KVM: nVMX: Introduce 'EVMPTR_MAP_PENDING' post-migration state

Unlike regular set_current_vmptr(), nested_vmx_handle_enlightened_vmptrld()
can not be called directly from vmx_set_nested_state() as KVM may not have
all the information yet (e.g. HV_X64_MSR_VP_ASSIST_PAGE MSR may not be
restored yet). Enlightened VMCS is mapped later while getting nested state
pages. In the meantime, vmx->nested.hv_evmcs_vmptr remains 'EVMPTR_INVALID'
and it's indistinguishable from 'evmcs is not in use' case. This leads to
certain issues, in particular, if KVM_GET_NESTED_STATE is called right
after KVM_SET_NESTED_STATE, KVM_STATE_NESTED_EVMCS flag in the resulting
state will be unset (and such state will later fail to load).

Introduce 'EVMPTR_MAP_PENDING' state to detect not-yet-mapped eVMCS after
restore. With this, the 'is_guest_mode(vcpu)' hack in vmx_has_valid_vmcs12()
is no longer needed.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210526132026.270394-6-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/evmcs.h

@@ -198,10 +198,11 @@ static inline void evmcs_touch_msr_bitmap(void) {}
 #endif /* IS_ENABLED(CONFIG_HYPERV) */
 
 #define EVMPTR_INVALID (-1ULL)
+#define EVMPTR_MAP_PENDING (-2ULL)
 
 static inline bool evmptr_is_valid(u64 evmptr)
 {
-	return evmptr != EVMPTR_INVALID;
+	return evmptr != EVMPTR_INVALID && evmptr != EVMPTR_MAP_PENDING;
 }
 
 enum nested_evmptrld_status {

arch/x86/kvm/vmx/nested.c

@@ -3102,7 +3102,7 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
 	 * properly reflected.
 	 */
 	if (vmx->nested.enlightened_vmcs_enabled &&
-	    !evmptr_is_valid(vmx->nested.hv_evmcs_vmptr)) {
+	    vmx->nested.hv_evmcs_vmptr == EVMPTR_MAP_PENDING) {
 		enum nested_evmptrld_status evmptrld_status =
 			nested_vmx_handle_enlightened_vmptrld(vcpu, false);
 
@@ -6095,7 +6095,8 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
 		if (vmx_has_valid_vmcs12(vcpu)) {
 			kvm_state.size += sizeof(user_vmx_nested_state->vmcs12);
 
-			if (evmptr_is_valid(vmx->nested.hv_evmcs_vmptr))
+			/* 'hv_evmcs_vmptr' can also be EVMPTR_MAP_PENDING here */
+			if (vmx->nested.hv_evmcs_vmptr != EVMPTR_INVALID)
 				kvm_state.flags |= KVM_STATE_NESTED_EVMCS;
 
 			if (is_guest_mode(vcpu) &&
@@ -6294,6 +6295,7 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 		 * restored yet. EVMCS will be mapped from
 		 * nested_get_vmcs12_pages().
 		 */
+		vmx->nested.hv_evmcs_vmptr = EVMPTR_MAP_PENDING;
 		kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
 	} else {
 		return -EINVAL;

arch/x86/kvm/vmx/nested.h

@@ -56,14 +56,9 @@ static inline int vmx_has_valid_vmcs12(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
-	/*
-	 * In case we do two consecutive get/set_nested_state()s while L2 was
-	 * running hv_evmcs may end up not being mapped (we map it from
-	 * nested_vmx_run()/vmx_vcpu_run()). Check is_guest_mode() as we always
-	 * have vmcs12 if it is true.
-	 */
-	return is_guest_mode(vcpu) || vmx->nested.current_vmptr != -1ull ||
-		evmptr_is_valid(vmx->nested.hv_evmcs_vmptr);
+	/* 'hv_evmcs_vmptr' can also be EVMPTR_MAP_PENDING here */
+	return vmx->nested.current_vmptr != -1ull ||
+		vmx->nested.hv_evmcs_vmptr != EVMPTR_INVALID;
 }
 
 static inline u16 nested_get_vpid02(struct kvm_vcpu *vcpu)