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 #include <asm/ptrace.h>
   9
  10 /*
  11  * Alternative inline assembly for SMP.
  12  *
  13  * The LOCK_PREFIX macro defined here replaces the LOCK and
  14  * LOCK_PREFIX macros used everywhere in the source tree.
  15  *
  16  * SMP alternatives use the same data structures as the other
  17  * alternatives and the X86_FEATURE_UP flag to indicate the case of a
  18  * UP system running a SMP kernel.  The existing apply_alternatives()
  19  * works fine for patching a SMP kernel for UP.
  20  *
  21  * The SMP alternative tables can be kept after boot and contain both
  22  * UP and SMP versions of the instructions to allow switching back to
  23  * SMP at runtime, when hotplugging in a new CPU, which is especially
  24  * useful in virtualized environments.
  25  *
  26  * The very common lock prefix is handled as special case in a
  27  * separate table which is a pure address list without replacement ptr
  28  * and size information.  That keeps the table sizes small.
  29  */
  30
  31 #ifdef CONFIG_SMP
  32 #define LOCK_PREFIX_HERE \
  33                 ".pushsection .smp_locks,\"a\"\n"       \
  34                 ".balign 4\n"                           \
  35                 ".long 671f - .\n" /* offset */         \
  36                 ".popsection\n"                         \
  37                 "671:"
  38
  39 #define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
  40
  41 #else /* ! CONFIG_SMP */
  42 #define LOCK_PREFIX_HERE ""
  43 #define LOCK_PREFIX ""
  44 #endif
  45
  46 struct alt_instr {
  47         s32 instr_offset;       /* original instruction */
  48         s32 repl_offset;        /* offset to replacement instruction */
  49         u16 cpuid;              /* cpuid bit set for replacement */
  50         u8  instrlen;           /* length of original instruction */
  51         u8  replacementlen;     /* length of new instruction, <= instrlen */
  52 };
  53
  54 extern void alternative_instructions(void);
  55 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  56
  57 struct module;
  58
  59 #ifdef CONFIG_SMP
  60 extern void alternatives_smp_module_add(struct module *mod, char *name,
  61                                         void *locks, void *locks_end,
  62                                         void *text, void *text_end);
  63 extern void alternatives_smp_module_del(struct module *mod);
  64 extern void alternatives_enable_smp(void);
  65 extern int alternatives_text_reserved(void *start, void *end);
  66 extern bool skip_smp_alternatives;
  67 #else
  68 static inline void alternatives_smp_module_add(struct module *mod, char *name,
  69                                                void *locks, void *locks_end,
  70                                                void *text, void *text_end) {}
  71 static inline void alternatives_smp_module_del(struct module *mod) {}
  72 static inline void alternatives_enable_smp(void) {}
  73 static inline int alternatives_text_reserved(void *start, void *end)
  74 {
  75         return 0;
  76 }
  77 #endif  /* CONFIG_SMP */
  78
  79 #define OLDINSTR(oldinstr)      "661:\n\t" oldinstr "\n662:\n"
  80
  81 #define b_replacement(number)   "663"#number
  82 #define e_replacement(number)   "664"#number
  83
  84 #define alt_slen "662b-661b"
  85 #define alt_rlen(number) e_replacement(number)"f-"b_replacement(number)"f"
  86
  87 #define ALTINSTR_ENTRY(feature, number)                                       \
  88         " .long 661b - .\n"                             /* label           */ \
  89         " .long " b_replacement(number)"f - .\n"        /* new instruction */ \
  90         " .word " __stringify(feature) "\n"             /* feature bit     */ \
  91         " .byte " alt_slen "\n"                         /* source len      */ \
  92         " .byte " alt_rlen(number) "\n"                 /* replacement len */
  93
  94 #define DISCARD_ENTRY(number)                           /* rlen <= slen */    \
  95         " .byte 0xff + (" alt_rlen(number) ") - (" alt_slen ")\n"
  96
  97 #define ALTINSTR_REPLACEMENT(newinstr, feature, number) /* replacement */     \
  98         b_replacement(number)":\n\t" newinstr "\n" e_replacement(number) ":\n\t"
  99
 100 /* alternative assembly primitive: */
 101 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
 102         OLDINSTR(oldinstr)                                              \
 103         ".pushsection .altinstructions,\"a\"\n"                         \
 104         ALTINSTR_ENTRY(feature, 1)                                      \
 105         ".popsection\n"                                                 \
 106         ".pushsection .discard,\"aw\",@progbits\n"                      \
 107         DISCARD_ENTRY(1)                                                \
 108         ".popsection\n"                                                 \
 109         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 110         ALTINSTR_REPLACEMENT(newinstr, feature, 1)                      \
 111         ".popsection"
 112
 113 #define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
 114         OLDINSTR(oldinstr)                                              \
 115         ".pushsection .altinstructions,\"a\"\n"                         \
 116         ALTINSTR_ENTRY(feature1, 1)                                     \
 117         ALTINSTR_ENTRY(feature2, 2)                                     \
 118         ".popsection\n"                                                 \
 119         ".pushsection .discard,\"aw\",@progbits\n"                      \
 120         DISCARD_ENTRY(1)                                                \
 121         DISCARD_ENTRY(2)                                                \
 122         ".popsection\n"                                                 \
 123         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 124         ALTINSTR_REPLACEMENT(newinstr1, feature1, 1)                    \
 125         ALTINSTR_REPLACEMENT(newinstr2, feature2, 2)                    \
 126         ".popsection"
 127
 128 /*
 129  * This must be included *after* the definition of ALTERNATIVE due to
 130  * <asm/arch_hweight.h>
 131  */
 132 #include <asm/cpufeature.h>
 133
 134 /*
 135  * Alternative instructions for different CPU types or capabilities.
