x86, alternatives: Use 16-bit numbers for cpufeature index

We already have cpufeature indicies above 255, so use a 16-bit number
for the alternatives index.  This consumes a padding field and so
doesn't add any size, but it means that abusing the padding field to
create assembly errors on overflow no longer works.  We can retain the
test simply by redirecting it to the .discard section, however.

[ v3: updated to include open-coded locations ]
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
LKML-Reference: <tip-f88731e3068f9d1392ba71cc9f50f035d26a0d4f@git.kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/include/asm/alternative.h

@@ -45,10 +45,9 @@
 struct alt_instr {
 	u8 *instr;		/* original instruction */
 	u8 *replacement;
-	u8  cpuid;		/* cpuid bit set for replacement */
+	u16 cpuid;		/* cpuid bit set for replacement */
 	u8  instrlen;		/* length of original instruction */
 	u8  replacementlen;	/* length of new instruction, <= instrlen */
-	u8  pad1;
 #ifdef CONFIG_X86_64
 	u32 pad2;
 #endif
@@ -86,9 +85,11 @@ static inline int alternatives_text_reserved(void *start, void *end)
       _ASM_ALIGN "\n"							\
       _ASM_PTR "661b\n"				/* label           */	\
       _ASM_PTR "663f\n"				/* new instruction */	\
-      "	 .byte " __stringify(feature) "\n"	/* feature bit     */	\
+      "	 .word " __stringify(feature) "\n"	/* feature bit     */	\
       "	 .byte 662b-661b\n"			/* sourcelen       */	\
       "	 .byte 664f-663f\n"			/* replacementlen  */	\
+      ".previous\n"							\
+      ".section .discard,\"aw\",@progbits\n"				\
       "	 .byte 0xff + (664f-663f) - (662b-661b)\n" /* rlen <= slen */	\
       ".previous\n"							\
       ".section .altinstr_replacement, \"ax\"\n"			\

arch/x86/include/asm/cpufeature.h

@@ -291,7 +291,7 @@ extern const char * const x86_power_flags[32];
  * patch the target code for additional performance.
  *
  */
-static __always_inline __pure bool __static_cpu_has(u8 bit)
+static __always_inline __pure bool __static_cpu_has(u16 bit)
 {
 #if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
 		asm goto("1: jmp %l[t_no]\n"
@@ -300,11 +300,11 @@ static __always_inline __pure bool __static_cpu_has(u8 bit)
 			 _ASM_ALIGN "\n"
 			 _ASM_PTR "1b\n"
 			 _ASM_PTR "0\n" 	/* no replacement */
-			 " .byte %P0\n"		/* feature bit */
+			 " .word %P0\n"		/* feature bit */
 			 " .byte 2b - 1b\n"	/* source len */
 			 " .byte 0\n"		/* replacement len */
-			 " .byte 0xff + 0 - (2b-1b)\n"	/* padding */
 			 ".previous\n"
+			 /* skipping size check since replacement size = 0 */
 			 : : "i" (bit) : : t_no);
 		return true;
 	t_no:
@@ -318,10 +318,12 @@ static __always_inline __pure bool __static_cpu_has(u8 bit)
 			     _ASM_ALIGN "\n"
 			     _ASM_PTR "1b\n"
 			     _ASM_PTR "3f\n"
-			     " .byte %P1\n"		/* feature bit */
+			     " .word %P1\n"		/* feature bit */
 			     " .byte 2b - 1b\n"		/* source len */
 			     " .byte 4f - 3f\n"		/* replacement len */
-			     " .byte 0xff + (4f-3f) - (2b-1b)\n" /* padding */
+			     ".previous\n"
+			     ".section .discard,\"aw\",@progbits\n"
+			     " .byte 0xff + (4f-3f) - (2b-1b)\n" /* size check */
 			     ".previous\n"
 			     ".section .altinstr_replacement,\"ax\"\n"
 			     "3: movb $1,%0\n"
@@ -337,7 +339,7 @@ static __always_inline __pure bool __static_cpu_has(u8 bit)
 (								\
 	__builtin_constant_p(boot_cpu_has(bit)) ?		\
 		boot_cpu_has(bit) :				\
-	(__builtin_constant_p(bit) && !((bit) & ~0xff)) ?	\
+	__builtin_constant_p(bit) ?				\
 		__static_cpu_has(bit) :				\
 		boot_cpu_has(bit)				\
 )

arch/x86/kernel/entry_32.S

@@ -914,7 +914,7 @@ ENTRY(simd_coprocessor_error)
 	.balign 4
 	.long 661b
 	.long 663f
-	.byte X86_FEATURE_XMM
+	.word X86_FEATURE_XMM
 	.byte 662b-661b
 	.byte 664f-663f
 .previous

arch/x86/lib/clear_page_64.S

@@ -52,7 +52,7 @@ ENDPROC(clear_page)
 	.align 8
 	.quad clear_page
 	.quad 1b
-	.byte X86_FEATURE_REP_GOOD
+	.word X86_FEATURE_REP_GOOD
 	.byte .Lclear_page_end - clear_page
 	.byte 2b - 1b
 	.previous

arch/x86/lib/copy_page_64.S

@@ -113,7 +113,7 @@ ENDPROC(copy_page)
 	.align 8
 	.quad copy_page
 	.quad 1b
-	.byte X86_FEATURE_REP_GOOD
+	.word X86_FEATURE_REP_GOOD
 	.byte .Lcopy_page_end - copy_page
 	.byte 2b - 1b
 	.previous

arch/x86/lib/memcpy_64.S

@@ -131,7 +131,7 @@ ENDPROC(__memcpy)
 	.align 8
 	.quad memcpy
 	.quad .Lmemcpy_c
-	.byte X86_FEATURE_REP_GOOD
+	.word X86_FEATURE_REP_GOOD
 
 	/*
 	 * Replace only beginning, memcpy is used to apply alternatives,

arch/x86/lib/memset_64.S

@@ -121,7 +121,7 @@ ENDPROC(__memset)
 	.align 8
 	.quad memset
 	.quad .Lmemset_c
-	.byte X86_FEATURE_REP_GOOD
+	.word X86_FEATURE_REP_GOOD
 	.byte .Lfinal - memset
 	.byte .Lmemset_e - .Lmemset_c
 	.previous