Merge tag 'alternatives_padding' of git://git.kernel.org/pub/scm/linux/kernel/git/bp/bp into x86/asm

Pull alternative instructions framework improvements from Borislav Petkov:

 "A more involved rework of the alternatives framework to be able to
  pad instructions and thus make using the alternatives macros more
  straightforward and without having to figure out old and new instruction
  sizes but have the toolchain figure that out for us.

  Furthermore, it optimizes JMPs used so that fetch and decode can be
  relieved with smaller versions of the JMPs, where possible.

  Some stats:

    x86_64 defconfig:

    Alternatives sites total:               2478
    Total padding added (in Bytes):         6051

  The padding is currently done for:

    X86_FEATURE_ALWAYS
    X86_FEATURE_ERMS
    X86_FEATURE_LFENCE_RDTSC
    X86_FEATURE_MFENCE_RDTSC
    X86_FEATURE_SMAP

  This is with the latest version of the patchset. Of course, on each
  machine the alternatives sites actually being patched are a proper
  subset of the total number."

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 17 insertions, 13 deletions

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index d6428ea5d316..0f7a5a1a8db2 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -419,6 +419,7 @@ static __always_inline __pure bool __static_cpu_has(u16 bit)
 			 " .word %P0\n"		/* 1: do replace */
 			 " .byte 2b - 1b\n"	/* source len */
 			 " .byte 0\n"		/* replacement len */
+			 " .byte 0\n"		/* pad len */
 			 ".previous\n"
 			 /* skipping size check since replacement size = 0 */
 			 : : "i" (X86_FEATURE_ALWAYS) : : t_warn);
@@ -433,6 +434,7 @@ static __always_inline __pure bool __static_cpu_has(u16 bit)
 			 " .word %P0\n"		/* feature bit */
 			 " .byte 2b - 1b\n"	/* source len */
 			 " .byte 0\n"		/* replacement len */
+			 " .byte 0\n"		/* pad len */
 			 ".previous\n"
 			 /* skipping size check since replacement size = 0 */
 			 : : "i" (bit) : : t_no);
@@ -458,6 +460,7 @@ static __always_inline __pure bool __static_cpu_has(u16 bit)
 			     " .word %P1\n"		/* feature bit */
 			     " .byte 2b - 1b\n"		/* source len */
 			     " .byte 4f - 3f\n"		/* replacement len */
+			     " .byte 0\n"		/* pad len */
 			     ".previous\n"
 			     ".section .discard,\"aw\",@progbits\n"
 			     " .byte 0xff + (4f-3f) - (2b-1b)\n" /* size check */
@@ -484,31 +487,30 @@ static __always_inline __pure bool __static_cpu_has(u16 bit)
 static __always_inline __pure bool _static_cpu_has_safe(u16 bit)
 {
 #ifdef CC_HAVE_ASM_GOTO
-/*
- * We need to spell the jumps to the compiler because, depending on the offset,
- * the replacement jump can be bigger than the original jump, and this we cannot
- * have. Thus, we force the jump to the widest, 4-byte, signed relative
- * offset even though the last would often fit in less bytes.
- */
-		asm_volatile_goto("1: .byte 0xe9\n .long %l[t_dynamic] - 2f\n"
+		asm_volatile_goto("1: jmp %l[t_dynamic]\n"
 			 "2:\n"
+			 ".skip -(((5f-4f) - (2b-1b)) > 0) * "
+			         "((5f-4f) - (2b-1b)),0x90\n"
+			 "3:\n"
 			 ".section .altinstructions,\"a\"\n"
 			 " .long 1b - .\n"		/* src offset */
-			 " .long 3f - .\n"		/* repl offset */
+			 " .long 4f - .\n"		/* repl offset */
 			 " .word %P1\n"			/* always replace */
-			 " .byte 2b - 1b\n"		/* src len */
-			 " .byte 4f - 3f\n"		/* repl len */
+			 " .byte 3b - 1b\n"		/* src len */
+			 " .byte 5f - 4f\n"		/* repl len */
+			 " .byte 3b - 2b\n"		/* pad len */
 			 ".previous\n"
 			 ".section .altinstr_replacement,\"ax\"\n"
-			 "3: .byte 0xe9\n .long %l[t_no] - 2b\n"
-			 "4:\n"
+			 "4: jmp %l[t_no]\n"
+			 "5:\n"
 			 ".previous\n"
 			 ".section .altinstructions,\"a\"\n"
 			 " .long 1b - .\n"		/* src offset */
 			 " .long 0\n"			/* no replacement */
 			 " .word %P0\n"			/* feature bit */
-			 " .byte 2b - 1b\n"		/* src len */
+			 " .byte 3b - 1b\n"		/* src len */
 			 " .byte 0\n"			/* repl len */
+			 " .byte 0\n"			/* pad len */
 			 ".previous\n"
 			 : : "i" (bit), "i" (X86_FEATURE_ALWAYS)
 			 : : t_dynamic, t_no);
@@ -528,6 +530,7 @@ static __always_inline __pure bool _static_cpu_has_safe(u16 bit)
 			     " .word %P2\n"		/* always replace */
 			     " .byte 2b - 1b\n"		/* source len */
 			     " .byte 4f - 3f\n"		/* replacement len */
+			     " .byte 0\n"		/* pad len */
 			     ".previous\n"
 			     ".section .discard,\"aw\",@progbits\n"
 			     " .byte 0xff + (4f-3f) - (2b-1b)\n" /* size check */
@@ -542,6 +545,7 @@ static __always_inline __pure bool _static_cpu_has_safe(u16 bit)
 			     " .word %P1\n"		/* feature bit */
 			     " .byte 4b - 3b\n"		/* src len */
 			     " .byte 6f - 5f\n"		/* repl len */
+			     " .byte 0\n"		/* pad len */
 			     ".previous\n"
 			     ".section .discard,\"aw\",@progbits\n"
 			     " .byte 0xff + (6f-5f) - (4b-3b)\n" /* size check */