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 
9 /*
10  * Alternative inline assembly for SMP.
11  *
12  * The LOCK_PREFIX macro defined here replaces the LOCK and
13  * LOCK_PREFIX macros used everywhere in the source tree.
14  *
15  * SMP alternatives use the same data structures as the other
16  * alternatives and the X86_FEATURE_UP flag to indicate the case of a
17  * UP system running a SMP kernel.  The existing apply_alternatives()
18  * works fine for patching a SMP kernel for UP.
19  *
20  * The SMP alternative tables can be kept after boot and contain both
21  * UP and SMP versions of the instructions to allow switching back to
22  * SMP at runtime, when hotplugging in a new CPU, which is especially
23  * useful in virtualized environments.
24  *
25  * The very common lock prefix is handled as special case in a
26  * separate table which is a pure address list without replacement ptr
27  * and size information.  That keeps the table sizes small.
28  */
29 
30 #ifdef CONFIG_SMP
31 #define LOCK_PREFIX_HERE \
32 		".section .smp_locks,\"a\"\n"	\
33 		".balign 4\n"			\
34 		".long 671f - .\n" /* offset */	\
35 		".previous\n"			\
36 		"671:"
37 
38 #define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
39 
40 #else /* ! CONFIG_SMP */
41 #define LOCK_PREFIX_HERE ""
42 #define LOCK_PREFIX ""
43 #endif
44 
45 struct alt_instr {
46 	s32 instr_offset;	/* original instruction */
47 	s32 repl_offset;	/* offset to replacement instruction */
48 	u16 cpuid;		/* cpuid bit set for replacement */
49 	u8  instrlen;		/* length of original instruction */
50 	u8  replacementlen;	/* length of new instruction, <= instrlen */
51 };
52 
53 extern void alternative_instructions(void);
54 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
55 
56 struct module;
57 
58 #ifdef CONFIG_SMP
59 extern void alternatives_smp_module_add(struct module *mod, char *name,
60 					void *locks, void *locks_end,
61 					void *text, void *text_end);
62 extern void alternatives_smp_module_del(struct module *mod);
63 extern void alternatives_smp_switch(int smp);
64 extern int alternatives_text_reserved(void *start, void *end);
65 extern bool skip_smp_alternatives;
66 #else
alternatives_smp_module_add(struct module * mod,char * name,void * locks,void * locks_end,void * text,void * text_end)67 static inline void alternatives_smp_module_add(struct module *mod, char *name,
68 					       void *locks, void *locks_end,
69 					       void *text, void *text_end) {}
alternatives_smp_module_del(struct module * mod)70 static inline void alternatives_smp_module_del(struct module *mod) {}
alternatives_smp_switch(int smp)71 static inline void alternatives_smp_switch(int smp) {}
alternatives_text_reserved(void * start,void * end)72 static inline int alternatives_text_reserved(void *start, void *end)
73 {
74 	return 0;
75 }
76 #endif	/* CONFIG_SMP */
77 
78 /* alternative assembly primitive: */
79 #define ALTERNATIVE(oldinstr, newinstr, feature)			\
80 									\
81       "661:\n\t" oldinstr "\n662:\n"					\
82       ".section .altinstructions,\"a\"\n"				\
83       "	 .long 661b - .\n"			/* label           */	\
84       "	 .long 663f - .\n"			/* new instruction */	\
85       "	 .word " __stringify(feature) "\n"	/* feature bit     */	\
86       "	 .byte 662b-661b\n"			/* sourcelen       */	\
87       "	 .byte 664f-663f\n"			/* replacementlen  */	\
88       ".previous\n"							\
89       ".section .discard,\"aw\",@progbits\n"				\
90       "	 .byte 0xff + (664f-663f) - (662b-661b)\n" /* rlen <= slen */	\
91       ".previous\n"							\
92       ".section .altinstr_replacement, \"ax\"\n"			\
93       "663:\n\t" newinstr "\n664:\n"		/* replacement     */	\
94       ".previous"
95 
96 /*
97  * This must be included *after* the definition of ALTERNATIVE due to
98  * <asm/arch_hweight.h>
99  */
100 #include <asm/cpufeature.h>
101 
102 /*
103  * Alternative instructions for different CPU types or capabilities.
104  *
105  * This allows to use optimized instructions even on generic binary
106  * kernels.
107  *
108  * length of oldinstr must be longer or equal the length of newinstr
109  * It can be padded with nops as needed.
110  *
111  * For non barrier like inlines please define new variants
112  * without volatile and memory clobber.
113  */
114 #define alternative(oldinstr, newinstr, feature)			\
115 	asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
116 
117 /*
118  * Alternative inline assembly with input.
119  *
120  * Pecularities:
121  * No memory clobber here.
122  * Argument numbers start with 1.
123  * Best is to use constraints that are fixed size (like (%1) ... "r")
124  * If you use variable sized constraints like "m" or "g" in the
125  * replacement make sure to pad to the worst case length.
126  * Leaving an unused argument 0 to keep API compatibility.
127  */
128 #define alternative_input(oldinstr, newinstr, feature, input...)	\
129 	asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)		\
130 		: : "i" (0), ## input)
131 
132 /* Like alternative_input, but with a single output argument */
133 #define alternative_io(oldinstr, newinstr, feature, output, input...)	\
134 	asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)		\
135 		: output : "i" (0), ## input)
136 
137 /* Like alternative_io, but for replacing a direct call with another one. */
138 #define alternative_call(oldfunc, newfunc, feature, output, input...)	\
139 	asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
140 		: output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
141 
142 /*
143  * use this macro(s) if you need more than one output parameter
144  * in alternative_io
145  */
146 #define ASM_OUTPUT2(a...) a
147 
148 /*
149  * use this macro if you need clobbers but no inputs in
150  * alternative_{input,io,call}()
151  */
152 #define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
153 
154 struct paravirt_patch_site;
155 #ifdef CONFIG_PARAVIRT
156 void apply_paravirt(struct paravirt_patch_site *start,
157 		    struct paravirt_patch_site *end);
158 #else
apply_paravirt(struct paravirt_patch_site * start,struct paravirt_patch_site * end)159 static inline void apply_paravirt(struct paravirt_patch_site *start,
160 				  struct paravirt_patch_site *end)
161 {}
162 #define __parainstructions	NULL
163 #define __parainstructions_end	NULL
164 #endif
165 
166 extern void *text_poke_early(void *addr, const void *opcode, size_t len);
167 
168 /*
169  * Clear and restore the kernel write-protection flag on the local CPU.
170  * Allows the kernel to edit read-only pages.
171  * Side-effect: any interrupt handler running between save and restore will have
172  * the ability to write to read-only pages.
173  *
174  * Warning:
175  * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
176  * no thread can be preempted in the instructions being modified (no iret to an
177  * invalid instruction possible) or if the instructions are changed from a
178  * consistent state to another consistent state atomically.
179  * More care must be taken when modifying code in the SMP case because of
180  * Intel's errata. text_poke_smp() takes care that errata, but still
181  * doesn't support NMI/MCE handler code modifying.
182  * On the local CPU you need to be protected again NMI or MCE handlers seeing an
183  * inconsistent instruction while you patch.
184  */
185 struct text_poke_param {
186 	void *addr;
187 	const void *opcode;
188 	size_t len;
189 };
190 
191 extern void *text_poke(void *addr, const void *opcode, size_t len);
192 extern void *text_poke_smp(void *addr, const void *opcode, size_t len);
193 extern void text_poke_smp_batch(struct text_poke_param *params, int n);
194 
195 #endif /* _ASM_X86_ALTERNATIVE_H */
196