alternative.h

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#ifndef _ASM_X86_ALTERNATIVE_H
#define _ASM_X86_ALTERNATIVE_H

#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/stringify.h>
#include <asm/asm.h>

/*
 * Alternative inline assembly for SMP.
 *
 * The LOCK_PREFIX macro defined here replaces the LOCK and
 * LOCK_PREFIX macros used everywhere in the source tree.
 *
 * SMP alternatives use the same data structures as the other
 * alternatives and the X86_FEATURE_UP flag to indicate the case of a
 * UP system running a SMP kernel.  The existing apply_alternatives()
 * works fine for patching a SMP kernel for UP.
 *
 * The SMP alternative tables can be kept after boot and contain both
 * UP and SMP versions of the instructions to allow switching back to
 * SMP at runtime, when hotplugging in a new CPU, which is especially
 * useful in virtualized environments.
 *
 * The very common lock prefix is handled as special case in a
 * separate table which is a pure address list without replacement ptr
 * and size information.  That keeps the table sizes small.
 */

#ifdef CONFIG_SMP
#define LOCK_PREFIX_HERE \
        ".pushsection .smp_locks,\"a\"\n"   \
        ".balign 4\n"               \
        ".long 671f - .\n" /* offset */     \
        ".popsection\n"             \
        "671:"

#define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "

#else /* ! CONFIG_SMP */
#define LOCK_PREFIX_HERE ""
#define LOCK_PREFIX ""
#endif

struct alt_instr {
    s32 instr_offset;   /* original instruction */
    s32 repl_offset;    /* offset to replacement instruction */
    u16 cpuid;      /* cpuid bit set for replacement */
    u8  instrlen;       /* length of original instruction */
    u8  replacementlen; /* length of new instruction, <= instrlen */
};

extern void alternative_instructions(void);
extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);

struct module;

#ifdef CONFIG_SMP
extern void alternatives_smp_module_add(struct module *mod, char *name,
                    void *locks, void *locks_end,
                    void *text, void *text_end);
extern void alternatives_smp_module_del(struct module *mod);
extern void alternatives_enable_smp(void);
extern int alternatives_text_reserved(void *start, void *end);
extern bool skip_smp_alternatives;
#else
static inline void alternatives_smp_module_add(struct module *mod, char *name,
                           void *locks, void *locks_end,
                           void *text, void *text_end) {}
static inline void alternatives_smp_module_del(struct module *mod) {}
static inline void alternatives_enable_smp(void) {}
static inline int alternatives_text_reserved(void *start, void *end)
{
    return 0;
}
#endif  /* CONFIG_SMP */

#define OLDINSTR(oldinstr)  "661:\n\t" oldinstr "\n662:\n"

#define b_replacement(number)   "663"#number
#define e_replacement(number)   "664"#number

#define alt_slen "662b-661b"
#define alt_rlen(number) e_replacement(number)"f-"b_replacement(number)"f"

#define ALTINSTR_ENTRY(feature, number)                       \
    " .long 661b - .\n"             /* label           */ \
    " .long " b_replacement(number)"f - .\n"    /* new instruction */ \
    " .word " __stringify(feature) "\n"     /* feature bit     */ \
    " .byte " alt_slen "\n"             /* source len      */ \
    " .byte " alt_rlen(number) "\n"         /* replacement len */

#define DISCARD_ENTRY(number)               /* rlen <= slen */    \
    " .byte 0xff + (" alt_rlen(number) ") - (" alt_slen ")\n"

#define ALTINSTR_REPLACEMENT(newinstr, feature, number) /* replacement */     \
    b_replacement(number)":\n\t" newinstr "\n" e_replacement(number) ":\n\t"

/* alternative assembly primitive: */
#define ALTERNATIVE(oldinstr, newinstr, feature)            \
    OLDINSTR(oldinstr)                      \
    ".pushsection .altinstructions,\"a\"\n"             \
    ALTINSTR_ENTRY(feature, 1)                  \
    ".popsection\n"                         \
    ".pushsection .discard,\"aw\",@progbits\n"          \
    DISCARD_ENTRY(1)                        \
    ".popsection\n"                         \
    ".pushsection .altinstr_replacement, \"ax\"\n"          \
    ALTINSTR_REPLACEMENT(newinstr, feature, 1)          \
    ".popsection"

