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    Subject[PATCH 3.12 069/124] KVM: nSVM: Check for NRIPS support before updating control field
    Date
    From: Bandan Das <bsd@redhat.com>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    commit f104765b4f81fd74d69e0eb161e89096deade2db upstream.

    If hardware doesn't support DecodeAssist - a feature that provides
    more information about the intercept in the VMCB, KVM decodes the
    instruction and then updates the next_rip vmcb control field.
    However, NRIP support itself depends on cpuid Fn8000_000A_EDX[NRIPS].
    Since skip_emulated_instruction() doesn't verify nrip support
    before accepting control.next_rip as valid, avoid writing this
    field if support isn't present.

    Signed-off-by: Bandan Das <bsd@redhat.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    arch/x86/kvm/svm.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
    index 5dcdff58b679..2996635196d3 100644
    --- a/arch/x86/kvm/svm.c
    +++ b/arch/x86/kvm/svm.c
    @@ -495,8 +495,10 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
    {
    struct vcpu_svm *svm = to_svm(vcpu);

    - if (svm->vmcb->control.next_rip != 0)
    + if (svm->vmcb->control.next_rip != 0) {
    + WARN_ON(!static_cpu_has(X86_FEATURE_NRIPS));
    svm->next_rip = svm->vmcb->control.next_rip;
    + }

    if (!svm->next_rip) {
    if (emulate_instruction(vcpu, EMULTYPE_SKIP) !=
    @@ -4237,7 +4239,9 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
    break;
    }

    - vmcb->control.next_rip = info->next_rip;
    + /* TODO: Advertise NRIPS to guest hypervisor unconditionally */
    + if (static_cpu_has(X86_FEATURE_NRIPS))
    + vmcb->control.next_rip = info->next_rip;
    vmcb->control.exit_code = icpt_info.exit_code;
    vmexit = nested_svm_exit_handled(svm);

    --
    2.4.6


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