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 */