTR_ENTRY(feature1, 1)                                     \
 171         ALTINSTR_ENTRY(feature2, 2)                                     \
 172         ".popsection\n"                                                 \
 173         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 174         ALTINSTR_REPLACEMENT(newinstr1, feature1, 1)                    \
 175         ALTINSTR_REPLACEMENT(newinstr2, feature2, 2)                    \
 176         ".popsection\n"
 177
 178 #define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \
 179         OLDINSTR_3(oldinsn, 1, 2, 3)                                            \
 180         ".pushsection .altinstructions,\"a\"\n"                                 \
 181         ALTINSTR_ENTRY(feat1, 1)                                                \
 182         ALTINSTR_ENTRY(feat2, 2)                                                \
 183         ALTINSTR_ENTRY(feat3, 3)                                                \
 184         ".popsection\n"                                                         \
 185         ".pushsection .altinstr_replacement, \"ax\"\n"                          \
 186         ALTINSTR_REPLACEMENT(newinsn1, feat1, 1)                                \
 187         ALTINSTR_REPLACEMENT(newinsn2, feat2, 2)                                \
 188         ALTINSTR_REPLACEMENT(newinsn3, feat3, 3)                                \
 189         ".popsection\n"
 190
 191 /*
 192  * Alternative instructions for different CPU types or capabilities.
 193  *
 194  * This allows to use optimized instructions even on generic binary
 195  * kernels.
 196  *
 197  * length of oldinstr must be longer or equal the length of newinstr
 198  * It can be padded with nops as needed.
 199  *
 200  * For non barrier like inlines please define new variants
 201  * without volatile and memory clobber.
 202  */
 203 #define alternative(oldinstr, newinstr, feature)                        \
 204         asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 205
 206 #define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
 207         asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
 208
 209 /*
 210  * Alternative inline assembly with input.
 211  *
 212  * Peculiarities:
 213  * No memory clobber here.
 214  * Argument numbers start with 1.
 215  * Best is to use constraints that are fixed size (like (%1) ... "r")
 216  * If you use variable sized constraints like "m" or "g" in the
 217  * replacement make sure to pad to the worst case length.
 218  * Leaving an unused argument 0 to keep API compatibility.
 219  */
 220 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 221         asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature)   \
 222                 : : "i" (0), ## input)
 223
 224 /*
 225  * This is similar to alternative_input. But it has two features and
 226  * respective instructions.
 227  *
 228  * If CPU has feature2, newinstr2 is used.
 229  * Otherwise, if CPU has feature1, newinstr1 is used.
 230  * Otherwise, oldinstr is used.
 231  */
 232 #define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2,        \
 233                            feature2, input...)                               \
 234         asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1,     \
 235                 newinstr2, feature2)                                         \
 236                 : : "i" (0), ## input)
 237
 238 /* Like alternative_input, but with a single output argument */
 239 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 240         asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature)   \
 241                 : output : "i" (0), ## input)
 242
 243 /* Like alternative_io, but for replacing a direct call with another one. */
 244 #define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 245         asm_inline volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 246                 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 247
 248 /*
 249  * Like alternative_call, but there are two features and respective functions.
 250  * If CPU has feature2, function2 is used.
 251  * Otherwise, if CPU has feature1, function1 is used.
 252  * Otherwise, old function is used.
 253  */
 254 #define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
 255                            output, input...)                                  \
 256         asm_inline volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
 257                 "call %P[new2]", feature2)                                    \
 258                 : output, ASM_CALL_CONSTRAINT                                 \
 259                 : [old] "i" (oldfunc), [new1] "i" (newfunc1),                 \
 260                   [new2] "i" (newfunc2), ## input)
 261
 262 /*
 263  * use this macro(s) if you need more than one output parameter
 264  * in alternative_io
 265  */
 266 #define ASM_OUTPUT2(a...) a
 267
 268 /*
 269  * use this macro if you need clobbers but no inputs in
 270  * alternative_{input,io,call}()
 271  */
 272 #define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
 273
 274 #endif /* __ASSEMBLY__ */
 275
 276 #endif /* _ASM_X86_ALTERNATIVE_H */