diff options
| author | Andi Kleen <ak@linux.intel.com> | 2018-01-18 01:53:28 +0300 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2018-01-19 18:31:30 +0300 |
| commit | 3f7d875566d8e79c5e0b2c9a413e91b2c29e0854 (patch) | |
| tree | 0d0039aae333d220686378a027e38273c133e856 | |
| parent | 98f0fceec7f84d80bc053e49e596088573086421 (diff) | |
| download | linux-3f7d875566d8e79c5e0b2c9a413e91b2c29e0854.tar.xz | |
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.h | 7 |
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__ */ |