linux/arch/x86/include/asm/alternative.h
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   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef _ASM_X86_ALTERNATIVE_H
   3#define _ASM_X86_ALTERNATIVE_H
   4
   5#include <linux/types.h>
   6#include <linux/stringify.h>
   7#include <asm/asm.h>
   8
   9#define ALTINSTR_FLAG_INV       (1 << 15)
  10#define ALT_NOT(feat)           ((feat) | ALTINSTR_FLAG_INV)
  11
  12#ifndef __ASSEMBLY__
  13
  14#include <linux/stddef.h>
  15
  16/*
  17 * Alternative inline assembly for SMP.
  18 *
  19 * The LOCK_PREFIX macro defined here replaces the LOCK and
  20 * LOCK_PREFIX macros used everywhere in the source tree.
  21 *
  22 * SMP alternatives use the same data structures as the other
  23 * alternatives and the X86_FEATURE_UP flag to indicate the case of a
  24 * UP system running a SMP kernel.  The existing apply_alternatives()
  25 * works fine for patching a SMP kernel for UP.
  26 *
  27 * The SMP alternative tables can be kept after boot and contain both
  28 * UP and SMP versions of the instructions to allow switching back to
  29 * SMP at runtime, when hotplugging in a new CPU, which is especially
  30 * useful in virtualized environments.
  31 *
  32 * The very common lock prefix is handled as special case in a
  33 * separate table which is a pure address list without replacement ptr
  34 * and size information.  That keeps the table sizes small.
  35 */
  36
  37#ifdef CONFIG_SMP
  38#define LOCK_PREFIX_HERE \
  39                ".pushsection .smp_locks,\"a\"\n"       \
  40                ".balign 4\n"                           \
  41                ".long 671f - .\n" /* offset */         \
  42                ".popsection\n"                         \
  43                "671:"
  44
  45#define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
  46
  47#else /* ! CONFIG_SMP */
  48#define LOCK_PREFIX_HERE ""
  49#define LOCK_PREFIX ""
  50#endif
  51
  52/*
  53 * objtool annotation to ignore the alternatives and only consider the original
  54 * instruction(s).
  55 */
  56#define ANNOTATE_IGNORE_ALTERNATIVE                             \
  57        "999:\n\t"                                              \
  58        ".pushsection .discard.ignore_alts\n\t"                 \
  59        ".long 999b - .\n\t"                                    \
  60        ".popsection\n\t"
  61
  62struct alt_instr {
  63        s32 instr_offset;       /* original instruction */
  64        s32 repl_offset;        /* offset to replacement instruction */
  65        u16 cpuid;              /* cpuid bit set for replacement */
  66        u8  instrlen;           /* length of original instruction */
  67        u8  replacementlen;     /* length of new instruction */
  68} __packed;
  69
  70/*
  71 * Debug flag that can be tested to see whether alternative
  72 * instructions were patched in already:
  73 */
  74extern int alternatives_patched;
  75
  76extern void alternative_instructions(void);
  77extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  78
  79struct module;
  80
  81#ifdef CONFIG_SMP
  82extern void alternatives_smp_module_add(struct module *mod, char *name,
  83                                        void *locks, void *locks_end,
  84                                        void *text, void *text_end);
  85extern void alternatives_smp_module_del(struct module *mod);
  86extern void alternatives_enable_smp(void);
  87extern int alternatives_text_reserved(void *start, void *end);
  88extern bool skip_smp_alternatives;
  89#else
  90static inline void alternatives_smp_module_add(struct module *mod, char *name,
  91                                               void *locks, void *locks_end,
  92                                               void *text, void *text_end) {}
  93static inline void alternatives_smp_module_del(struct module *mod) {}
  94static inline void alternatives_enable_smp(void) {}
  95static inline int alternatives_text_reserved(void *start, void *end)
  96{
  97        return 0;
  98}
  99#endif  /* CONFIG_SMP */
 100
 101#define b_replacement(num)      "664"#num
 102#define e_replacement(num)      "665"#num
 103
 104#define alt_end_marker          "663"
 105#define alt_slen                "662b-661b"
 106#define alt_total_slen          alt_end_marker"b-661b"
 107#define alt_rlen(num)           e_replacement(num)"f-"b_replacement(num)"f"
 108
 109#define OLDINSTR(oldinstr, num)                                         \
 110        "# ALT: oldnstr\n"                                              \
 111        "661:\n\t" oldinstr "\n662:\n"                                  \
 112        "# ALT: padding\n"                                              \
 113        ".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * "          \
 114                "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n"           \
 115        alt_end_marker ":\n"
 116
 117/*
 118 * gas compatible max based on the idea from:
 119 * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
 120 *
 121 * The additional "-" is needed because gas uses a "true" value of -1.
 122 */
 123#define alt_max_short(a, b)     "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"
 124
 125/*
 126 * Pad the second replacement alternative with additional NOPs if it is
 127 * additionally longer than the first replacement alternative.
