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    SubjectRe: [PATCH v2 10/11] KVM: SVM: implement support for vNMI
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    On 11/30/2022 1:07 AM, Maxim Levitsky wrote:
    > This patch implements support for injecting pending
    > NMIs via the .kvm_x86_set_hw_nmi_pending using new AMD's vNMI
    > feature.
    >
    > Note that the vNMI can't cause a VM exit, which is needed
    > when a nested guest intercepts NMIs.
    >
    > Therefore to avoid breaking nesting, the vNMI is inhibited while
    > a nested guest is running and instead, the legacy NMI window
    > detection and delivery method is used.
    >
    > While it is possible to passthrough the vNMI if a nested guest
    > doesn't intercept NMIs, such usage is very uncommon, and it's
    > not worth to optimize for.
    >
    > Signed-off-by: Santosh Shukla <santosh.shukla@amd.com>
    > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
    > ---
    > arch/x86/kvm/svm/nested.c | 42 +++++++++++++++
    > arch/x86/kvm/svm/svm.c | 111 ++++++++++++++++++++++++++++++--------
    > arch/x86/kvm/svm/svm.h | 10 ++++
    > 3 files changed, 140 insertions(+), 23 deletions(-)
    >
    > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
    > index e891318595113e..5bea672bf8b12d 100644
    > --- a/arch/x86/kvm/svm/nested.c
    > +++ b/arch/x86/kvm/svm/nested.c
    > @@ -623,6 +623,42 @@ static bool is_evtinj_nmi(u32 evtinj)
    > return type == SVM_EVTINJ_TYPE_NMI;
    > }
    >
    > +static void nested_svm_save_vnmi(struct vcpu_svm *svm)
    > +{
    > + struct vmcb *vmcb01 = svm->vmcb01.ptr;
    > +
    > + /*
    > + * Copy the vNMI state back to software NMI tracking state
    > + * for the duration of the nested run
    > + */
    > +
    nits - Extra line.

    > + svm->nmi_masked = vmcb01->control.int_ctl & V_NMI_MASK;
    > + svm->vcpu.arch.nmi_pending += vmcb01->control.int_ctl & V_NMI_PENDING;
    > +}
    > +
    > +static void nested_svm_restore_vnmi(struct vcpu_svm *svm)
    > +{
    > + struct kvm_vcpu *vcpu = &svm->vcpu;
    > + struct vmcb *vmcb01 = svm->vmcb01.ptr;
    > +
    > + /*
    > + * Restore the vNMI state from the software NMI tracking state
    > + * after a nested run
    > + */
    > +
    Ditto...

    Thanks,
    Santosh
    > + if (svm->nmi_masked)
    > + vmcb01->control.int_ctl |= V_NMI_MASK;
    > + else
    > + vmcb01->control.int_ctl &= ~V_NMI_MASK;
    > +
    > + if (vcpu->arch.nmi_pending) {
    > + vcpu->arch.nmi_pending--;
    > + vmcb01->control.int_ctl |= V_NMI_PENDING;
    > + } else
    > + vmcb01->control.int_ctl &= ~V_NMI_PENDING;
    > +}
    > +
    > +
    > static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
    > unsigned long vmcb12_rip,
    > unsigned long vmcb12_csbase)
    > @@ -646,6 +682,9 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
    > else
    > int_ctl_vmcb01_bits |= (V_GIF_MASK | V_GIF_ENABLE_MASK);
    >
    > + if (vnmi)
    > + nested_svm_save_vnmi(svm);
    > +
    > /* Copied from vmcb01. msrpm_base can be overwritten later. */
    > vmcb02->control.nested_ctl = vmcb01->control.nested_ctl;
    > vmcb02->control.iopm_base_pa = vmcb01->control.iopm_base_pa;
    > @@ -1049,6 +1088,9 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
    > svm_update_lbrv(vcpu);
    > }
    >
    > + if (vnmi)
    > + nested_svm_restore_vnmi(svm);
    > +
    > /*
    > * On vmexit the GIF is set to false and
    > * no event can be injected in L1.
    > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
    > index cfed6ab29c839a..bf10adcf3170a8 100644
    > --- a/arch/x86/kvm/svm/svm.c
    > +++ b/arch/x86/kvm/svm/svm.c
    > @@ -230,6 +230,8 @@ module_param(dump_invalid_vmcb, bool, 0644);
    > bool intercept_smi = true;
    > module_param(intercept_smi, bool, 0444);
    >
    > +bool vnmi = true;
    > +module_param(vnmi, bool, 0444);
    >
    > static bool svm_gp_erratum_intercept = true;
    >
    > @@ -1299,6 +1301,9 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
    > if (kvm_vcpu_apicv_active(vcpu))
    > avic_init_vmcb(svm, vmcb);
    >
    > + if (vnmi)
    > + svm->vmcb->control.int_ctl |= V_NMI_ENABLE;
    > +
    > if (vgif) {
    > svm_clr_intercept(svm, INTERCEPT_STGI);
    > svm_clr_intercept(svm, INTERCEPT_CLGI);
    > @@ -3487,6 +3492,39 @@ static void svm_inject_nmi(struct kvm_vcpu *vcpu)
    > ++vcpu->stat.nmi_injections;
    > }
    >
    > +
    > +static bool svm_get_hw_nmi_pending(struct kvm_vcpu *vcpu)
    > +{
    > + struct vcpu_svm *svm = to_svm(vcpu);
    > +
    > + if (!is_vnmi_enabled(svm))
    > + return false;
    > +
    > + return !!(svm->vmcb->control.int_ctl & V_NMI_MASK);
    > +}
    > +
    > +static bool svm_set_hw_nmi_pending(struct kvm_vcpu *vcpu)
    > +{
    > + struct vcpu_svm *svm = to_svm(vcpu);
    > +
    > + if (!is_vnmi_enabled(svm))
    > + return false;
    > +
    > + if (svm->vmcb->control.int_ctl & V_NMI_PENDING)
    > + return false;
    > +
    > + svm->vmcb->control.int_ctl |= V_NMI_PENDING;
    > + vmcb_mark_dirty(svm->vmcb, VMCB_INTR);
    > +
    > + /*
    > + * NMI isn't yet technically injected but
    > + * this rough estimation should be good enough
    > + */
    > + ++vcpu->stat.nmi_injections;
    > +
    > + return true;
    > +}
    > +
    > static void svm_inject_irq(struct kvm_vcpu *vcpu, bool reinjected)
    > {
    > struct vcpu_svm *svm = to_svm(vcpu);
    > @@ -3582,11 +3620,38 @@ static void svm_update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
    > svm_set_intercept(svm, INTERCEPT_CR8_WRITE);
    > }
    >
    > +static bool svm_get_nmi_mask(struct kvm_vcpu *vcpu)
    > +{
    > + struct vcpu_svm *svm = to_svm(vcpu);
    > +
    > + if (is_vnmi_enabled(svm))
    > + return svm->vmcb->control.int_ctl & V_NMI_MASK;
    > + else
    > + return svm->nmi_masked;
    > +}
    > +
    > +static void svm_set_nmi_mask(struct kvm_vcpu *vcpu, bool masked)
    > +{
    > + struct vcpu_svm *svm = to_svm(vcpu);
    > +
    > + if (is_vnmi_enabled(svm)) {
    > + if (masked)
    > + svm->vmcb->control.int_ctl |= V_NMI_MASK;
    > + else
    > + svm->vmcb->control.int_ctl &= ~V_NMI_MASK;
    > + } else {
    > + svm->nmi_masked = masked;
    > + if (masked)
    > + svm_enable_iret_interception(svm);
    > + else
    > + svm_disable_iret_interception(svm);
    > + }
    > +}
    > +
    > bool svm_nmi_blocked(struct kvm_vcpu *vcpu)
    > {
    > struct vcpu_svm *svm = to_svm(vcpu);
    > struct vmcb *vmcb = svm->vmcb;
    > - bool ret;
    >
    > if (!gif_set(svm))
    > return true;
    > @@ -3594,10 +3659,10 @@ bool svm_nmi_blocked(struct kvm_vcpu *vcpu)
    > if (is_guest_mode(vcpu) && nested_exit_on_nmi(svm))
    > return false;
    >
    > - ret = (vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK) ||
    > - (svm->nmi_masked);
    > + if (svm_get_nmi_mask(vcpu))
    > + return true;
    >
    > - return ret;
    > + return vmcb->control.int_state & SVM_INTERRUPT_SHADOW_MASK;
