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authorAndi Kleen <ak@linux.intel.com>2018-01-17 14:53:28 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-01-23 19:50:18 +0100
commit11e619414b69b7f1e47baac72c5be589d86e5393 (patch)
treed077e794319a4eea9a2b6286bda9d27023198cc0
parent58f96ac5dba6b66d9fb4e0072e0e01df0360a43f (diff)
x86/retpoline: Optimize inline assembler for vmexit_fill_RSB
commit 3f7d875566d8e79c5e0b2c9a413e91b2c29e0854 upstream. 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 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 4f7a5d3fed91..492370b9b35b 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -183,15 +183,16 @@ 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 (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__ */