[2/2] kvm: x86: Host feature SSBD doesn't imply guest feature AMD_SSBD
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Message ID 20191214001516.137526-2-jmattson@google.com
State New
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Series
  • [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.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>
---
 arch/x86/kvm/cpuid.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Paolo Bonzini Dec. 18, 2019, 4:46 p.m. UTC | #1
On 14/12/19 01:15, Jim Mattson wrote:
> [...]
Queued both, thanks.

Paolo

Patch
diff mbox series

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index d70a08dec9b6..cf55629ff0ff 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -760,7 +760,8 @@  static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 			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);