    > }
    >
    > static int svm_nmi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
    > @@ -3615,24 +3680,6 @@ static int svm_nmi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
    > return 1;
    > }
    >
    > -static bool svm_get_nmi_mask(struct kvm_vcpu *vcpu)
    > -{
    > - return to_svm(vcpu)->nmi_masked;
    > -}
    > -
    > -static void svm_set_nmi_mask(struct kvm_vcpu *vcpu, bool masked)
    > -{
    > - struct vcpu_svm *svm = to_svm(vcpu);
    > -
    > - if (masked) {
    > - svm->nmi_masked = true;
    > - svm_enable_iret_interception(svm);
    > - } else {
    > - svm->nmi_masked = false;
    > - svm_disable_iret_interception(svm);
    > - }
    > -}
    > -
    > bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
    > {
    > struct vcpu_svm *svm = to_svm(vcpu);
    > @@ -3725,10 +3772,16 @@ static void svm_enable_nmi_window(struct kvm_vcpu *vcpu)
    > /*
    > * Something prevents NMI from been injected. Single step over possible
    > * problem (IRET or exception injection or interrupt shadow)
    > + *
    > + * With vNMI we should never need an NMI window
    > + * (we can always inject vNMI either by setting VNMI_PENDING or by EVENTINJ)
    > */
    > + if (WARN_ON_ONCE(is_vnmi_enabled(svm)))
    > + return;
    > +
    > svm->nmi_singlestep_guest_rflags = svm_get_rflags(vcpu);
    > - svm->nmi_singlestep = true;
    > svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
    > + svm->nmi_singlestep = true;
    > }
    >
    > static void svm_flush_tlb_current(struct kvm_vcpu *vcpu)
    > @@ -4770,6 +4823,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
    > .patch_hypercall = svm_patch_hypercall,
    > .inject_irq = svm_inject_irq,
    > .inject_nmi = svm_inject_nmi,
    > + .get_hw_nmi_pending = svm_get_hw_nmi_pending,
    > + .set_hw_nmi_pending = svm_set_hw_nmi_pending,
    > .inject_exception = svm_inject_exception,
    > .cancel_injection = svm_cancel_injection,
    > .interrupt_allowed = svm_interrupt_allowed,
    > @@ -5058,6 +5113,16 @@ static __init int svm_hardware_setup(void)
    > pr_info("Virtual GIF supported\n");
    > }
    >
    > +
    > + vnmi = vgif && vnmi && boot_cpu_has(X86_FEATURE_AMD_VNMI);
    > + if (vnmi)
    > + pr_info("Virtual NMI enabled\n");
    > +
    > + if (!vnmi) {
    > + svm_x86_ops.get_hw_nmi_pending = NULL;
    > + svm_x86_ops.set_hw_nmi_pending = NULL;
    > + }
    > +
    > if (lbrv) {
    > if (!boot_cpu_has(X86_FEATURE_LBRV))
    > lbrv = false;
    > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
    > index 587ddc150f9f34..0b7e1790fadde1 100644
    > --- a/arch/x86/kvm/svm/svm.h
    > +++ b/arch/x86/kvm/svm/svm.h
    > @@ -35,6 +35,7 @@ extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
    > extern bool npt_enabled;
    > extern int vgif;
    > extern bool intercept_smi;
    > +extern bool vnmi;
    >
    > enum avic_modes {
    > AVIC_MODE_NONE = 0,
    > @@ -553,6 +554,15 @@ static inline bool is_x2apic_msrpm_offset(u32 offset)
    > (msr < (APIC_BASE_MSR + 0x100));
    > }
    >
    > +static inline bool is_vnmi_enabled(struct vcpu_svm *svm)
    > +{
    > + /* L1's vNMI is inhibited while nested guest is running */
    > + if (is_guest_mode(&svm->vcpu))
    > + return false;
    > +
    > + return !!(svm->vmcb01.ptr->control.int_ctl & V_NMI_ENABLE);
    > +}
    > +
    > /* svm.c */
    > #define MSR_INVALID 0xffffffffU
    >

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