linux-kernel - [PATCH] x86/CPU/AMD: Rename the spectral chicken

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Message-Id: <20230425195024.17808-1-bp@alien8.de>
Date:   Tue, 25 Apr 2023 21:50:24 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/CPU/AMD: Rename the spectral chicken

From: "Borislav Petkov (AMD)" <bp@...en8.de>

We've had enough fun with the spectral chicken bit - name it what it
really does: it suppresses non-branch predictions.

Rename defines to make it clear that it is Zen2 only.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 arch/x86/include/asm/msr-index.h |  6 ++++--
 arch/x86/kernel/cpu/amd.c        | 22 +++++++++++-----------
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index ad35355ee43e..0094e6a1b553 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -625,8 +625,10 @@
 /* Fam 17h MSRs */
 #define MSR_F17H_IRPERF			0xc00000e9
 
-#define MSR_ZEN2_SPECTRAL_CHICKEN	0xc00110e3
-#define MSR_ZEN2_SPECTRAL_CHICKEN_BIT	BIT_ULL(1)
+/* Fam 17h, Zen2 MSRs */
+#define MSR_ZEN2_DE_CFG2			0xc00110e3
+#define MSR_ZEN2_DE_CFG2_SUPPRESS_NOBR_PRED_BIT	1
+#define MSR_ZEN2_DE_CFG2_SUPPRESS_NOBR_PRED	BIT(MSR_ZEN2_DE_CFG2_SUPPRESS_NOBR_PRED_BIT)
 
 /* Fam 16h MSRs */
 #define MSR_F16H_L2I_PERF_CTL		0xc0010230
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 571abf808ea3..70a41088e900 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -860,23 +860,23 @@ static void init_amd_bd(struct cpuinfo_x86 *c)
 	clear_rdrand_cpuid_bit(c);
 }
 
-void init_spectral_chicken(struct cpuinfo_x86 *c)
+void init_amd_zn2(struct cpuinfo_x86 *c)
 {
 #ifdef CONFIG_CPU_UNRET_ENTRY
 	u64 value;
 
 	/*
-	 * On Zen2 we offer this chicken (bit) on the altar of Speculation.
+	 * Suppress speculation from the middle of a basic block, i.e.
+	 * non-branch predictions.
 	 *
-	 * This suppresses speculation from the middle of a basic block, i.e. it
-	 * suppresses non-branch predictions.
-	 *
-	 * We use STIBP as a heuristic to filter out Zen2 from the rest of F17H
+	 * STIBP is used as a heuristic to filter out Zen2 from the rest
+	 * of family 0x17.
 	 */
-	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && cpu_has(c, X86_FEATURE_AMD_STIBP)) {
-		if (!rdmsrl_safe(MSR_ZEN2_SPECTRAL_CHICKEN, &value)) {
-			value |= MSR_ZEN2_SPECTRAL_CHICKEN_BIT;
-			wrmsrl_safe(MSR_ZEN2_SPECTRAL_CHICKEN, value);
+	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) &&
+	     cpu_has(c, X86_FEATURE_AMD_STIBP)) {
+		if (!rdmsrl_safe(MSR_ZEN2_DE_CFG2, &value)) {
+			value |= MSR_ZEN2_DE_CFG2_SUPPRESS_NOBR_PRED;
+			wrmsrl_safe(MSR_ZEN2_DE_CFG2, value);
 		}
 	}
 #endif
@@ -949,7 +949,7 @@ static void init_amd(struct cpuinfo_x86 *c)
 	case 0x12: init_amd_ln(c); break;
 	case 0x15: init_amd_bd(c); break;
 	case 0x16: init_amd_jg(c); break;
-	case 0x17: init_spectral_chicken(c);
+	case 0x17: init_amd_zn2(c);
 		   fallthrough;
 	case 0x19: init_amd_zn(c); break;
 	}
-- 
2.35.1