From 2476f2fa20568bd5d9e09cd35bcd73e99a6f4cc6 Mon Sep 17 00:00:00 2001 From: Brian Gerst Date: Wed, 27 Jan 2016 09:45:25 +0100 Subject: x86/alternatives: Discard dynamic check after init Move the code to do the dynamic check to the altinstr_aux section so that it is discarded after alternatives have run and a static branch has been chosen. This way we're changing the dynamic branch from C code to assembly, which makes it *substantially* smaller while avoiding a completely unnecessary call to an out of line function. Signed-off-by: Brian Gerst [ Changed it to do TESTB, as hpa suggested. ] Signed-off-by: Borislav Petkov Cc: Andrew Morton Cc: Andy Lutomirski Cc: Andy Lutomirski Cc: Boris Ostrovsky Cc: Borislav Petkov Cc: Dave Young Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Kristen Carlson Accardi Cc: Laura Abbott Cc: Linus Torvalds Cc: Peter Zijlstra (Intel) Cc: Peter Zijlstra Cc: Prarit Bhargava Cc: Ross Zwisler Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1452972124-7380-1-git-send-email-brgerst@gmail.com Link: http://lkml.kernel.org/r/20160127084525.GC30712@pd.tnic Signed-off-by: Ingo Molnar --- arch/x86/include/asm/cpufeature.h | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) (limited to 'arch/x86/include/asm/cpufeature.h') diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index 9048c1bbc519..9fba7a5dd24a 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -130,8 +130,6 @@ extern const char * const x86_bug_flags[NBUGINTS*32]; */ #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_X86_FAST_FEATURE_TESTS) -extern bool __static_cpu_has(u16 bit); - /* * Static testing of CPU features. Used the same as boot_cpu_has(). * These will statically patch the target code for additional @@ -139,7 +137,7 @@ extern bool __static_cpu_has(u16 bit); */ static __always_inline __pure bool _static_cpu_has(u16 bit) { - asm_volatile_goto("1: jmp %l[t_dynamic]\n" + asm_volatile_goto("1: jmp 6f\n" "2:\n" ".skip -(((5f-4f) - (2b-1b)) > 0) * " "((5f-4f) - (2b-1b)),0x90\n" @@ -164,13 +162,20 @@ static __always_inline __pure bool _static_cpu_has(u16 bit) " .byte 0\n" /* repl len */ " .byte 0\n" /* pad len */ ".previous\n" - : : "i" (bit), "i" (X86_FEATURE_ALWAYS) - : : t_dynamic, t_no); + ".section .altinstr_aux,\"ax\"\n" + "6:\n" + " testb %[bitnum],%[cap_byte]\n" + " jnz %l[t_yes]\n" + " jmp %l[t_no]\n" + ".previous\n" + : : "i" (bit), "i" (X86_FEATURE_ALWAYS), + [bitnum] "i" (1 << (bit & 7)), + [cap_byte] "m" (((const char *)boot_cpu_data.x86_capability)[bit >> 3]) + : : t_yes, t_no); + t_yes: return true; t_no: return false; - t_dynamic: - return __static_cpu_has(bit); } #define static_cpu_has(bit) \ -- cgit v1.2.3