linux-kernel - [PATCH 4.19 29/40] kvm: x86: Host feature SSBD doesnt imply guest feature SPEC_CTRL

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Date:   Mon, 20 Apr 2020 14:39:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        Jacob Xu <jacobhxu@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Eric Biggers <ebiggers@...nel.org>,
        Ben Hutchings <ben@...adent.org.uk>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 29/40] kvm: x86: Host feature SSBD doesnt imply guest feature SPEC_CTRL_SSBD

From: Jim Mattson <jmattson@...gle.com>

commit 396d2e878f92ec108e4293f1c77ea3bc90b414ff 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.(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@...gle.com>
Reviewed-by: Jacob Xu <jacobhxu@...gle.com>
Reviewed-by: Peter Shier <pshier@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Reported-by: Eric Biggers <ebiggers@...nel.org>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
[bwh: Backported to 4.x: adjust indentation]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kvm/cpuid.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 48c24d0e9e75c..1fe9ccabc082a 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -509,7 +509,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 				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
-- 
2.20.1