LXR linux/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
  58struct 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 */
  71extern int alternatives_patched;
  72
  73extern void alternative_instructions(void);
  74extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  75
  76struct module;
  77
  78#ifdef CONFIG_SMP
  79extern void alternatives_smp_module_add(struct module *mod, char *name,
  80                                        void *locks, void *locks_end,
  81                                        void *text, void *text_end);
  82extern void alternatives_smp_module_del(struct module *mod);
  83extern void alternatives_enable_smp(void);
  84extern int alternatives_text_reserved(void *start, void *end);
  85extern bool skip_smp_alternatives;
  86#else
  87static inline void alternatives_smp_module_add(struct module *mod, char *name,
  88                                               void *locks, void *locks_end,
  89                                               void *text, void *text_end) {}
  90static inline void alternatives_smp_module_del(struct module *mod) {}
  91static inline void alternatives_enable_smp(void) {}
  92static 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 */
 277