[tip:x86/pti] x86/bugs: Add AMD's variant of SSB_NO

[tip-bot for Konrad Rzeszutek Wilk <tipbot@zytor.com>]

Commit-ID:  24809860012e0130fbafe536709e08a22b3e959e
Gitweb:     https://git.kernel.org/tip/24809860012e0130fbafe536709e08a22b3e959e
Author:     Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
AuthorDate: Fri, 1 Jun 2018 10:59:19 -0400
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 6 Jun 2018 14:13:16 +0200

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@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
Cc: kvm@vger.kernel.org
Cc: andrew.cooper3@citrix.com
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lkml.kernel.org/r/20180601145921.9500-2-konrad.wilk@oracle.com

---
 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 95c8e507580d..8e3f062f462d 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -992,7 +992,8 @@ 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 =