[PATCH v5 04/12] x86/alternative: support not-feature

[Juergen Gross <jgross@xxxxxxxx>]

Add support for alternative patching for the case a feature is not
present on the current cpu.

For this purpose add a flag byte to struct alt_instr adding the
information that the inverted feature should be used.

For users of ALTERNATIVE() and friends an inverted feature is specified
by negating it, e.g.:

ALTERNATIVE(old, new, ~feature)

This requires adapting the objtool information for struct alt_instr.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V5:
- split off from next patch
- reworked to use flag byte (Boris Petkov)
---
 arch/x86/include/asm/alternative-asm.h        | 6 ++++++
 arch/x86/include/asm/alternative.h            | 8 ++++++++
 arch/x86/include/asm/cpufeature.h             | 2 ++
 arch/x86/kernel/alternative.c                 | 5 +++--
 tools/objtool/arch/x86/include/arch/special.h | 6 +++---
 5 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/alternative-asm.h 
b/arch/x86/include/asm/alternative-asm.h
index 464034db299f..9a1763550217 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -39,7 +39,13 @@
 .macro altinstruction_entry orig alt feature orig_len alt_len pad_len
        .long \orig - .
        .long \alt - .
+       .iflt \feature
+       .word ~(\feature)
+       .byte 1
+       .else
        .word \feature
+       .byte 0
+       .endif
        .byte \orig_len
        .byte \alt_len
        .byte \pad_len
diff --git a/arch/x86/include/asm/alternative.h 
b/arch/x86/include/asm/alternative.h
index 5753fb2ac489..b9749cf21ada 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -59,6 +59,8 @@ struct alt_instr {
        s32 instr_offset;       /* original instruction */
        s32 repl_offset;        /* offset to replacement instruction */
        u16 cpuid;              /* cpuid bit set for replacement */
+       u8  flag;               /* flag byte */
+#define ALTINSTR_FLAG_INV      0x01
        u8  instrlen;           /* length of original instruction */
        u8  replacementlen;     /* length of new instruction */
        u8  padlen;             /* length of build-time padding */
@@ -145,7 +147,13 @@ static inline int alternatives_text_reserved(void *start, 
void *end)
 #define ALTINSTR_ENTRY(feature, num)                                         \
        " .long 661b - .\n"                             /* label           */ \
        " .long " b_replacement(num)"f - .\n"           /* new instruction */ \
+       " .iflt " __stringify(feature) "\n"             /* inverted?       */ \
+       " .word ~(" __stringify(feature) ")\n"          /* feature bit     */ \
+       " .byte " __stringify(ALTINSTR_FLAG_INV) "\n"   /* flag byte       */ \
+       " .else\n"                                                            \
        " .word " __stringify(feature) "\n"             /* feature bit     */ \
+       " .byte 0\n"                                    /* flag byte       */ \
+       " .endif\n"                                                           \
        " .byte " alt_total_slen "\n"                   /* source len      */ \
        " .byte " alt_rlen(num) "\n"                    /* replacement len */ \
        " .byte " alt_pad_len "\n"                      /* pad len */
diff --git a/arch/x86/include/asm/cpufeature.h 
b/arch/x86/include/asm/cpufeature.h
index 1728d4ce5730..f060d3186ee4 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -184,6 +184,7 @@ static __always_inline bool _static_cpu_has(u16 bit)
                 " .long 1b - .\n"              /* src offset */
                 " .long 4f - .\n"              /* repl offset */
                 " .word %P[always]\n"          /* always replace */
+                " .byte 0\n"                   /* flag byte */
                 " .byte 3b - 1b\n"             /* src len */
                 " .byte 5f - 4f\n"             /* repl len */
                 " .byte 3b - 2b\n"             /* pad len */
@@ -196,6 +197,7 @@ static __always_inline bool _static_cpu_has(u16 bit)
                 " .long 1b - .\n"              /* src offset */
                 " .long 0\n"                   /* no replacement */
                 " .word %P[feature]\n"         /* feature bit */
+                " .byte 0\n"                   /* flag byte */
                 " .byte 3b - 1b\n"             /* src len */
                 " .byte 0\n"                   /* repl len */
                 " .byte 0\n"                   /* pad len */
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 8d778e46725d..1296a90aa5b8 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -393,14 +393,15 @@ void __init_or_module noinline apply_alternatives(struct 
alt_instr *start,
                replacement = (u8 *)&a->repl_offset + a->repl_offset;
                BUG_ON(a->instrlen > sizeof(insn_buff));
                BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32);
-               if (!boot_cpu_has(a->cpuid)) {
+               if (!boot_cpu_has(a->cpuid) == !(a->flag & ALTINSTR_FLAG_INV)) {
                        if (a->padlen > 1)
                                optimize_nops(a, instr);
 
                        continue;
                }
 
-               DPRINTK("feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, 
len: %d), pad: %d",
+               DPRINTK("feat: %s%d*32+%d, old: (%pS (%px) len: %d), repl: 
(%px, len: %d), pad: %d",
+                       (a->flag & ALTINSTR_FLAG_INV) ? "~" : "",
                        a->cpuid >> 5,
                        a->cpuid & 0x1f,
                        instr, instr, a->instrlen,
diff --git a/tools/objtool/arch/x86/include/arch/special.h 
b/tools/objtool/arch/x86/include/arch/special.h
index d818b2bffa02..afde39063963 100644
--- a/tools/objtool/arch/x86/include/arch/special.h
+++ b/tools/objtool/arch/x86/include/arch/special.h
@@ -10,11 +10,11 @@
 #define JUMP_ORIG_OFFSET       0
 #define JUMP_NEW_OFFSET                4
 
-#define ALT_ENTRY_SIZE         13
+#define ALT_ENTRY_SIZE         14
 #define ALT_ORIG_OFFSET                0
 #define ALT_NEW_OFFSET         4
 #define ALT_FEATURE_OFFSET     8
-#define ALT_ORIG_LEN_OFFSET    10
-#define ALT_NEW_LEN_OFFSET     11
+#define ALT_ORIG_LEN_OFFSET    11
+#define ALT_NEW_LEN_OFFSET     12
 
 #endif /* _X86_ARCH_SPECIAL_H */
-- 
2.26.2