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From:   David Woodhouse <dwmw@amazon.co.uk>
To:     arjan@linux.intel.com, tglx@linutronix.de, karahmed@amazon.de,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        tim.c.chen@linux.intel.com, bp@alien8.de, peterz@infradead.org,
        pbonzini@redhat.com, ak@linux.intel.com,
        torvalds@linux-foundation.org, gregkh@linux-foundation.org,
        dave.hansen@intel.com, gnomes@lxorguk.ukuu.org.uk,
        ashok.raj@intel.com, mingo@kernel.org
Subject: [PATCH v4 5/7] x86/pti: Do not enable PTI on processors which are not vulnerable to Meltdown
Date:   Thu, 25 Jan 2018 09:23:07 +0000
Message-Id: <1516872189-16577-6-git-send-email-dwmw@amazon.co.uk>
In-Reply-To: <1516872189-16577-1-git-send-email-dwmw@amazon.co.uk>
References: <1516872189-16577-1-git-send-email-dwmw@amazon.co.uk>
Sender: linux-kernel-owner@vger.kernel.org
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Also, for CPUs which don't speculate at all, don't report that they're vulnerable
to the Spectre variants either.

Leave the cpu_no_meltdown[] match table with just X86_VENDOR_AMD in it for now,
even though that could be done with a simple comparison, on the assumption that
we'll have more to add.

Based on suggestions from Dave Hansen and Alan Cox.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kernel/cpu/common.c | 47 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index e5d66e9..08c3efb 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -47,6 +47,8 @@
 #include <asm/pat.h>
 #include <asm/microcode.h>
 #include <asm/microcode_intel.h>
+#include <asm/intel-family.h>
+#include <asm/cpu_device_id.h>
 
 #ifdef CONFIG_X86_LOCAL_APIC
 #include <asm/uv/uv.h>
@@ -853,6 +855,40 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
 #endif
 }
 
+static const __initdata struct x86_cpu_id cpu_no_speculation[] = {
+	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CEDARVIEW, X86_FEATURE_ANY },
+	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CLOVERVIEW, X86_FEATURE_ANY },
+	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_LINCROFT, X86_FEATURE_ANY },
+	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PENWELL, X86_FEATURE_ANY },
+	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PINEVIEW, X86_FEATURE_ANY },
+	{ X86_VENDOR_INTEL, 5 },
+	{ X86_VENDOR_CENTAUR, 5 },
+	{ X86_VENDOR_ANY, 4 },
+	{}
+};
+
+static const __initdata struct x86_cpu_id cpu_no_meltdown[] = {
+	{ X86_VENDOR_AMD },
+	{}
+};
+
+static bool __init early_cpu_vulnerable_meltdown(struct cpuinfo_x86 *c)
+{
+	u64 ia32_cap = 0;
+
+	if (x86_match_cpu(cpu_no_meltdown))
+                return false;
+
+	if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
+		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
+
+	/* Rogue Data Cache Load? No! */
+	if (ia32_cap & ARCH_CAP_RDCL_NO)
+		return false;
+
+	return true;
+}
+
 /*
  * Do minimum CPU detection early.
  * Fields really needed: vendor, cpuid_level, family, model, mask,
@@ -900,11 +936,12 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 
 	setup_force_cpu_cap(X86_FEATURE_ALWAYS);
 
-	if (c->x86_vendor != X86_VENDOR_AMD)
-		setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);
-
-	setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
-	setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
+	if (!x86_match_cpu(cpu_no_speculation)) {
+		if (early_cpu_vulnerable_meltdown(c))
+			setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);
+		setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
+		setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
+	}
 
 	fpu__init_system(c);
 
-- 
2.7.4