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    SubjectRe: [9/8] KVM: x86: limit MSR_IA32_SPEC_CTRL access based on CPUID availability
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    On 30.01.2018 18:33, Jim Mattson wrote:
    > All MSR intercepts are enabled by default, so I don't think this patch
    > does anything at all, unless I'm missing some context.
    >

    Currently on upstream some MSR are intercepted:
    https://github.com/torvalds/linux/blob/master/arch/x86/kvm/vmx.c#L6838

    In particular to this patch, the MSR_IA32_SPEC_CTRL intercept is
    disabled in 3/8: https://patchwork.kernel.org/patch/10151889/


    > On Tue, Jan 30, 2018 at 5:21 AM, Mihai Carabas <mihai.carabas@oracle.com> wrote:
    >> Hello Paolo,
    >>
    >> I've back ported this patch on 4.1, after adding the per-vcpu MSR bitmap.
    >> Also enabled the SPEC_CTRL_MSR intercept if qemu instructed so [1].
    >>
    >> Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
    >>
    >> [1]
    >> +++ b/arch/x86/kvm/vmx.c
    >> @@ -8391,6 +8391,16 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm
    >> *kvm, unsigned int id)
    >> vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PRED_CMD,
    >> MSR_TYPE_R | MSR_TYPE_W);
    >> vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_BNDCFGS,
    >> MSR_TYPE_R | MSR_TYPE_W);
    >>
    >> + /*
    >> + * If the physical CPU or the vCPU of this VM doesn't
    >> + * support SPEC_CTRL feature, catch each access to it.
    >> + */
    >> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
    >> + !guest_cpuid_has_spec_ctrl(&vmx->vcpu))
    >> + vmx_enable_intercept_for_msr(
    >> + msr_bitmap,
    >> + MSR_IA32_SPEC_CTRL,
    >> + MSR_TYPE_R | MSR_TYPE_W);
    >>
    >> /*
    >> * If PML is turned on, failure on enabling PML just results in
    >> failure
    >>
    >>
    >>
    >> On 09.01.2018 14:03, Paolo Bonzini wrote:
    >>>
    >>> MSR_IA32_SPEC_CTRL is not available unless CPU[7,0].EDX[26] is 1.
    >>> Check that against host CPUID or guest CPUID, respectively for
    >>> host-initiated and guest-initiated accesses.
    >>>
    >>> Suggested-by: Jim Mattson <jmattson@google.com>
    >>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    >>> ---
    >>> This is for after X86_FEATURE_SPEC_CTRL is added to Linux, but
    >>> I still wanted to ack Jim's improvement.
    >>>
    >>> arch/x86/kvm/svm.c | 8 ++++++++
    >>> arch/x86/kvm/vmx.c | 8 ++++++++
    >>> 2 files changed, 16 insertions(+)
    >>>
    >>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
    >>> index 97126c2bd663..3a646580d7c5 100644
    >>> --- a/arch/x86/kvm/svm.c
    >>> +++ b/arch/x86/kvm/svm.c
    >>> @@ -3648,6 +3648,10 @@ static int svm_get_msr(struct kvm_vcpu *vcpu,
    >>> struct msr_data *msr_info)
    >>> msr_info->data = svm->nested.vm_cr_msr;
    >>> break;
    >>> case MSR_IA32_SPEC_CTRL:
    >>> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
    >>> + (!msr_info->host_initiated &&
    >>> + !guest_cpuid_has(vcpu,
    >>> X86_FEATURE_SPEC_CTRL)))
    >>> + return 1;
    >>> msr_info->data = svm->spec_ctrl;
    >>> break;
    >>> case MSR_IA32_UCODE_REV:
    >>> @@ -3806,6 +3810,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu,
    >>> struct msr_data *msr)
    >>> vcpu_unimpl(vcpu, "unimplemented wrmsr: 0x%x data
    >>> 0x%llx\n", ecx, data);
    >>> break;
    >>> case MSR_IA32_SPEC_CTRL:
    >>> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
    >>> + (!msr_info->host_initiated &&
    >>> + !guest_cpuid_has(vcpu,
    >>> X86_FEATURE_SPEC_CTRL)))
    >>> + return 1;
    >>> svm->spec_ctrl = data;
    >>> break;
    >>> case MSR_IA32_APICBASE:
    >>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
    >>> index 49b4a2d61603..42bc7ee293e4 100644
    >>> --- a/arch/x86/kvm/vmx.c
    >>> +++ b/arch/x86/kvm/vmx.c
    >>> @@ -3368,6 +3368,10 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu,
    >>> struct msr_data *msr_info)
    >>> msr_info->data = guest_read_tsc(vcpu);
    >>> break;
    >>> case MSR_IA32_SPEC_CTRL:
    >>> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
    >>> + (!msr_info->host_initiated &&
    >>> + !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
    >>> + return 1;
    >>> msr_info->data = to_vmx(vcpu)->spec_ctrl;
    >>> break;
    >>> case MSR_IA32_SYSENTER_CS:
    >>> @@ -3510,6 +3514,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu,
    >>> struct msr_data *msr_info)
    >>> kvm_write_tsc(vcpu, msr_info);
    >>> break;
    >>> case MSR_IA32_SPEC_CTRL:
    >>> + if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
    >>> + (!msr_info->host_initiated &&
    >>> + !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
    >>> + return 1;
    >>> to_vmx(vcpu)->spec_ctrl = data;
    >>> break;
    >>> case MSR_IA32_CR_PAT:
    >>>
    >>

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