From 6ac2f49edb1ef5446089c7c660017732886d62d6 Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk Date: Fri, 1 Jun 2018 10:59:20 -0400 Subject: x86/bugs: Add AMD's SPEC_CTRL MSR usage MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The AMD document outlining the SSBD handling 124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf mentions that if CPUID 8000_0008.EBX[24] is set we should be using the SPEC_CTRL MSR (0x48) over the VIRT SPEC_CTRL MSR (0xC001_011f) for speculative store bypass disable. This in effect means we should clear the X86_FEATURE_VIRT_SSBD flag so that we would prefer the SPEC_CTRL MSR. See the document titled: 124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf A copy of this document is available at https://bugzilla.kernel.org/show_bug.cgi?id=199889 Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Thomas Gleixner Cc: Tom Lendacky Cc: Janakarajan Natarajan Cc: kvm@vger.kernel.org Cc: KarimAllah Ahmed Cc: andrew.cooper3@citrix.com Cc: Joerg Roedel Cc: Radim Krčmář Cc: Andy Lutomirski Cc: "H. Peter Anvin" Cc: Paolo Bonzini Cc: Borislav Petkov Cc: David Woodhouse Cc: Kees Cook Link: https://lkml.kernel.org/r/20180601145921.9500-3-konrad.wilk@oracle.com --- arch/x86/kvm/cpuid.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'arch/x86/kvm/cpuid.c') diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 132f8a58692e..f4f30d0c25c4 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -379,7 +379,8 @@ 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_SSB_NO); + F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) | + F(AMD_SSB_NO); /* cpuid 0xC0000001.edx */ const u32 kvm_cpuid_C000_0001_edx_x86_features = @@ -664,7 +665,12 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, entry->ebx |= F(VIRT_SSBD); entry->ebx &= kvm_cpuid_8000_0008_ebx_x86_features; cpuid_mask(&entry->ebx, CPUID_8000_0008_EBX); - if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD)) + /* + * The preference is to use SPEC CTRL MSR instead of the + * VIRT_SPEC MSR. + */ + if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) && + !boot_cpu_has(X86_FEATURE_AMD_SSBD)) entry->ebx |= F(VIRT_SSBD); break; } -- cgit v1.2.3