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x86/retpoline: Optimize inline assembler for vmexit_fill_RSB
The generated assembler for the C fill RSB inline asm operations has several issues: - The C code sets up the loop register, which is then immediately overwritten in __FILL_RETURN_BUFFER with the same value again. - The C code also passes in the iteration count in another register, which is not used at all. Remove these two unnecessary operations. Just rely on the single constant passed to the macro for the iterations. Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: David Woodhouse <dwmw@amazon.co.uk> Cc: dave.hansen@intel.com Cc: gregkh@linuxfoundation.org Cc: torvalds@linux-foundation.org Cc: arjan@linux.intel.com Link: https://lkml.kernel.org/r/20180117225328.15414-1-andi@firstfloor.org
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1 changed files with 4 additions and 3 deletions
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@ -206,16 +206,17 @@ extern char __indirect_thunk_end[];
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static inline void vmexit_fill_RSB(void)
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{
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#ifdef CONFIG_RETPOLINE
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unsigned long loops = RSB_CLEAR_LOOPS / 2;
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unsigned long loops;
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asm volatile (ANNOTATE_NOSPEC_ALTERNATIVE
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ALTERNATIVE("jmp 910f",
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__stringify(__FILL_RETURN_BUFFER(%0, RSB_CLEAR_LOOPS, %1)),
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X86_FEATURE_RETPOLINE)
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"910:"
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: "=&r" (loops), ASM_CALL_CONSTRAINT
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: "r" (loops) : "memory" );
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: "=r" (loops), ASM_CALL_CONSTRAINT
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: : "memory" );
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#endif
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}
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#endif /* __ASSEMBLY__ */
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#endif /* __NOSPEC_BRANCH_H__ */
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