linux-kernel - Re: [PATCH] x86/cpufeatures: Cleanup AMD speculation feature bits

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Date:   Fri, 26 Jan 2018 22:52:09 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     David Woodhouse <dwmw2@...radead.org>, x86-ml <x86@...nel.org>,
        linux-tip-commits@...r.kernel.org, hpa@...or.com,
        gregkh@...uxfoundation.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, mingo@...nel.org
Subject: Re: [PATCH] x86/cpufeatures: Cleanup AMD speculation feature bits

On Fri, Jan 26, 2018 at 03:06:20PM -0600, Tom Lendacky wrote:
> So I like the idea of AMD_IBRS/AMD_IBPB/AMD_STIBP and then use the magic
> quotes as appropriate.  We could probably use the magic quotes on
> AMD_STIBP and set X86_FEATURE_STIBP when we see X86_FEATURE_AMD_STIBP.

Like this?

We set the respective Intel features when we detect the AMD ones so that
we get correct /proc/cpuinfo strings. The respective AMD ones are not
shown.

---
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 40f92eff09df..73080d5a5696 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -272,9 +272,9 @@
 #define X86_FEATURE_CLZERO		(13*32+ 0) /* CLZERO instruction */
 #define X86_FEATURE_IRPERF		(13*32+ 1) /* Instructions Retired Count */
 #define X86_FEATURE_XSAVEERPTR		(13*32+ 2) /* Always save/restore FP error pointers */
-#define X86_FEATURE_AMD_PRED_CMD	(13*32+12) /* Prediction Command MSR (AMD) */
-#define X86_FEATURE_AMD_SPEC_CTRL	(13*32+14) /* Speculation Control MSR only (AMD) */
-#define X86_FEATURE_AMD_STIBP		(13*32+15) /* Single Thread Indirect Branch Predictors (AMD) */
+#define X86_FEATURE_AMD_IBPB		(13*32+12) /* "" Indirect Branch Prediction Barrier MSR */
+#define X86_FEATURE_AMD_IBRS		(13*32+14) /* "" Speculation Control MSR only */
+#define X86_FEATURE_AMD_STIBP		(13*32+15) /* "" Single Thread Indirect Branch Predictors */
 
 /* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
 #define X86_FEATURE_DTHERM		(14*32+ 0) /* Digital Thermal Sensor */
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index ea831c858195..14c8a7869450 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -872,6 +872,12 @@ static void init_amd(struct cpuinfo_x86 *c)
 	/* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
 	if (!cpu_has(c, X86_FEATURE_XENPV))
 		set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+
+	if (cpu_has(c, X86_FEATURE_AMD_IBRS))
+		set_cpu_cap(c, X86_FEATURE_IBRS);
+
+	if (cpu_has(c, X86_FEATURE_AMD_STIBP))
+		set_cpu_cap(c, X86_FEATURE_STIBP);
 }
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index c988a8acb0d5..be068aea6bda 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -266,7 +266,7 @@ static void __init spectre_v2_select_mitigation(void)
 
 	/* Initialize Indirect Branch Prediction Barrier if supported */
 	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL) ||
-	    boot_cpu_has(X86_FEATURE_AMD_PRED_CMD)) {
+	    boot_cpu_has(X86_FEATURE_AMD_IBPB)) {
 		setup_force_cpu_cap(X86_FEATURE_IBPB);
 		pr_info("Enabling Indirect Branch Prediction Barrier\n");
 	}
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 7a3d216875fc..571249b8bc00 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -177,14 +177,14 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 
 	if ((cpu_has(c, X86_FEATURE_SPEC_CTRL) ||
 	     cpu_has(c, X86_FEATURE_STIBP) ||
-	     cpu_has(c, X86_FEATURE_AMD_SPEC_CTRL) ||
-	     cpu_has(c, X86_FEATURE_AMD_PRED_CMD) ||
+	     cpu_has(c, X86_FEATURE_AMD_IBRS) ||
+	     cpu_has(c, X86_FEATURE_AMD_IBPB) ||
 	     cpu_has(c, X86_FEATURE_AMD_STIBP)) && bad_spectre_microcode(c)) {
 		pr_warn("Intel Spectre v2 broken microcode detected; disabling SPEC_CTRL\n");
 		clear_cpu_cap(c, X86_FEATURE_SPEC_CTRL);
 		clear_cpu_cap(c, X86_FEATURE_STIBP);
-		clear_cpu_cap(c, X86_FEATURE_AMD_SPEC_CTRL);
-		clear_cpu_cap(c, X86_FEATURE_AMD_PRED_CMD);
+		clear_cpu_cap(c, X86_FEATURE_AMD_IBRS);
+		clear_cpu_cap(c, X86_FEATURE_AMD_IBPB);
 		clear_cpu_cap(c, X86_FEATURE_AMD_STIBP);
 	}
 

-- 
Regards/Gruss,
    Boris.

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