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.

Reviewed-by: Maxim Levitsky <redacted>
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 | 27 +++++++++++++++++++++++++--
 3 files changed, 51 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..6ea78499e21b 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_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 b203e6cd75dc..083b95d85495 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:

@@ -1409,6 +1424,7 @@ 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:

@@ -1427,6 +1443,13 @@ 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;
 	}