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    Subject[PATCH 5.4 14/47] KVM: x86: reinstate vendor-agnostic check on SPEC_CTRL cpuid bits
    Date
    From: Paolo Bonzini <pbonzini@redhat.com>

    [ Upstream commit 39485ed95d6b83b62fa75c06c2c4d33992e0d971 ]

    Until commit e7c587da1252 ("x86/speculation: Use synthetic bits for
    IBRS/IBPB/STIBP"), 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.

    Fixes: e7c587da1252 ("x86/speculation: Use synthetic bits for IBRS/IBPB/STIBP")
    Cc: stable@vger.kernel.org
    Reported-by: Denis V. Lunev <den@openvz.org>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/x86/kvm/cpuid.h | 14 ++++++++++++++
    arch/x86/kvm/svm.c | 14 ++++----------
    arch/x86/kvm/vmx/vmx.c | 8 ++++----
    3 files changed, 22 insertions(+), 14 deletions(-)

    diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
    index d78a61408243f..7dec43b2c4205 100644
    --- a/arch/x86/kvm/cpuid.h
    +++ b/arch/x86/kvm/cpuid.h
    @@ -154,6 +154,20 @@ static inline int guest_cpuid_stepping(struct kvm_vcpu *vcpu)
    return x86_stepping(best->eax);
    }

    +static inline bool guest_has_spec_ctrl_msr(struct kvm_vcpu *vcpu)
    +{
    + return (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));
    +}
    +
    +static inline bool guest_has_pred_cmd_msr(struct kvm_vcpu *vcpu)
    +{
    + return (guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) ||
    + guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBPB));
    +}
    +
    static inline bool supports_cpuid_fault(struct kvm_vcpu *vcpu)
    {
    return vcpu->arch.msr_platform_info & MSR_PLATFORM_INFO_CPUID_FAULT;
    diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
    index ca746006ac040..2b506904be024 100644
    --- a/arch/x86/kvm/svm.c
    +++ b/arch/x86/kvm/svm.c
    @@ -4233,10 +4233,7 @@ static int svm_get_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_AMD_STIBP) &&
    - !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) &&
    - !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
    + !guest_has_spec_ctrl_msr(vcpu))
    return 1;

    msr_info->data = svm->spec_ctrl;
    @@ -4320,10 +4317,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
    break;
    case MSR_IA32_SPEC_CTRL:
    if (!msr->host_initiated &&
    - !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))
    + !guest_has_spec_ctrl_msr(vcpu))
    return 1;

    if (data & ~kvm_spec_ctrl_valid_bits(vcpu))
    @@ -4348,12 +4342,12 @@ 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_AMD_IBPB))
    + !guest_has_pred_cmd_msr(vcpu))
    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 8450fce70bd96..e7fd2f00edc11 100644
    --- a/arch/x86/kvm/vmx/vmx.c
    +++ b/arch/x86/kvm/vmx/vmx.c
    @@ -1788,7 +1788,7 @@ static int vmx_get_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_has_spec_ctrl_msr(vcpu))
    return 1;

    msr_info->data = to_vmx(vcpu)->spec_ctrl;
    @@ -1971,7 +1971,7 @@ 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_has_spec_ctrl_msr(vcpu))
    return 1;

    if (data & ~kvm_spec_ctrl_valid_bits(vcpu))
    @@ -1999,12 +1999,12 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
    break;
    case MSR_IA32_PRED_CMD:
    if (!msr_info->host_initiated &&
    - !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
    + !guest_has_pred_cmd_msr(vcpu))
    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;
    --
    2.27.0


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