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Commit a3c8acd0 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

x86: Add new static_cpu_has() function using alternatives 



For CPU-feature-specific code that touches performance-critical paths,
introduce a static patching version of [boot_]cpu_has().  This is run
at alternatives time and is therefore not appropriate for most
initialization code, but on the other hand initialization code is
generally not performance critical.

On gcc 4.5+ this uses the new "asm goto" feature.

Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1273135546-29690-2-git-send-email-avi@redhat.com>
parent dce8bf4e

arch/x86/include/asm/cpufeature.h

+57 −0
Original line number Diff line number Diff line
@@ -175,6 +175,7 @@ 


#if defined(__KERNEL__) && !defined(__ASSEMBLY__)



#include <asm/asm.h>

#include <linux/bitops.h>



extern const char * const x86_cap_flags[NCAPINTS*32];
@@ -283,6 +284,62 @@ extern const char * const x86_power_flags[32]; 


#endif /* CONFIG_X86_64 */



/*

 * Static testing of CPU features.  Used the same as boot_cpu_has().

 * These are only valid after alternatives have run, but will statically

 * patch the target code for additional performance.

 *

 */

static __always_inline __pure bool __static_cpu_has(u8 bit)

{

#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)

		asm goto("1: jmp %l[t_no]\n"

			 "2:\n"

			 ".section .altinstructions,\"a\"\n"

			 _ASM_ALIGN "\n"

			 _ASM_PTR "1b\n"

			 _ASM_PTR "0\n" 	/* no replacement */

			 " .byte %P0\n"		/* feature bit */

			 " .byte 2b - 1b\n"	/* source len */

			 " .byte 0\n"		/* replacement len */

			 " .byte 0xff + 0 - (2b-1b)\n"	/* padding */

			 ".previous\n"

			 : : "i" (bit) : : t_no);

		return true;

	t_no:

		return false;

#else

		u8 flag;

		/* Open-coded due to __stringify() in ALTERNATIVE() */

		asm volatile("1: movb $0,%0\n"

			     "2:\n"

			     ".section .altinstructions,\"a\"\n"

			     _ASM_ALIGN "\n"

			     _ASM_PTR "1b\n"

			     _ASM_PTR "3f\n"

			     " .byte %P1\n"		/* feature bit */

			     " .byte 2b - 1b\n"		/* source len */

			     " .byte 4f - 3f\n"		/* replacement len */

			     " .byte 0xff + (4f-3f) - (2b-1b)\n" /* padding */

			     ".previous\n"

			     ".section .altinstr_replacement,\"ax\"\n"

			     "3: movb $1,%0\n"

			     "4:\n"

			     ".previous\n"

			     : "=qm" (flag) : "i" (bit));

		return flag;

#endif

}



#define static_cpu_has(bit)					\

(								\

	__builtin_constant_p(boot_cpu_has(bit)) ?		\

		boot_cpu_has(bit) :				\

	(__builtin_constant_p(bit) && !((bit) & ~0xff)) ?	\

		__static_cpu_has(bit) :				\

		boot_cpu_has(bit)				\

)



#endif /* defined(__KERNEL__) && !defined(__ASSEMBLY__) */



#endif /* _ASM_X86_CPUFEATURE_H */