linux-kernel - [PATCH v2 1/2] x86/retpoline: Add X86_FEATURE_RETPOLINE_COMMON and split RETPLINE/RETPOLINE

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Date:   Tue,  9 Jan 2018 17:56:00 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     tglx@...utronix.de
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, dwmw@...zon.co.uk, pjt@...gle.com,
        luto@...nel.org, peterz@...radead.org, thomas.lendacky@....com,
        tim.c.chen@...ux.intel.com, gregkh@...ux-foundation.org,
        dave.hansen@...el.com, jikos@...nel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH v2 1/2] x86/retpoline: Add X86_FEATURE_RETPOLINE_COMMON and split RETPLINE/RETPOLINE_AMD

From: Andi Kleen <ak@...ux.intel.com>

On 64bit we want to split X86_FEATURE_RETPOLINE and X86_FEATURE_RETPOLINE_AMD,
so that only one is set. This enables new simpler ALTERNATIVE sequences.

But 32bit requires a common flag because it uses common code for both.

So add a new X86_FEATURE_RETPOLINE_COMMON that is always set
when either X86_FEATURE_RETPOLINE or X86_FEATURE_RETPOLINE_AMD are set.

And then unset X86_FEATURE_RETPOLINE for AMD.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kernel/cpu/bugs.c         | 5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index f275447862f4..54ec16ef08d8 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -211,6 +211,7 @@
 #define X86_FEATURE_AVX512_4FMAPS	( 7*32+17) /* AVX-512 Multiply Accumulation Single precision */
 
 #define X86_FEATURE_MBA			( 7*32+18) /* Memory Bandwidth Allocation */
+#define X86_FEATURE_RETPOLINE_COMMON	( 7*32+19) /* Common code for both RETPOLINE and RETPOLINE_AMD */
 
 /* Virtualization flags: Linux defined, word 8 */
 #define X86_FEATURE_TPR_SHADOW		( 8*32+ 0) /* Intel TPR Shadow */
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index b957f771a5b7..241eae66a86b 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -155,8 +155,10 @@ void __init spectre_v2_check_boottime_disable(void)
 	retpoline_generic:
 		spectre_v2_enabled = retp_compiler() ?
 			SPECTRE_V2_RETPOLINE_GENERIC : SPECTRE_V2_RETPOLINE_MINIMAL;
+		setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
 	}
-	setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
+	setup_force_cpu_cap(X86_FEATURE_RETPOLINE_COMMON);
+
 	return;
 #else
 retpoline:
@@ -167,6 +169,7 @@ void __init spectre_v2_check_boottime_disable(void)
 disable:
 	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE);
 	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
+	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE_COMMON);
 	return;
 }
 
-- 
2.14.3