[1/2] kvm: x86: Host feature SSBD doesn't imply guest feature SPEC_CTRL_SSBD
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Message ID 20191214001516.137526-1-jmattson@google.com
State New
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  • [1/2] kvm: x86: Host feature SSBD doesn't imply guest feature SPEC_CTRL_SSBD
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Commit Message

Jim Mattson Dec. 14, 2019, 12:15 a.m. UTC
The host reports support for the synthetic feature X86_FEATURE_SSBD
when any of the three following hardware features are set:
  CPUID.(EAX=7,ECX=0):EDX.SSBD[bit 31]
  CPUID.80000008H:EBX.AMD_SSBD[bit 24]
  CPUID.80000008H:EBX.VIRT_SSBD[bit 25]

Either of the first two hardware features implies the existence of the
IA32_SPEC_CTRL MSR, but CPUID.80000008H:EBX.VIRT_SSBD[bit 25] does
not. Therefore, CPUID.(EAX=7,ECX=0):EDX.SSBD[bit 31] should only be
set in the guest if CPUID.(EAX=7,ECX=0):EDX.SSBD[bit 31] or
CPUID.80000008H:EBX.AMD_SSBD[bit 24] is set on the host.

Fixes: 0c54914d0c52a ("KVM: x86: use Intel speculation bugs and features as derived in generic x86 code")
Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Jacob Xu <jacobhxu@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
 arch/x86/kvm/cpuid.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff mbox series

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index cfafa320a8cf..d70a08dec9b6 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -402,7 +402,8 @@  static inline void do_cpuid_7_mask(struct kvm_cpuid_entry2 *entry, int index)
 			entry->edx |= F(SPEC_CTRL);
 		if (boot_cpu_has(X86_FEATURE_STIBP))
 			entry->edx |= F(INTEL_STIBP);
-		if (boot_cpu_has(X86_FEATURE_SSBD))
+		if (boot_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
+		    boot_cpu_has(X86_FEATURE_AMD_SSBD))
 			entry->edx |= F(SPEC_CTRL_SSBD);
 		 * We emulate ARCH_CAPABILITIES in software even