From: Mikulas Patocka <mpatocka@redhat.com>
Date: Tue, 11 Jul 2017 11:44:05 +0000 (-0400)
Subject: x86/cpu: Use indirect call to measure performance in init_amd_k6()
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=5f8a16156aa1b2d0223eaee9dacdfb9bc096f610;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

x86/cpu: Use indirect call to measure performance in init_amd_k6()

This old piece of code is supposed to measure the performance of indirect
calls to determine if the processor is buggy or not, however the compiler
optimizer turns it into a direct call.

Use the OPTIMIZER_HIDE_VAR() macro to thwart the optimization, so that a real
indirect call is generated.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1707110737530.8746@file01.intranet.prod.int.rdu2.redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index bb5abe8f5fd4..3b9e220621f8 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -134,6 +134,7 @@ static void init_amd_k6(struct cpuinfo_x86 *c)
 
 		n = K6_BUG_LOOP;
 		f_vide = vide;
+		OPTIMIZER_HIDE_VAR(f_vide);
 		d = rdtsc();
 		while (n--)
 			f_vide();