 128 */
 129#define OLDINSTR_2(oldinstr, num1, num2) \
 130        "# ALT: oldinstr2\n"                                                                    \
 131        "661:\n\t" oldinstr "\n662:\n"                                                          \
 132        "# ALT: padding2\n"                                                                     \
 133        ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * "  \
 134                "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n"  \
 135        alt_end_marker ":\n"
 136
 137#define OLDINSTR_3(oldinsn, n1, n2, n3)                                                         \
 138        "# ALT: oldinstr3\n"                                                                    \
 139        "661:\n\t" oldinsn "\n662:\n"                                                           \
 140        "# ALT: padding3\n"                                                                     \
 141        ".skip -((" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3))      \
 142                " - (" alt_slen ")) > 0) * "                                                    \
 143                "(" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3))      \
 144                " - (" alt_slen ")), 0x90\n"                                                    \
 145        alt_end_marker ":\n"
 146
 147#define ALTINSTR_ENTRY(feature, num)                                          \
 148        " .long 661b - .\n"                             /* label           */ \
 149        " .long " b_replacement(num)"f - .\n"           /* new instruction */ \
 150        " .word " __stringify(feature) "\n"             /* feature bit     */ \
 151        " .byte " alt_total_slen "\n"                   /* source len      */ \
 152        " .byte " alt_rlen(num) "\n"                    /* replacement len */
 153
 154#define ALTINSTR_REPLACEMENT(newinstr, num)             /* replacement */       \
 155        "# ALT: replacement " #num "\n"                                         \
 156        b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n"
 157
 158/* alternative assembly primitive: */
 159#define ALTERNATIVE(oldinstr, newinstr, feature)                        \
 160        OLDINSTR(oldinstr, 1)                                           \
 161        ".pushsection .altinstructions,\"a\"\n"                         \
 162        ALTINSTR_ENTRY(feature, 1)                                      \
 163        ".popsection\n"                                                 \
 164        ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 165        ALTINSTR_REPLACEMENT(newinstr, 1)                               \
 166        ".popsection\n"
 167
 168#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
 169        OLDINSTR_2(oldinstr, 1, 2)                                      \
 170        ".pushsection .altinstructions,\"a\"\n"                         \
 171        ALTINSTR_ENTRY(feature1, 1)                                     \
 172        ALTINSTR_ENTRY(feature2, 2)                                     \
 173        ".popsection\n"                                                 \
 174        ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 175        ALTINSTR_REPLACEMENT(newinstr1, 1)                              \
 176        ALTINSTR_REPLACEMENT(newinstr2, 2)                              \
 177        ".popsection\n"
 178
 179/* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
 180#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr_yes, newinstr_no) \
 181        ALTERNATIVE_2(oldinstr, newinstr_no, X86_FEATURE_ALWAYS,        \
 182                      newinstr_yes, feature)
 183
 184#define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \
 185        OLDINSTR_3(oldinsn, 1, 2, 3)                                            \
 186        ".pushsection .altinstructions,\"a\"\n"                                 \
 187        ALTINSTR_ENTRY(feat1, 1)                                                \
 188        ALTINSTR_ENTRY(feat2, 2)                                                \
 189        ALTINSTR_ENTRY(feat3, 3)                                                \
 190        ".popsection\n"                                                         \
 191        ".pushsection .altinstr_replacement, \"ax\"\n"                          \
 192        ALTINSTR_REPLACEMENT(newinsn1, 1)                                       \
 193        ALTINSTR_REPLACEMENT(newinsn2, 2)                                       \
 194        ALTINSTR_REPLACEMENT(newinsn3, 3)                                       \
 195        ".popsection\n"
 196
 197/*
 198 * Alternative instructions for different CPU types or capabilities.
 199 *
 200 * This allows to use optimized instructions even on generic binary
 201 * kernels.
 202 *
 203 * length of oldinstr must be longer or equal the length of newinstr
 204 * It can be padded with nops as needed.
 205 *
 206 * For non barrier like inlines please define new variants
 207 * without volatile and memory clobber.
 208 */
 209#define alternative(oldinstr, newinstr, feature)                        \
 210        asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 211
 212#define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
 213        asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
 214
 215#define alternative_ternary(oldinstr, feature, newinstr_yes, newinstr_no) \
 216        asm_inline volatile(ALTERNATIVE_TERNARY(oldinstr, feature, newinstr_yes, newinstr_no) ::: "memory")
 217
 218/*
 219 * Alternative inline assembly with input.
 220 *
 221 * Peculiarities:
 222 * No memory clobber here.
 223 * Argument numbers start with 1.
 224 * Leaving an unused argument 0 to keep API compatibility.
 225 */
 226#define alternative_input(oldinstr, newinstr, feature, input...)        \
 227        asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature)   \
 228                : : "i" (0), ## input)
 229
 230/*
 231 * This is similar to alternative_input. But it has two features and
 232 * respective instructions.
 233 *
 234 * If CPU has feature2, newinstr2 is used.
