Commit 1fe67aee authored by Uros Bizjak's avatar Uros Bizjak Committed by Ingo Molnar
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x86/percpu: Fix operand constraint modifier in __raw_cpu_write() 



__raw_cpu_write() with !USE_X86_SEG_SUPPORT config uses read/write
operand constraint modifier "+" for its memory location. This signals
the compiler that the location is both read and written by the asm.
This is not true, because MOV insn only writes to the output.

Correct the modifier to "=" to inform the compiler that the memory
location is only written to. This also prevents the compiler from
value tracking the undefined value from the uninitialized memory.

Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20240430091833.196482-5-ubizjak@gmail.com
parent 539615de

arch/x86/include/asm/percpu.h

+1 −1
Original line number Diff line number Diff line
@@ -178,7 +178,7 @@ do { \ 
		(void)pto_tmp__;					\

	}								\

	asm qual(__pcpu_op2_##size("mov", "%[val]", __percpu_arg([var])) \

	    : [var] "+m" (__my_cpu_var(_var))				\

	    : [var] "=m" (__my_cpu_var(_var))				\

	    : [val] __pcpu_reg_imm_##size(pto_val__));			\

} while (0)