From: Brian Gerst brgerst@gmail.com
commit 2476f2fa20568bd5d9e09cd35bcd73e99a6f4cc6 upstream
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 brgerst@gmail.com [ Changed it to do TESTB, as hpa suggested. ] Signed-off-by: Borislav Petkov bp@suse.de Cc: Andrew Morton akpm@linux-foundation.org Cc: Andy Lutomirski luto@amacapital.net Cc: Andy Lutomirski luto@kernel.org Cc: Boris Ostrovsky boris.ostrovsky@oracle.com Cc: Borislav Petkov bp@alien8.de Cc: Dave Young dyoung@redhat.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Kristen Carlson Accardi kristen@linux.intel.com Cc: Laura Abbott labbott@fedoraproject.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra (Intel) peterz@infradead.org Cc: Peter Zijlstra peterz@infradead.org Cc: Prarit Bhargava prarit@redhat.com Cc: Ross Zwisler ross.zwisler@linux.intel.com Cc: Thomas Gleixner tglx@linutronix.de 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 mingo@kernel.org Signed-off-by: Srivatsa S. Bhat srivatsa@csail.mit.edu Reviewed-by: Matt Helsley (VMware) matt.helsley@gmail.com Reviewed-by: Alexey Makhalov amakhalov@vmware.com Reviewed-by: Bo Gan ganb@vmware.com ---
arch/x86/include/asm/cpufeature.h | 19 ++++++++++++------- arch/x86/kernel/cpu/common.c | 6 ------ 2 files changed, 12 insertions(+), 13 deletions(-)
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index 53de461..1c9d6c5 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -132,8 +132,6 @@ 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 @@ -141,7 +139,7 @@ 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" @@ -166,13 +164,20 @@ 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) \ diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index f31b26b..58d56c4 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1576,12 +1576,6 @@ void cpu_init(void) } #endif
-inline bool __static_cpu_has(u16 bit) -{ - return boot_cpu_has(bit); -} -EXPORT_SYMBOL_GPL(__static_cpu_has); - static void bsp_resume(void) { if (this_cpu->c_bsp_resume)