linux-kernel - [PATCH 1/3] KVM: x86: fix reporting of AMD speculation bug CPUID leaf

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Message-Id: <1566376002-17121-2-git-send-email-pbonzini@redhat.com>
Date:   Wed, 21 Aug 2019 10:26:40 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     jmattson@...hat.com, ehabkost@...hat.com, konrad.wilk@...cle.com
Subject: [PATCH 1/3] KVM: x86: fix reporting of AMD speculation bug CPUID leaf

The AMD_* bits have to be set from the vendor-independent
feature and bug flags, because KVM_GET_SUPPORTED_CPUID does not care
about the vendor and they should be set on Intel processors as well.
On top of this, SSBD, STIBP and AMD_SSB_NO bit were not set, and
VIRT_SSBD does not have to be added manually because it is a
cpufeature that comes directly from the host's CPUID bit.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/cpuid.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 22c2720cd948..43caeb6059b9 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -729,18 +729,23 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 			g_phys_as = phys_as;
 		entry->eax = g_phys_as | (virt_as << 8);
 		entry->edx = 0;
+		entry->ebx &= kvm_cpuid_8000_0008_ebx_x86_features;
+		cpuid_mask(&entry->ebx, CPUID_8000_0008_EBX);
 		/*
-		 * IBRS, IBPB and VIRT_SSBD aren't necessarily present in
-		 * hardware cpuid
+		 * AMD has separate bits for each SPEC_CTRL bit.
+		 * arch/x86/kernel/cpu/bugs.c is kind enough to
+		 * record that in cpufeatures so use them.
 		 */
-		if (boot_cpu_has(X86_FEATURE_AMD_IBPB))
+		if (boot_cpu_has(X86_FEATURE_IBPB))
 			entry->ebx |= F(AMD_IBPB);
-		if (boot_cpu_has(X86_FEATURE_AMD_IBRS))
+		if (boot_cpu_has(X86_FEATURE_IBRS))
 			entry->ebx |= F(AMD_IBRS);
-		if (boot_cpu_has(X86_FEATURE_VIRT_SSBD))
-			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_STIBP))
+			entry->ebx |= F(AMD_STIBP);
+		if (boot_cpu_has(X86_FEATURE_SSBD))
+			entry->ebx |= F(AMD_SSBD);
+		if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
+			entry->ebx |= F(AMD_SSB_NO);
 		/*
 		 * The preference is to use SPEC CTRL MSR instead of the
 		 * VIRT_SPEC MSR.
-- 
1.8.3.1