Re: [PATCH v6 22/38] KVM: nSVM: hyper-v: Enable L2 TLB flush
From: Maxim Levitsky
Date: Tue Jun 07 2022 - 06:03:07 EST
On Mon, 2022-06-06 at 10:36 +0200, Vitaly Kuznetsov wrote:
> Implement Hyper-V L2 TLB flush for nSVM. The feature needs to be enabled
> both in extended 'nested controls' in VMCB and VP assist page.
> According to Hyper-V TLFS, synthetic vmexit to L1 is performed with
> - HV_SVM_EXITCODE_ENL exit_code.
> - HV_SVM_ENL_EXITCODE_TRAP_AFTER_FLUSH exit_info_1.
>
> Note: VP assist page is cached in 'struct kvm_vcpu_hv' so
> recalc_intercepts() doesn't need to read from guest's memory. KVM
> needs to update the case upon each VMRUN and after svm_set_nested_state
> (svm_get_nested_state_pages()) to handle the case when the guest got
> migrated while L2 was running.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
> arch/x86/kvm/svm/hyperv.c | 7 +++++++
> arch/x86/kvm/svm/hyperv.h | 30 ++++++++++++++++++++++++++++++
> arch/x86/kvm/svm/nested.c | 36 ++++++++++++++++++++++++++++++++++--
> 3 files changed, 71 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/hyperv.c b/arch/x86/kvm/svm/hyperv.c
> index 911f51021af1..088f6429b24c 100644
> --- a/arch/x86/kvm/svm/hyperv.c
> +++ b/arch/x86/kvm/svm/hyperv.c
> @@ -8,4 +8,11 @@
>
> void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu)
> {
> + struct vcpu_svm *svm = to_svm(vcpu);
> +
> + svm->vmcb->control.exit_code = HV_SVM_EXITCODE_ENL;
> + svm->vmcb->control.exit_code_hi = 0;
> + svm->vmcb->control.exit_info_1 = HV_SVM_ENL_EXITCODE_TRAP_AFTER_FLUSH;
> + svm->vmcb->control.exit_info_2 = 0;
> + nested_svm_vmexit(svm);
> }
> diff --git a/arch/x86/kvm/svm/hyperv.h b/arch/x86/kvm/svm/hyperv.h
> index dd2e393f84a0..7b01722838bf 100644
> --- a/arch/x86/kvm/svm/hyperv.h
> +++ b/arch/x86/kvm/svm/hyperv.h
> @@ -33,6 +33,9 @@ struct hv_enlightenments {
> */
> #define VMCB_HV_NESTED_ENLIGHTENMENTS VMCB_SW
>
> +#define HV_SVM_EXITCODE_ENL 0xF0000000
> +#define HV_SVM_ENL_EXITCODE_TRAP_AFTER_FLUSH (1)
> +
> static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
> @@ -48,6 +51,33 @@ static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu)
> hv_vcpu->nested.vp_id = hve->hv_vp_id;
> }
>
> +static inline bool nested_svm_hv_update_vp_assist(struct kvm_vcpu *vcpu)
> +{
> + if (!to_hv_vcpu(vcpu))
> + return true;
> +
> + if (!kvm_hv_assist_page_enabled(vcpu))
> + return true;
> +
> + return kvm_hv_get_assist_page(vcpu);
> +}
> +
> +static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu)
> +{
> + struct vcpu_svm *svm = to_svm(vcpu);
> + struct hv_enlightenments *hve =
> + (struct hv_enlightenments *)svm->nested.ctl.reserved_sw;
> + struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> +
> + if (!hv_vcpu)
> + return false;
> +
> + if (!hve->hv_enlightenments_control.nested_flush_hypercall)
> + return false;
> +
> + return hv_vcpu->vp_assist_page.nested_control.features.directhypercall;
> +}
> +
> void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu);
>
> #endif /* __ARCH_X86_KVM_SVM_HYPERV_H__ */
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 28b63663e1d9..369b92aaf1ad 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -171,8 +171,12 @@ void recalc_intercepts(struct vcpu_svm *svm)
> vmcb_clr_intercept(c, INTERCEPT_VINTR);
> }
>
> - /* We don't want to see VMMCALLs from a nested guest */
> - vmcb_clr_intercept(c, INTERCEPT_VMMCALL);
> + /*
> + * We want to see VMMCALLs from a nested guest only when Hyper-V L2 TLB
> + * flush feature is enabled.
> + */
> + if (!nested_svm_l2_tlb_flush_enabled(&svm->vcpu))
> + vmcb_clr_intercept(c, INTERCEPT_VMMCALL);
>
> for (i = 0; i < MAX_INTERCEPT; i++)
> c->intercepts[i] |= g->intercepts[i];
> @@ -489,6 +493,17 @@ static void nested_save_pending_event_to_vmcb12(struct vcpu_svm *svm,
>
> static void nested_svm_transition_tlb_flush(struct kvm_vcpu *vcpu)
> {
> + /*
> + * KVM_REQ_HV_TLB_FLUSH flushes entries from either L1's VP_ID or
> + * L2's VP_ID upon request from the guest. Make sure we check for
> + * pending entries for the case when the request got misplaced (e.g.
> + * a transition from L2->L1 happened while processing L2 TLB flush
> + * request or vice versa). kvm_hv_vcpu_flush_tlb() will not flush
> + * anything if there are no requests in the corresponding buffer.
> + */
> + if (to_hv_vcpu(vcpu))
> + kvm_make_request(KVM_REQ_HV_TLB_FLUSH, vcpu);
> +
> /*
> * TODO: optimize unconditional TLB flush/MMU sync. A partial list of
> * things to fix before this can be conditional:
> @@ -835,6 +850,12 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> + /* This fails when VP assist page is enabled but the supplied GPA is bogus */
> + if (!nested_svm_hv_update_vp_assist(vcpu)) {
> + kvm_inject_gp(vcpu, 0);
> + return 1;
> + }
> +
> vmcb12_gpa = svm->vmcb->save.rax;
> ret = kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map);
> if (ret == -EINVAL) {
> @@ -1412,6 +1433,7 @@ static int svm_check_nested_events(struct kvm_vcpu *vcpu)
> int nested_svm_exit_special(struct vcpu_svm *svm)
> {
> u32 exit_code = svm->vmcb->control.exit_code;
> + struct kvm_vcpu *vcpu = &svm->vcpu;
>
> switch (exit_code) {
> case SVM_EXIT_INTR:
> @@ -1430,6 +1452,13 @@ int nested_svm_exit_special(struct vcpu_svm *svm)
> return NESTED_EXIT_HOST;
> break;
> }
> + case SVM_EXIT_VMMCALL:
> + /* Hyper-V L2 TLB flush hypercall is handled by L0 */
> + if (guest_hv_cpuid_has_l2_tlb_flush(vcpu) &&
> + nested_svm_l2_tlb_flush_enabled(vcpu) &&
> + kvm_hv_is_tlb_flush_hcall(vcpu))
> + return NESTED_EXIT_HOST;
> + break;
> default:
> break;
> }
> @@ -1710,6 +1739,9 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
> return false;
> }
>
> + if (!nested_svm_hv_update_vp_assist(vcpu))
> + return false;
> +
> return true;
> }
>
Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Best regards,
Maxim Levitsky