 136  *
 137  * This allows to use optimized instructions even on generic binary
 138  * kernels.
 139  *
 140  * length of oldinstr must be longer or equal the length of newinstr
 141  * It can be padded with nops as needed.
 142  *
 143  * For non barrier like inlines please define new variants
 144  * without volatile and memory clobber.
 145  */
 146 #define alternative(oldinstr, newinstr, feature)                        \
 147         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 148
 149 /*
 150  * Alternative inline assembly with input.
 151  *
 152  * Pecularities:
 153  * No memory clobber here.
 154  * Argument numbers start with 1.
 155  * Best is to use constraints that are fixed size (like (%1) ... "r")
 156  * If you use variable sized constraints like "m" or "g" in the
 157  * replacement make sure to pad to the worst case length.
 158  * Leaving an unused argument 0 to keep API compatibility.
 159  */
 160 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 161         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 162                 : : "i" (0), ## input)
 163
 164 /* Like alternative_input, but with a single output argument */
 165 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 166         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 167                 : output : "i" (0), ## input)
 168
 169 /* Like alternative_io, but for replacing a direct call with another one. */
 170 #define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 171         asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 172                 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 173
 174 /*
 175  * Like alternative_call, but there are two features and respective functions.
 176  * If CPU has feature2, function2 is used.
 177  * Otherwise, if CPU has feature1, function1 is used.
 178  * Otherwise, old function is used.
 179  */
 180 #define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
 181                            output, input...)                                  \
 182         asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
 183                 "call %P[new2]", feature2)                                    \
 184                 : output : [old] "i" (oldfunc), [new1] "i" (newfunc1),        \
 185                 [new2] "i" (newfunc2), ## input)
 186
 187 /*
 188  * use this macro(s) if you need more than one output parameter
 189  * in alternative_io
 190  */
 191 #define ASM_OUTPUT2(a...) a
 192
 193 /*
 194  * use this macro if you need clobbers but no inputs in
 195  * alternative_{input,io,call}()
 196  */
 197 #define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
 198
 199 struct paravirt_patch_site;
 200 #ifdef CONFIG_PARAVIRT
 201 void apply_paravirt(struct paravirt_patch_site *start,
 202                     struct paravirt_patch_site *end);
 203 #else
 204 static inline void apply_paravirt(struct paravirt_patch_site *start,
 205                                   struct paravirt_patch_site *end)
 206 {}
 207 #define __parainstructions      NULL
 208 #define __parainstructions_end  NULL
 209 #endif
 210
 211 extern void *text_poke_early(void *addr, const void *opcode, size_t len);
 212
 213 /*
 214  * Clear and restore the kernel write-protection flag on the local CPU.
 215  * Allows the kernel to edit read-only pages.
 216  * Side-effect: any interrupt handler running between save and restore will have
 217  * the ability to write to read-only pages.
 218  *
 219  * Warning:
 220  * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
 221  * no thread can be preempted in the instructions being modified (no iret to an
 222  * invalid instruction possible) or if the instructions are changed from a
 223  * consistent state to another consistent state atomically.
 224  * On the local CPU you need to be protected again NMI or MCE handlers seeing an
 225  * inconsistent instruction while you patch.
 226  */
 227 extern void *text_poke(void *addr, const void *opcode, size_t len);
 228 extern int poke_int3_handler(struct pt_regs *regs);
 229 extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
 230
 231 #endif /* _ASM_X86_ALTERNATIVE_H */