Re: [PATCH v3 21/34] KVM: nSVM: hyper-v: Enable L2 TLB flush

Maxim Levitsky
2022-05-11T11:34:10Z

On Thu, 2022-04-14 at 15:20 +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 partition 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.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/svm/hyperv.c | 7 +++++++
> arch/x86/kvm/svm/hyperv.h | 19 +++++++++++++++++++
> arch/x86/kvm/svm/nested.c | 22 +++++++++++++++++++++-
> 3 files changed, 47 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/hyperv.c b/arch/x86/kvm/svm/hyperv.c
> index c0749fc282fe..3842548bb88c 100644
> --- a/arch/x86/kvm/svm/hyperv.c
> +++ b/arch/x86/kvm/svm/hyperv.c
> @@ -8,4 +8,11 @@
>
> void svm_post_hv_l2_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 a2b0d7580b0d..cd33e89f9f61 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 +51,22 @@ 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_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 hv_vp_assist_page assist_page;
> +
> + if (unlikely(!kvm_hv_get_assist_page(vcpu, &assist_page)))
> + return false;
> +
> + if (!hve->hv_enlightenments_control.nested_flush_hypercall)
> + return false;
> +
> + return assist_page.nested_control.features.directhypercall;
> +}
> +
> void svm_post_hv_l2_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 de3f27301b5c..a6d9807c09b1 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -172,7 +172,8 @@ void recalc_intercepts(struct vcpu_svm *svm)
> }
>
> /* We don't want to see VMMCALLs from a nested guest */

Minor nitpick: Maybe update the comment?

> - vmcb_clr_intercept(c, INTERCEPT_VMMCALL);
> + 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];
> @@ -488,6 +489,17 @@ 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:
> @@ -1357,6 +1369,7 @@ 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:
> @@ -1375,6 +1388,13 @@ 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 (kvm_hv_l2_tlb_flush_exposed(vcpu) &&
> + nested_svm_l2_tlb_flush_enabled(vcpu) &&
> + kvm_hv_is_tlb_flush_hcall(vcpu))
> + return NESTED_EXIT_HOST;
> + break;
> default:
> break;
> }

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky