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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 <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>
This commit is contained in:
Brian Gerst 2016-01-27 09:45:25 +01:00 committed by Ingo Molnar
parent 337e4cc840
commit 2476f2fa20
2 changed files with 12 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
arch/x86/include/asm/cpufeature.h
View File

@ -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) #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(). * Static testing of CPU features. Used the same as boot_cpu_has().
* These will statically patch the target code for additional * 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) 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" "2:\n"
".skip -(((5f-4f) - (2b-1b)) > 0) * " ".skip -(((5f-4f) - (2b-1b)) > 0) * "
"((5f-4f) - (2b-1b)),0x90\n" "((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" /* repl len */
" .byte 0\n" /* pad len */ " .byte 0\n" /* pad len */
".previous\n" ".previous\n"
: : "i" (bit), "i" (X86_FEATURE_ALWAYS) ".section .altinstr_aux,\"ax\"\n"
: : t_dynamic, t_no); "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; return true;
t_no: t_no:
return false; return false;
t_dynamic:
return __static_cpu_has(bit);
} }
#define static_cpu_has(bit) \ #define static_cpu_has(bit) \

6
arch/x86/kernel/cpu/common.c
View File

@ -1475,12 +1475,6 @@ void cpu_init(void)
} }
#endif #endif
inline bool __static_cpu_has(u16 bit)
{
return boot_cpu_has(bit);
}
EXPORT_SYMBOL_GPL(__static_cpu_has);
static void bsp_resume(void) static void bsp_resume(void)
{ {
if (this_cpu->c_bsp_resume) if (this_cpu->c_bsp_resume)