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Commit 2476f2fa authored by Brian Gerst's avatar Brian Gerst Committed by Ingo Molnar
Browse files

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: default avatarBrian Gerst <brgerst@gmail.com>
[ Changed it to do TESTB, as hpa suggested. ]
Signed-off-by: default avatarBorislav 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: default avatarIngo Molnar <mingo@kernel.org>
parent 337e4cc8

arch/x86/include/asm/cpufeature.h

+12 −7
Original line number Diff line number Diff line
@@ -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)					\

arch/x86/kernel/cpu/common.c

+0 −6
Original line number Diff line number Diff line
@@ -1475,12 +1475,6 @@ 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)