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Commit 4a90a99c authored by Borislav Petkov's avatar Borislav Petkov Committed by H. Peter Anvin
Browse files

x86: Add a static_cpu_has_safe variant 



We want to use this in early code where alternatives might not have run
yet and for that case we fall back to the dynamic boot_cpu_has.

For that, force a 5-byte jump since the compiler could be generating
differently sized jumps for each label.

Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1370772454-6106-5-git-send-email-bp@alien8.de


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 5700f743

arch/x86/include/asm/cpufeature.h

+85 −1
Original line number Diff line number Diff line
@@ -357,6 +357,7 @@ extern const char * const x86_power_flags[32]; 


#if __GNUC__ >= 4

extern void warn_pre_alternatives(void);

extern bool __static_cpu_has_safe(u16 bit);



/*

 * Static testing of CPU features.  Used the same as boot_cpu_has().
@@ -437,11 +438,94 @@ static __always_inline __pure bool __static_cpu_has(u16 bit) 
		__static_cpu_has(bit) :				\

		boot_cpu_has(bit)				\

)



static __always_inline __pure bool _static_cpu_has_safe(u16 bit)

{

#if __GNUC__ > 4 || __GNUC_MINOR__ >= 5

/*

 * We need to spell the jumps to the compiler because, depending on the offset,

 * the replacement jump can be bigger than the original jump, and this we cannot

 * have. Thus, we force the jump to the widest, 4-byte, signed relative

 * offset even though the last would often fit in less bytes.

 */

		asm goto("1: .byte 0xe9\n .long %l[t_dynamic] - 2f\n"

			 "2:\n"

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

			 " .long 1b - .\n"		/* src offset */

			 " .long 3f - .\n"		/* repl offset */

			 " .word %P1\n"			/* always replace */

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

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

			 ".previous\n"

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

			 "3: .byte 0xe9\n .long %l[t_no] - 2b\n"

			 "4:\n"

			 ".previous\n"

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

			 " .long 1b - .\n"		/* src offset */

			 " .long 0\n"			/* no replacement */

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

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

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

			 ".previous\n"

			 : : "i" (bit), "i" (X86_FEATURE_ALWAYS)

			 : : t_dynamic, t_no);

		return true;

	t_no:

		return false;

	t_dynamic:

		return __static_cpu_has_safe(bit);

#else /* GCC_VERSION >= 40500 */

		u8 flag;

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

		asm volatile("1: movb $2,%0\n"

			     "2:\n"

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

			     " .long 1b - .\n"		/* src offset */

			     " .long 3f - .\n"		/* repl offset */

			     " .word %P2\n"		/* always replace */

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

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

			     ".previous\n"

			     ".section .discard,\"aw\",@progbits\n"

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

			     ".previous\n"

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

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

			     "4:\n"

			     ".previous\n"

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

			     " .long 1b - .\n"		/* src offset */

			     " .long 5f - .\n"		/* repl offset */

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

			     " .byte 4b - 3b\n"		/* src len */

			     " .byte 6f - 5f\n"		/* repl len */

			     ".previous\n"

			     ".section .discard,\"aw\",@progbits\n"

			     " .byte 0xff + (6f-5f) - (4b-3b)\n" /* size check */

			     ".previous\n"

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

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

			     "6:\n"

			     ".previous\n"

			     : "=qm" (flag)

			     : "i" (bit), "i" (X86_FEATURE_ALWAYS));

		return (flag == 2 ? __static_cpu_has_safe(bit) : flag);

#endif

}



#define static_cpu_has_safe(bit)				\

(								\

	__builtin_constant_p(boot_cpu_has(bit)) ?		\

		boot_cpu_has(bit) :				\

		_static_cpu_has_safe(bit)			\

)

#else

/*

 * gcc 3.x is too stupid to do the static test; fall back to dynamic.

 */

#define static_cpu_has(bit)		boot_cpu_has(bit)

#define static_cpu_has_safe(bit)	boot_cpu_has(bit)

#endif



#define cpu_has_bug(c, bit)	cpu_has(c, (bit))

arch/x86/kernel/cpu/common.c

+6 −0
Original line number Diff line number Diff line
@@ -1372,3 +1372,9 @@ void warn_pre_alternatives(void) 
}

EXPORT_SYMBOL_GPL(warn_pre_alternatives);

#endif



inline bool __static_cpu_has_safe(u16 bit)

{

	return boot_cpu_has(bit);

}

EXPORT_SYMBOL_GPL(__static_cpu_has_safe);