linux-kernel - [PATCH v4 11/13] x86/retpoline: Simplify AMD variant of retpoline thunk

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Message-Id: <1515117669-24787-12-git-send-email-dwmw@amazon.co.uk>
Date:   Fri,  5 Jan 2018 02:01:07 +0000
From:   David Woodhouse <dwmw@...zon.co.uk>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Paul Turner <pjt@...gle.com>, LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: [PATCH v4 11/13] x86/retpoline: Simplify AMD variant of retpoline thunk

On AMD (which is X86_FEATURE_K8), just the lfence is sufficient.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 arch/x86/lib/retpoline.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 958d56f..d58f8f3 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -12,7 +12,7 @@
 
 ENTRY(__x86.indirect_thunk.\reg)
 	CFI_STARTPROC
-	ALTERNATIVE "call 2f", __stringify(jmp *%\reg), X86_BUG_NO_RETPOLINE
+	ALTERNATIVE_2 "call 2f", __stringify(lfence;jmp *%\reg), X86_FEATURE_K8, __stringify(jmp *%\reg), X86_BUG_NO_RETPOLINE
 1:
 	lfence
 	jmp	1b
-- 
2.7.4