linux-kernel - [PATCH v3 1/3] x86/retpoline: Add X86_FEATURE_RETPOLINE

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Date:   Tue,  9 Jan 2018 18:28:29 -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 v3 1/3] x86/retpoline: Add X86_FEATURE_RETPOLINE_GENERIC

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.

Rename the existing X86_FEATURE_RETPOLINE to X86_FEATURE_GENERIC
Use the existing X86_FEATURE_RETPOLINE as a common flag
that is set for both the AMD and generic Retpoline.

Then don't set the generic RETPOLINE flag for AMD.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/include/asm/cpufeatures.h | 3 ++-
 arch/x86/kernel/cpu/bugs.c         | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index f275447862f4..9db5ed0e01a9 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -203,7 +203,7 @@
 #define X86_FEATURE_PROC_FEEDBACK	( 7*32+ 9) /* AMD ProcFeedbackInterface */
 #define X86_FEATURE_SME			( 7*32+10) /* AMD Secure Memory Encryption */
 #define X86_FEATURE_PTI			( 7*32+11) /* Kernel Page Table Isolation enabled */
-#define X86_FEATURE_RETPOLINE		( 7*32+12) /* Generic Retpoline mitigation for Spectre variant 2 */
+#define X86_FEATURE_RETPOLINE_GENERIC	( 7*32+12) /* Generic Retpoline mitigation for Spectre variant 2 */
 #define X86_FEATURE_RETPOLINE_AMD	( 7*32+13) /* AMD Retpoline mitigation for Spectre variant 2 */
 #define X86_FEATURE_INTEL_PPIN		( 7*32+14) /* Intel Processor Inventory Number */
 #define X86_FEATURE_INTEL_PT		( 7*32+15) /* Intel Processor Trace */
@@ -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		( 7*32+19) /* Common code for both RETPOLINE_GENERIC 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..68b08967a6e1 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -155,6 +155,7 @@ 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_GENERIC);
 	}
 	setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
 	return;
@@ -165,8 +166,9 @@ void __init spectre_v2_check_boottime_disable(void)
 	pr_err("kernel not compiled with retpoline; no mitigation available!");
 #endif
 disable:
-	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE);
+	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE_GENERIC);
 	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
+	setup_clear_cpu_cap(X86_FEATURE_RETPOLINE);
 	return;
 }
 
-- 
2.14.3