[PATCH RFC 16/19] KVM: nVMX: hyper-v: Direct TLB flush

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Enable Direct TLB flush feature on nVMX when:
- Enlightened VMCS is in use.
- Direct TLB flush flag is enabled in eVMCS.
- Direct TLB flush is enabled in partition assist page.

Perform synthetic vmexit to L1 after processing TLB flush call upon
request (HV_VMX_SYNTHETIC_EXIT_REASON_TRAP_AFTER_FLUSH).

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/vmx/evmcs.c  | 20 ++++++++++++++++++++
 arch/x86/kvm/vmx/evmcs.h  |  3 +++
 arch/x86/kvm/vmx/nested.c | 16 ++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
index 1705c4973636..cdf7ec5cb64c 100644
--- a/arch/x86/kvm/vmx/evmcs.c
+++ b/arch/x86/kvm/vmx/evmcs.c
@@ -6,6 +6,7 @@
 #include "../hyperv.h"
 #include "../cpuid.h"
 #include "evmcs.h"
+#include "nested.h"
 #include "vmcs.h"
 #include "vmx.h"
 #include "trace.h"
@@ -438,6 +439,25 @@ int nested_enable_evmcs(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+bool nested_evmcs_direct_flush_enabled(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct hv_enlightened_vmcs *evmcs = vmx->nested.hv_evmcs;
+	struct hv_vp_assist_page assist_page;
+
+	if (!evmcs)
+		return false;
+
+	if (!evmcs->hv_enlightenments_control.nested_flush_hypercall)
+		return false;
+
+	if (unlikely(!kvm_hv_get_assist_page(vcpu, &assist_page)))
+		return false;
+
+	return assist_page.nested_control.features.directhypercall;
+}
+
 void vmx_post_hv_direct_flush(struct kvm_vcpu *vcpu)
 {
+	nested_vmx_vmexit(vcpu, HV_VMX_SYNTHETIC_EXIT_REASON_TRAP_AFTER_FLUSH, 0, 0);
 }
diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
index 8862692a4c5d..ab0949c22d2d 100644
--- a/arch/x86/kvm/vmx/evmcs.h
+++ b/arch/x86/kvm/vmx/evmcs.h
@@ -65,6 +65,8 @@ DECLARE_STATIC_KEY_FALSE(enable_evmcs);
 #define EVMCS1_UNSUPPORTED_VMENTRY_CTRL (VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL)
 #define EVMCS1_UNSUPPORTED_VMFUNC (VMX_VMFUNC_EPTP_SWITCHING)
 
+#define HV_VMX_SYNTHETIC_EXIT_REASON_TRAP_AFTER_FLUSH 0x10000031
+
 struct evmcs_field {
 	u16 offset;
 	u16 clean_field;
@@ -244,6 +246,7 @@ int nested_enable_evmcs(struct kvm_vcpu *vcpu,
 			uint16_t *vmcs_version);
 void nested_evmcs_filter_control_msr(u32 msr_index, u64 *pdata);
 int nested_evmcs_check_controls(struct vmcs12 *vmcs12);
+bool nested_evmcs_direct_flush_enabled(struct kvm_vcpu *vcpu);
 void vmx_post_hv_direct_flush(struct kvm_vcpu *vcpu);
 
 #endif /* __KVM_X86_VMX_EVMCS_H */
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index a9fb6c63f849..3f908a8e5113 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1168,6 +1168,17 @@ static void nested_vmx_transition_tlb_flush(struct kvm_vcpu *vcpu,
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
+	/*
+	 * KVM_REQ_HV_TLB_FLUSH flushes entries from either L1's VPID or
+	 * L2's VPID 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 Direct 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);
+
 	/*
 	 * If vmcs12 doesn't use VPID, L1 expects linear and combined mappings
 	 * for *all* contexts to be flushed on VM-Enter/VM-Exit, i.e. it's a
@@ -5976,6 +5987,11 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu,
 		 * Handle L2's bus locks in L0 directly.
 		 */
 		return true;
+	case EXIT_REASON_VMCALL:
+		/* Hyper-V Direct TLB flush hypercall is handled by L0 */
+		return kvm_hv_direct_tlb_flush_exposed(vcpu) &&
+			nested_evmcs_direct_flush_enabled(vcpu) &&
+			kvm_hv_is_tlb_flush_hcall(vcpu);
 	default:
 		break;
 	}
-- 
2.35.1