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    SubjectRe: [PATCH v5 07/34] KVM: SVM: Add required changes to support intercepts under SEV-ES
    Date
    On 10/12/20 18:09, Tom Lendacky wrote:
    > @@ -2797,7 +2838,27 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
    >
    > static int wrmsr_interception(struct vcpu_svm *svm)
    > {
    > - return kvm_emulate_wrmsr(&svm->vcpu);
    > + u32 ecx;
    > + u64 data;
    > +
    > + if (!sev_es_guest(svm->vcpu.kvm))
    > + return kvm_emulate_wrmsr(&svm->vcpu);
    > +
    > + ecx = kvm_rcx_read(&svm->vcpu);
    > + data = kvm_read_edx_eax(&svm->vcpu);
    > + if (kvm_set_msr(&svm->vcpu, ecx, data)) {
    > + trace_kvm_msr_write_ex(ecx, data);
    > + ghcb_set_sw_exit_info_1(svm->ghcb, 1);
    > + ghcb_set_sw_exit_info_2(svm->ghcb,
    > + X86_TRAP_GP |
    > + SVM_EVTINJ_TYPE_EXEPT |
    > + SVM_EVTINJ_VALID);
    > + return 1;
    > + }
    > +
    > + trace_kvm_msr_write(ecx, data);
    > +
    > + return kvm_skip_emulated_instruction(&svm->vcpu);
    > }
    >
    > static int msr_interception(struct vcpu_svm *svm)

    This code duplication is ugly, and does not work with userspace MSR
    filters too.

    But we can instead trap the completion of the MSR read/write to use
    ghcb_set_sw_exit_info_1 instead of kvm_inject_gp, with a callback like

    static int svm_complete_emulated_msr(struct kvm_vcpu *vcpu, int err)
    {
    if (!sev_es_guest(svm->vcpu.kvm) || !err)
    return kvm_complete_insn_gp(&svm->vcpu, err);

    ghcb_set_sw_exit_info_1(svm->ghcb, 1);
    ghcb_set_sw_exit_info_2(svm->ghcb,
    X86_TRAP_GP |
    SVM_EVTINJ_TYPE_EXEPT |
    SVM_EVTINJ_VALID);
    return 1;
    }


    ...
    .complete_emulated_msr = svm_complete_emulated_msr,

    > @@ -2827,7 +2888,14 @@ static int interrupt_window_interception(struct vcpu_svm *svm)
    > static int pause_interception(struct vcpu_svm *svm)
    > {
    > struct kvm_vcpu *vcpu = &svm->vcpu;
    > - bool in_kernel = (svm_get_cpl(vcpu) == 0);
    > + bool in_kernel;
    > +
    > + /*
    > + * CPL is not made available for an SEV-ES guest, so just set in_kernel
    > + * to true.
    > + */
    > + in_kernel = (sev_es_guest(svm->vcpu.kvm)) ? true
    > + : (svm_get_cpl(vcpu) == 0);
    >
    > if (!kvm_pause_in_guest(vcpu->kvm))
    > grow_ple_window(vcpu);

    See below.

    > @@ -3273,6 +3351,13 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
    > struct vcpu_svm *svm = to_svm(vcpu);
    > struct vmcb *vmcb = svm->vmcb;
    >
    > + /*
    > + * SEV-ES guests to not expose RFLAGS. Use the VMCB interrupt mask
    > + * bit to determine the state of the IF flag.
    > + */
    > + if (sev_es_guest(svm->vcpu.kvm))
    > + return !(vmcb->control.int_state & SVM_GUEST_INTERRUPT_MASK);

    This seems wrong, you have to take into account
    SVM_INTERRUPT_SHADOW_MASK as well. Also, even though GIF is not really
    used by SEV-ES guests, I think it's nicer to put this check afterwards.

    That is:

    diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
    index 4372e45c8f06..2dd9c9698480 100644
    --- a/arch/x86/kvm/svm/svm.c
    +++ b/arch/x86/kvm/svm/svm.c
    @@ -3247,7 +3247,14 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
    if (!gif_set(svm))
    return true;

    - if (is_guest_mode(vcpu)) {
    + if (sev_es_guest(svm->vcpu.kvm)) {
    + /*
    + * SEV-ES guests to not expose RFLAGS. Use the VMCB interrupt mask
    + * bit to determine the state of the IF flag.
    + */
    + if (!(vmcb->control.int_state & SVM_GUEST_INTERRUPT_MASK))
    + return true;
    + } else if (is_guest_mode(vcpu)) {
    /* As long as interrupts are being delivered... */
    if ((svm->nested.ctl.int_ctl & V_INTR_MASKING_MASK)
    ? !(svm->nested.hsave->save.rflags & X86_EFLAGS_IF)


    > if (!gif_set(svm))
    > return true;
    >
    > @@ -3458,6 +3543,12 @@ static void svm_complete_interrupts(struct vcpu_svm *svm)
    > svm->vcpu.arch.nmi_injected = true;
    > break;
    > case SVM_EXITINTINFO_TYPE_EXEPT:
    > + /*
    > + * Never re-inject a #VC exception.
    > + */
    > + if (vector == X86_TRAP_VC)
    > + break;
    > +
    > /*
    > * In case of software exceptions, do not reinject the vector,
    > * but re-execute the instruction instead. Rewind RIP first
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index a3fdc16cfd6f..b6809a2851d2 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -4018,7 +4018,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
    > {
    > int idx;
    >
    > - if (vcpu->preempted)
    > + if (vcpu->preempted && !vcpu->arch.guest_state_protected)
    > vcpu->arch.preempted_in_kernel = !kvm_x86_ops.get_cpl(vcpu);

    This has to be true, otherwise no directed yield will be done at all:

    if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
    !kvm_arch_vcpu_in_kernel(vcpu))
    continue;
    Or more easily, just use in_kernel == false in pause_interception, like

    + /*
    + * CPL is not made available for an SEV-ES guest, therefore
    + * vcpu->arch.preempted_in_kernel can never be true. Just
    + * set in_kernel to false as well.
    + */
    + in_kernel = !sev_es_guest(svm->vcpu.kvm) && svm_get_cpl(vcpu) == 0;
    >
    > /*
    > @@ -8161,7 +8161,9 @@ static void post_kvm_run_save(struct kvm_vcpu *vcpu)
    > {
    > struct kvm_run *kvm_run = vcpu->run;
    >
    > - kvm_run->if_flag = (kvm_get_rflags(vcpu) & X86_EFLAGS_IF) != 0;
    > + kvm_run->if_flag = (vcpu->arch.guest_state_protected)
    > + ? kvm_arch_interrupt_allowed(vcpu)
    > + : (kvm_get_rflags(vcpu) & X86_EFLAGS_IF) != 0;

    Here indeed you only want the interrupt allowed bit, not the interrupt
    window. But we can just be bold and always set it to true.

    - for userspace irqchip, kvm_run->ready_for_interrupt_injection is set
    just below and it will always be false if kvm_arch_interrupt_allowed is
    false

    - for in-kernel APIC, if_flag is documented to be invalid (though it
    actually is valid). For split irqchip, they can just use
    kvm_run->ready_for_interrupt_injection; for entirely in-kernel interrupt
    handling, userspace does not need if_flag at all.

    Paolo

    > kvm_run->flags = is_smm(vcpu) ? KVM_RUN_X86_SMM : 0;
    > kvm_run->cr8 = kvm_get_cr8(vcpu);
    > kvm_run->apic_base = kvm_get_apic_base(vcpu);
    >


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