[PATCH v6 21/38] KVM: nVMX: hyper-v: Enable L2 TLB flush

[Vitaly Kuznetsov]

Enable L2 TLB flush feature on nVMX when:
- Enlightened VMCS is in use.
- The feature flag is enabled in eVMCS.
- The feature flag 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).

Note: nested_evmcs_l2_tlb_flush_enabled() uses cached VP assist page copy
which gets updated from nested_vmx_handle_enlightened_vmptrld(). This is
also guaranteed to happen post migration with eVMCS backed L2 running.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/evmcs.c  | 17 +++++++++++++++++
 arch/x86/kvm/vmx/evmcs.h  | 10 ++++++++++
 arch/x86/kvm/vmx/nested.c | 22 ++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
index 7cd7b16942c6..870de69172be 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"
@@ -433,6 +434,22 @@ int nested_enable_evmcs(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+bool nested_evmcs_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu)
+{
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct hv_enlightened_vmcs *evmcs = vmx->nested.hv_evmcs;
+
+	if (!hv_vcpu || !evmcs)
+		return false;
+
+	if (!evmcs->hv_enlightenments_control.nested_flush_hypercall)
+		return false;
+
+	return hv_vcpu->vp_assist_page.nested_control.features.directhypercall;
+}
+
 void vmx_hv_inject_synthetic_vmexit_post_tlb_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 22d238b36238..0267b6191e6c 100644
--- a/arch/x86/kvm/vmx/evmcs.h
+++ b/arch/x86/kvm/vmx/evmcs.h
@@ -66,6 +66,15 @@ 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)
 
+/*
+ * Note, Hyper-V isn't actually stealing bit 28 from Intel, just abusing it by
+ * pairing it with architecturally impossible exit reasons.  Bit 28 is set only
+ * on SMI exits to a SMI transfer monitor (STM) and if and only if a MTF VM-Exit
+ * is pending.  I.e. it will never be set by hardware for non-SMI exits (there
+ * are only three), nor will it ever be set unless the VMM is an STM.
+ */
+#define HV_VMX_SYNTHETIC_EXIT_REASON_TRAP_AFTER_FLUSH 0x10000031
+
 struct evmcs_field {
 	u16 offset;
 	u16 clean_field;
@@ -245,6 +254,7 @@ 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_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu);
 void vmx_hv_inject_synthetic_vmexit_post_tlb_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 87bff81f7f3e..69d06f77d7b4 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1170,6 +1170,17 @@ 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 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);
+
 	/*
 	 * 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
@@ -3278,6 +3289,12 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 
 static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)
 {
+	/*
+	 * Note: nested_get_evmcs_page() also updates 'vp_assist_page' copy
+	 * in 'struct kvm_vcpu_hv' in case eVMCS is in use, this is mandatory
+	 * to make nested_evmcs_l2_tlb_flush_enabled() work correctly post
+	 * migration.
+	 */
 	if (!nested_get_evmcs_page(vcpu)) {
 		pr_debug_ratelimited("%s: enlightened vmptrld failed\n",
 				     __func__);
@@ -6007,6 +6024,11 @@ 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 L2 TLB flush hypercall is handled by L0 */
+		return guest_hv_cpuid_has_l2_tlb_flush(vcpu) &&
+			nested_evmcs_l2_tlb_flush_enabled(vcpu) &&
+			kvm_hv_is_tlb_flush_hcall(vcpu);
 	default:
 		break;
 	}
-- 
2.35.3