linux-kernel - [PATCH v1 1/3] x86/bugs: Add AMD's variant of SSB

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Message-Id: <20180601145921.9500-2-konrad.wilk@oracle.com>
Date:   Fri,  1 Jun 2018 10:59:19 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
        tglx@...utronix.de, andrew.cooper3@...rix.com
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Tom Lendacky <thomas.lendacky@....com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v1 1/3] x86/bugs: Add AMD's variant of SSB_NO.

The AMD document outlining the SSBD handling
124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf
mentions that the CPUID 8000_0008.EBX[26] will mean that the
speculative store bypass disable is no longer needed.

A copy of this document is available at
    https://bugzilla.kernel.org/show_bug.cgi?id=199889

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

---
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Borislav Petkov <bp@...e.de>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Janakarajan Natarajan <Janakarajan.Natarajan@....com>
Cc: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kernel/cpu/common.c       | 3 ++-
 arch/x86/kvm/cpuid.c               | 2 +-
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index fb00a2fca990..b6d7ce32927a 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -283,6 +283,7 @@
 #define X86_FEATURE_AMD_IBRS		(13*32+14) /* "" Indirect Branch Restricted Speculation */
 #define X86_FEATURE_AMD_STIBP		(13*32+15) /* "" Single Thread Indirect Branch Predictors */
 #define X86_FEATURE_VIRT_SSBD		(13*32+25) /* Virtualized Speculative Store Bypass Disable */
+#define X86_FEATURE_AMD_SSB_NO		(13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
 
 /* 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/common.c b/arch/x86/kernel/cpu/common.c
index 38276f58d3bf..494735cf63f5 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -972,7 +972,8 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
 		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
 
 	if (!x86_match_cpu(cpu_no_spec_store_bypass) &&
-	   !(ia32_cap & ARCH_CAP_SSB_NO))
+	   !(ia32_cap & ARCH_CAP_SSB_NO) &&
+	   !cpu_has(c, X86_FEATURE_AMD_SSB_NO))
 		setup_force_cpu_bug(X86_BUG_SPEC_STORE_BYPASS);
 
 	if (x86_match_cpu(cpu_no_meltdown))
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 92bf2f2e7cdd..132f8a58692e 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -379,7 +379,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 
 	/* cpuid 0x80000008.ebx */
 	const u32 kvm_cpuid_8000_0008_ebx_x86_features =
-		F(AMD_IBPB) | F(AMD_IBRS) | F(VIRT_SSBD);
+		F(AMD_IBPB) | F(AMD_IBRS) | F(VIRT_SSBD) | F(AMD_SSB_NO);
 
 	/* cpuid 0xC0000001.edx */
 	const u32 kvm_cpuid_C000_0001_edx_x86_features =
-- 
2.13.4