 235 * Otherwise, if CPU has feature1, newinstr1 is used.
 236 * Otherwise, oldinstr is used.
 237 */
 238#define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2,        \
 239                           feature2, input...)                               \
 240        asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1,     \
 241                newinstr2, feature2)                                         \
 242                : : "i" (0), ## input)
 243
 244/* Like alternative_input, but with a single output argument */
 245#define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 246        asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature)   \
 247                : output : "i" (0), ## input)
 248
 249/* Like alternative_io, but for replacing a direct call with another one. */
 250#define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 251        asm_inline volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 252                : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 253
 254/*
 255 * Like alternative_call, but there are two features and respective functions.
 256 * If CPU has feature2, function2 is used.
 257 * Otherwise, if CPU has feature1, function1 is used.
 258 * Otherwise, old function is used.
 259 */
 260#define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
 261                           output, input...)                                  \
 262        asm_inline volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
 263                "call %P[new2]", feature2)                                    \
 264                : output, ASM_CALL_CONSTRAINT                                 \
 265                : [old] "i" (oldfunc), [new1] "i" (newfunc1),                 \
 266                  [new2] "i" (newfunc2), ## input)
 267
 268/*
 269 * use this macro(s) if you need more than one output parameter
 270 * in alternative_io
 271 */
 272#define ASM_OUTPUT2(a...) a
 273
 274/*
 275 * use this macro if you need clobbers but no inputs in
 276 * alternative_{input,io,call}()
 277 */
 278#define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
 279
 280#else /* __ASSEMBLY__ */
 281
 282#ifdef CONFIG_SMP
 283        .macro LOCK_PREFIX
 284672:    lock
 285        .pushsection .smp_locks,"a"
 286        .balign 4
 287        .long 672b - .
 288        .popsection
 289        .endm
 290#else
 291        .macro LOCK_PREFIX
 292        .endm
 293#endif
 294
 295/*
 296 * objtool annotation to ignore the alternatives and only consider the original
 297 * instruction(s).
 298 */
 299.macro ANNOTATE_IGNORE_ALTERNATIVE
 300        .Lannotate_\@:
 301        .pushsection .discard.ignore_alts
 302        .long .Lannotate_\@ - .
 303        .popsection
 304.endm
 305
 306/*
 307 * Issue one struct alt_instr descriptor entry (need to put it into
 308 * the section .altinstructions, see below). This entry contains
 309 * enough information for the alternatives patching code to patch an
 310 * instruction. See apply_alternatives().
 311 */
 312.macro altinstruction_entry orig alt feature orig_len alt_len
 313        .long \orig - .
 314        .long \alt - .
 315        .word \feature
 316        .byte \orig_len
 317        .byte \alt_len
 318.endm
 319
 320/*
 321 * Define an alternative between two instructions. If @feature is
 322 * present, early code in apply_alternatives() replaces @oldinstr with
 323 * @newinstr. ".skip" directive takes care of proper instruction padding
 324 * in case @newinstr is longer than @oldinstr.
 325 */
 326.macro ALTERNATIVE oldinstr, newinstr, feature
 327140:
 328        \oldinstr
 329141:
 330        .skip -(((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)),0x90
 331142:
 332
 333        .pushsection .altinstructions,"a"
 334        altinstruction_entry 140b,143f,\feature,142b-140b,144f-143f
 335        .popsection
 336
 337        .pushsection .altinstr_replacement,"ax"
 338143:
 339        \newinstr
 340144:
 341        .popsection
 342.endm
 343
 344#define old_len                 141b-140b
 345#define new_len1                144f-143f
 346#define new_len2                145f-144f
 347
 348/*
 349 * gas compatible max based on the idea from:
 350 * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
 351 *
 352 * The additional "-" is needed because gas uses a "true" value of -1.
 353 */
 354#define alt_max_short(a, b)     ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
 355
 356
 357/*
 358 * Same as ALTERNATIVE macro above but for two alternatives. If CPU
 359 * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
 360 * @feature2, it replaces @oldinstr with @feature2.
 361 */
 362.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
 363140:
 364        \oldinstr
 365141:
 366        .skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
 367                (alt_max_short(new_len1, new_len2) - (old_len)),0x90
 368142:
 369
 370        .pushsection .altinstructions,"a"
 371        altinstruction_entry 140b,143f,\feature1,142b-140b,144f-143f
 372        altinstruction_entry 140b,144f,\feature2,142b-140b,145f-144f
 373        .popsection
 374
 375        .pushsection .altinstr_replacement,"ax"
 376143:
 377        \newinstr1
 378144:
 379        \newinstr2
 380145:
 381        .popsection
 382.endm
 383
 384/* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
 385#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr_yes, newinstr_no) \
 386        ALTERNATIVE_2 oldinstr, newinstr_no, X86_FEATURE_ALWAYS,        \
 387        newinstr_yes, feature
 388
 389#endif /* __ASSEMBLY__ */
 390
 391#endif /* _ASM_X86_ALTERNATIVE_H */
 392
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