[PATCH 5.4 417/434] kvm: x86: Host feature SSBD doesnt imply guest feature AMD_SSBD

Greg Kroah-Hartman
2019-12-29T17:58:26Z

From: Jim Mattson <jmattson@google.com>

commit 8715f05269bfbc6453e25e80825d781a82902f8e upstream.

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.80000008H:EBX.AMD_SSBD[bit 24] 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: 4c6903a0f9d76 ("KVM: x86: fix reporting of AMD speculation bug CPUID leaf")
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>
Cc: stable@vger.kernel.org
Reported-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/cpuid.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -760,7 +760,8 @@ static inline int __do_cpuid_func(struct
entry->ebx |= F(AMD_IBRS);
if (boot_cpu_has(X86_FEATURE_STIBP))
entry->ebx |= F(AMD_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->ebx |= F(AMD_SSBD);
if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
entry->ebx |= F(AMD_SSB_NO);