[Devel] [PATCH RHEL8 COMMIT] ms/KVM: x86: reinstate vendor-agnostic check on SPEC_CTRL cpuid bits #PSBM-120787 #PSBM-123538

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-240.1.1.vz8.5.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-240.1.1.el8
------>
commit 39074da0597b4d25ec98c688668bc3b063b7647c
Author: Paolo Bonzini <pbonzini at redhat.com>
Date:   Thu Dec 3 10:15:16 2020 -0500

    ms/KVM: x86: reinstate vendor-agnostic check on SPEC_CTRL cpuid bits #PSBM-120787 #PSBM-123538
    
    Until commit e7c587da1252 ("x86/speculation: Use synthetic bits for IBRS/IBPB/STIBP",
    2018-05-17), KVM was testing both Intel and AMD CPUID bits before allowing the
    guest to write MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD.  Testing only Intel bits
    on VMX processors, or only AMD bits on SVM processors, fails if the guests are
    created with the "opposite" vendor as the host.
    
    While at it, also tweak the host CPU check to use the vendor-agnostic feature bit
    X86_FEATURE_IBPB, since we only care about the availability of the MSR on the host
    here and not about specific CPUID bits.
    
    mFixes: e7c587da1252 ("x86/speculation: Use synthetic bits for IBRS/IBPB/STIBP")
    Cc: stable at vger.kernel.org
    Reported-by: Denis V. Lunev <den at openvz.org>
    Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
    
    https://jira.sw.ru/browse/PSBM-123538
    
    ========================================
    The patch is a replacement for vz patch:
    
     commit 39d637ddbcf876f897e01c737bbb351461921df0
     Author: Denis V. Lunev <den at openvz.org>
     Date:   Wed Oct 28 19:25:57 2020 +0300
    
        kvm: fix AMD IBRS/IBPB/STIBP/SSBD reporting #PSBM-120787
    
        We should report these bits in 80000008 EBX on AMD only, i.e. when AMD
        specific feature bits are enabled.
    
        https://jira.sw.ru/browse/PSBM-120787
    
        Signed-off-by: Denis V. Lunev <den at openvz.org>
        CC: Vasily Averin <vvs at virtuozzo.com>
        CC: Konstantin Khorenko <khorenko at virtuozzo.com>
    ========================================
---
 arch/x86/kvm/svm/svm.c |  3 ++-
 arch/x86/kvm/vmx/vmx.c | 10 +++++++---
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 3ea87e4bff90..7c76485f0b6b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2547,12 +2547,13 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		break;
 	case MSR_IA32_PRED_CMD:
 		if (!msr->host_initiated &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
 		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBPB))
 			return 1;
 
 		if (data & ~PRED_CMD_IBPB)
 			return 1;
-		if (!boot_cpu_has(X86_FEATURE_AMD_IBPB))
+		if (!boot_cpu_has(X86_FEATURE_IBPB))
 			return 1;
 		if (!data)
 			break;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 547ef2dd03a7..4411eaf652a6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2058,7 +2058,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		break;
 	case MSR_IA32_SPEC_CTRL:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
+		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_STIBP) &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
 			return 1;
 
 		if (kvm_spec_ctrl_test_value(data))
@@ -2093,12 +2096,13 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		goto find_shared_msr;
 	case MSR_IA32_PRED_CMD:
 		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
+		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBPB))
 			return 1;
 
 		if (data & ~PRED_CMD_IBPB)
 			return 1;
-		if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL))
+		if (!boot_cpu_has(X86_FEATURE_IBPB))
 			return 1;
 		if (!data)
 			break;