KVM: nVMX: Ensure KVM_REQ_GET_NESTED_STATE_PAGES is cleared on VM-Exit

Always check and clear KVM_REQ_GET_NESTED_STATE_PAGES when emulating a
nested VM-Exit to ensure the request is cleared, even when KVM was built
with CONFIG_KVM_HYPERV=n, as KVM subtly relies on the "check" to clear
the flag and thus avoid double-mapping the vmcs12 pages, e.g. if KVM
manages to bail from VM-Enter without processing the request, and then
emulates VMLAUNCH or VMRESUME.

Fixes: b4f69df0f6 ("KVM: x86: Make Hyper-V emulation optional")
Cc: [email protected]
Reported-by: Yosry Ahmed <[email protected]>
Reviewed-by: Yosry Ahmed <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

arch/x86/kvm/vmx/nested.c

@@ -5081,8 +5081,9 @@ void __nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
 	/* trying to cancel vmlaunch/vmresume is a bug */
 	kvm_warn_on_nested_run_pending(vcpu);
 
-#ifdef CONFIG_KVM_HYPERV
+	/* Note, "checking" the request also clears the request. */
 	if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
+#ifdef CONFIG_KVM_HYPERV
 		/*
 		 * KVM_REQ_GET_NESTED_STATE_PAGES is also used to map
 		 * Enlightened VMCS after migration and we still need to
@@ -5090,8 +5091,8 @@ void __nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
 		 * the first L2 run.
 		 */
 		(void)nested_get_evmcs_page(vcpu);
-	}
 #endif
+	}
 
 	/* Service pending TLB flush requests for L2 before switching to L1. */
 	kvm_service_local_tlb_flush_requests(vcpu);