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authorAndi Kleen <ak@linux.intel.com>2018-01-17 14:53:28 -0800
committerThomas Gleixner <tglx@linutronix.de>2018-01-19 16:31:30 +0100
commit3f7d875566d8e79c5e0b2c9a413e91b2c29e0854 (patch)
tree0d0039aae333d220686378a027e38273c133e856
parent98f0fceec7f84d80bc053e49e596088573086421 (diff)
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
-rw-r--r--arch/x86/include/asm/nospec-branch.h7
1 files changed, 4 insertions, 3 deletions
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 19ba5ad19c65..4ad41087ce0e 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -206,16 +206,17 @@ extern char __indirect_thunk_end[];
static inline void vmexit_fill_RSB(void)
{
#ifdef CONFIG_RETPOLINE
- unsigned long loops = RSB_CLEAR_LOOPS / 2;
+ unsigned long loops;
asm volatile (ANNOTATE_NOSPEC_ALTERNATIVE
ALTERNATIVE("jmp 910f",
__stringify(__FILL_RETURN_BUFFER(%0, RSB_CLEAR_LOOPS, %1)),
X86_FEATURE_RETPOLINE)
"910:"
- : "=&r" (loops), ASM_CALL_CONSTRAINT
- : "r" (loops) : "memory" );
+ : "=r" (loops), ASM_CALL_CONSTRAINT
+ : : "memory" );
#endif
}
+
#endif /* __ASSEMBLY__ */
#endif /* __NOSPEC_BRANCH_H__ */