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    SubjectRe: [PATCH v7 3/3] KVM: vmx: handle vm-exit for UMWAIT and TPAUSE
    On Fri, Jul 12, 2019 at 04:29:07PM +0800, Tao Xu wrote:
    > --- a/arch/x86/kvm/vmx/nested.c
    > +++ b/arch/x86/kvm/vmx/nested.c
    > @@ -5213,6 +5213,9 @@ bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)
    > case EXIT_REASON_ENCLS:
    > /* SGX is never exposed to L1 */
    > return false;
    > + case EXIT_REASON_UMWAIT: case EXIT_REASON_TPAUSE:

    Grouped case statements are usually stacked vertically, e.g.:

    case EXIT_REASON_UMWAIT:
    case EXIT_REASON_TPAUSE:

    > + return nested_cpu_has2(vmcs12,
    > + SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE);
    > default:
    > return true;
    > }
    > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
    > index 0787f140d155..e026b1313dc3 100644
    > --- a/arch/x86/kvm/vmx/vmx.c
    > +++ b/arch/x86/kvm/vmx/vmx.c
    > @@ -5349,6 +5349,20 @@ static int handle_monitor(struct kvm_vcpu *vcpu)
    > return handle_nop(vcpu);
    > }
    >
    > +static int handle_umwait(struct kvm_vcpu *vcpu)
    > +{
    > + kvm_skip_emulated_instruction(vcpu);
    > + WARN(1, "this should never happen\n");

    Blech. I'm guessing this code was copy-pasted from handle_xsaves() and
    handle_xrstors(). The blurb of "this should never happen" isn't very
    helpful, e.g. the WARN itself makes it pretty obvious that we don't expect
    to reach this point. WARN_ONCE would also be preferable, no need to spam
    the log in the event things go completely haywire.

    Rather than propagate ugly code, what about defining a common helper, e.g.

    static int handle_unexpected_vmexit(struct kvm_vcpu *vcpu)
    {
    kvm_skip_emulated_instruction(vcpu);
    WARN_ONCE(1, "Unexpected VM-Exit = 0x%x", vmcs_read32(VM_EXIT_REASON));
    return 1;
    }

    ...
    {
    [EXIT_REASON_XSAVES] = handle_unexpected_vmexit,
    [EXIT_REASON_XRSTORS] = handle_unexpected_vmexit,

    [EXIT_REASON_UMWAIT] = handle_unexpected_vmexit,
    [EXIT_REASON_TPAUSE] = handle_unexpected_vmexit,

    }

    > + return 1;
    > +}
    > +
    > +static int handle_tpause(struct kvm_vcpu *vcpu)
    > +{
    > + kvm_skip_emulated_instruction(vcpu);
    > + WARN(1, "this should never happen\n");
    > + return 1;
    > +}
    > +
    > static int handle_invpcid(struct kvm_vcpu *vcpu)
    > {
    > u32 vmx_instruction_info;
    > @@ -5559,6 +5573,8 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
    > [EXIT_REASON_VMFUNC] = handle_vmx_instruction,
    > [EXIT_REASON_PREEMPTION_TIMER] = handle_preemption_timer,
    > [EXIT_REASON_ENCLS] = handle_encls,
    > + [EXIT_REASON_UMWAIT] = handle_umwait,
    > + [EXIT_REASON_TPAUSE] = handle_tpause,
    > };
    >
    > static const int kvm_vmx_max_exit_handlers =
    > --
    > 2.20.1
    >

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