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 struct alt_instr {
  49         s32 instr_offset;       /* original instruction */
  50         s32 repl_offset;        /* offset to replacement instruction */
  51         u16 cpuid;              /* cpuid bit set for replacement */
  52         u8  instrlen;           /* length of original instruction */
  53         u8  replacementlen;     /* length of new instruction */
  54         u8  padlen;             /* length of build-time padding */
  55 } __packed;
  56
  57 /*
  58  * Debug flag that can be tested to see whether alternative
  59  * instructions were patched in already:
  60  */
  61 extern int alternatives_patched;
  62
  63 extern void alternative_instructions(void);
  64 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  65
  66 struct module;
  67
  68 #ifdef CONFIG_SMP
  69 extern void alternatives_smp_module_add(struct module *mod, char *name,
  70                                         void *locks, void *locks_end,
  71                                         void *text, void *text_end);
  72 extern void alternatives_smp_module_del(struct module *mod);
  73 extern void alternatives_enable_smp(void);
  74 extern int alternatives_text_reserved(void *start, void *end);
  75 extern bool skip_smp_alternatives;
  76 #else
  77 static inline void alternatives_smp_module_add(struct module *mod, char *name,
  78                                                void *locks, void *locks_end,
  79                                                void *text, void *text_end) {}
  80 static inline void alternatives_smp_module_del(struct module *mod) {}
  81 static inline void alternatives_enable_smp(void) {}
  82 static inline int alternatives_text_reserved(void *start, void *end)
  83 {
  84         return 0;
  85 }
  86 #endif  /* CONFIG_SMP */
  87
  88 #define b_replacement(num)      "664"#num
  89 #define e_replacement(num)      "665"#num
  90
  91 #define alt_end_marker          "663"
  92 #define alt_slen                "662b-661b"
  93 #define alt_pad_len             alt_end_marker"b-662b"
  94 #define alt_total_slen          alt_end_marker"b-661b"
  95 #define alt_rlen(num)           e_replacement(num)"f-"b_replacement(num)"f"
  96
  97 #define __OLDINSTR(oldinstr, num)                                       \
  98         "661:\n\t" oldinstr "\n662:\n"                                  \
  99         ".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * "          \
 100                 "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n"
 101
 102 #define OLDINSTR(oldinstr, num)                                         \
 103         __OLDINSTR(oldinstr, num)                                       \
 104         alt_end_marker ":\n"
 105
 106 /*
 107  * gas compatible max based on the idea from:
 108  * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
 109  *
 110  * The additional "-" is needed because gas uses a "true" value of -1.
 111  */
 112 #define alt_max_short(a, b)     "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"
 113
 114 /*
 115  * Pad the second replacement alternative with additional NOPs if it is
 116  * additionally longer than the first replacement alternative.
 117  */
 118 #define OLDINSTR_2(oldinstr, num1, num2) \
 119         "661:\n\t" oldinstr "\n662:\n"                                                          \
 120         ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * "  \
 121                 "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n"  \
 122         alt_end_marker ":\n"
 123
 124 #define ALTINSTR_ENTRY(feature, num)                                          \
 125         " .long 661b - .\n"                             /* label           */ \
 126         " .long " b_replacement(num)"f - .\n"           /* new instruction */ \
 127         " .word " __stringify(feature) "\n"             /* feature bit     */ \
 128         " .byte " alt_total_slen "\n"                   /* source len      */ \
 129         " .byte " alt_rlen(num) "\n"                    /* replacement len */ \
 130         " .byte " alt_pad_len "\n"                      /* pad len */
 131
 132 #define ALTINSTR_REPLACEMENT(newinstr, feature, num)    /* replacement */     \
 133         b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t"
 134
 135 /* alternative assembly primitive: */
 136 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
 137         OLDINSTR(oldinstr, 1)                                           \
 138         ".pushsection .altinstructions,\"a\"\n"                         \
 139         ALTINSTR_ENTRY(feature, 1)                                      \
 140         ".popsection\n"                                                 \
 141         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 142         ALTINSTR_REPLACEMENT(newinstr, feature, 1)                      \
 143         ".popsection\n"
 144
 145 #define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
 146         OLDINSTR_2(oldinstr, 1, 2)                                      \
 147         ".pushsection .altinstructions,\"a\"\n"                         \
 148         ALTINSTR_ENTRY(feature1, 1)                                     \
 149         ALTINSTR_ENTRY(feature2, 2)                                     \
 150         ".popsection\n"                                                 \
 151         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 152         ALTINSTR_REPLACEMENT(newinstr1, feature1, 1)                    \
 153         ALTINSTR_REPLACEMENT(newinstr2, feature2, 2)                    \
 154         ".popsection\n"
 155
 156 /*
 157  * Alternative instructions for different CPU types or capabilities.
 158  *
 159  * This allows to use optimized instructions even on generic binary
 160  * kernels.
 161  *
 162  * length of oldinstr must be longer or equal the length of newinstr
 163  * It can be padded with nops as needed.
 164  *
 165  * For non barrier like inlines please define new variants
 166  * without volatile and memory clobber.
 167  */
 168 #define alternative(oldinstr, newinstr, feature)                        \
 169         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 170
 171 #define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
 172         asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
 173
 174 /*
 175  * Alternative inline assembly with input.
 176  *
 177  * Pecularities:
 178  * No memory clobber here.
 179  * Argument numbers start with 1.
 180  * Best is to use constraints that are fixed size (like (%1) ... "r")
 181  * If you use variable sized constraints like "m" or "g" in the
 182  * replacement make sure to pad to the worst case length.
 183  * Leaving an unused argument 0 to keep API compatibility.
 184  */
 185 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 186         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 187                 : : "i" (0), ## input)
 188
 189 /*
 190  * This is similar to alternative_input. But it has two features and
 191  * respective instructions.
 192  *
 193  * If CPU has feature2, newinstr2 is used.
 194  * Otherwise, if CPU has feature1, newinstr1 is used.
 195  * Otherwise, oldinstr is used.
 196  */
 197 #define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2,        \
 198                            feature2, input...)                               \
 199         asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1,            \
 200                 newinstr2, feature2)                                         \
 201                 : : "i" (0), ## input)
 202
 203 /* Like alternative_input, but with a single output argument */
 204 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 205         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 206                 : output : "i" (0), ## input)
 207
 208 /* Like alternative_io, but for replacing a direct call with another one. */
 209 #define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 210         asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 211                 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 212
 213 /*
 214  * Like alternative_call, but there are two features and respective functions.
 215  * If CPU has feature2, function2 is used.
 216  * Otherwise, if CPU has feature1, function1 is used.
 217  * Otherwise, old function is used.
 218  */
 219 #define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
 220                            output, input...)                                  \
 221 {                                                                             \
 222         asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
 223                 "call %P[new2]", feature2)                                    \
 224                 : output, ASM_CALL_CONSTRAINT                                 \
 225                 : [old] "i" (oldfunc), [new1] "i" (newfunc1),                 \
 226                   [new2] "i" (newfunc2), ## input);                           \
 227 }
 228
 229 /*
 230  * use this macro(s) if you need more than one output parameter
 231  * in alternative_io
 232  */
 233 #define ASM_OUTPUT2(a...) a
 234
 235 /*
 236  * use this macro if you need clobbers but no inputs in
 237  * alternative_{input,io,call}()
 238  */
 239 #define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
 240
 241 #endif /* __ASSEMBLY__ */
 242
 243 #endif /* _ASM_X86_ALTERNATIVE_H */