#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
    OLDINSTR(oldinstr)                      \
    ".pushsection .altinstructions,\"a\"\n"             \
    ALTINSTR_ENTRY(feature1, 1)                 \
    ALTINSTR_ENTRY(feature2, 2)                 \
    ".popsection\n"                         \
    ".pushsection .discard,\"aw\",@progbits\n"          \
    DISCARD_ENTRY(1)                        \
    DISCARD_ENTRY(2)                        \
    ".popsection\n"                         \
    ".pushsection .altinstr_replacement, \"ax\"\n"          \
    ALTINSTR_REPLACEMENT(newinstr1, feature1, 1)            \
    ALTINSTR_REPLACEMENT(newinstr2, feature2, 2)            \
    ".popsection"

/*
 * This must be included *after* the definition of ALTERNATIVE due to
 * <asm/arch_hweight.h>
 */
#include <asm/cpufeature.h>

/*
 * Alternative instructions for different CPU types or capabilities.
 *
 * This allows to use optimized instructions even on generic binary
 * kernels.
 *
 * length of oldinstr must be longer or equal the length of newinstr
 * It can be padded with nops as needed.
 *
 * For non barrier like inlines please define new variants
 * without volatile and memory clobber.
 */
#define alternative(oldinstr, newinstr, feature)            \
    asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")

/*
 * Alternative inline assembly with input.
 *
 * Pecularities:
 * No memory clobber here.
 * Argument numbers start with 1.
 * Best is to use constraints that are fixed size (like (%1) ... "r")
 * If you use variable sized constraints like "m" or "g" in the
 * replacement make sure to pad to the worst case length.
 * Leaving an unused argument 0 to keep API compatibility.
 */
#define alternative_input(oldinstr, newinstr, feature, input...)    \
    asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)      \
        : : "i" (0), ## input)

/* Like alternative_input, but with a single output argument */
#define alternative_io(oldinstr, newinstr, feature, output, input...)   \
    asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)      \
        : output : "i" (0), ## input)

/* Like alternative_io, but for replacing a direct call with another one. */
#define alternative_call(oldfunc, newfunc, feature, output, input...)   \
    asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
        : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)

/*
 * Like alternative_call, but there are two features and respective functions.
 * If CPU has feature2, function2 is used.
 * Otherwise, if CPU has feature1, function1 is used.
 * Otherwise, old function is used.
 */
#define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
               output, input...)                      \
    asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
        "call %P[new2]", feature2)                    \
        : output : [old] "i" (oldfunc), [new1] "i" (newfunc1),        \
        [new2] "i" (newfunc2), ## input)

/*
 * use this macro(s) if you need more than one output parameter
 * in alternative_io
 */
#define ASM_OUTPUT2(a...) a

/*
 * use this macro if you need clobbers but no inputs in
 * alternative_{input,io,call}()
 */
#define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr

struct paravirt_patch_site;
#ifdef CONFIG_PARAVIRT
void apply_paravirt(struct paravirt_patch_site *start,
            struct paravirt_patch_site *end);
#else
static inline void apply_paravirt(struct paravirt_patch_site *start,
                  struct paravirt_patch_site *end)
{}
#define __parainstructions  NULL
#define __parainstructions_end  NULL
#endif

extern void *text_poke_early(void *addr, const void *opcode, size_t len);

/*
 * Clear and restore the kernel write-protection flag on the local CPU.
 * Allows the kernel to edit read-only pages.
 * Side-effect: any interrupt handler running between save and restore will have
 * the ability to write to read-only pages.
 *
 * Warning:
 * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
 * no thread can be preempted in the instructions being modified (no iret to an
 * invalid instruction possible) or if the instructions are changed from a
 * consistent state to another consistent state atomically.
 * More care must be taken when modifying code in the SMP case because of
 * Intel's errata. text_poke_smp() takes care that errata, but still
 * doesn't support NMI/MCE handler code modifying.
 * On the local CPU you need to be protected again NMI or MCE handlers seeing an
 * inconsistent instruction while you patch.
 */
struct text_poke_param {
    void *addr;
    const void *opcode;
    size_t len;
};

extern void *text_poke(void *addr, const void *opcode, size_t len);
extern void *text_poke_smp(void *addr, const void *opcode, size_t len);
extern void text_poke_smp_batch(struct text_poke_param *params, int n);

#endif /* _ASM_X86_ALTERNATIVE_H */