KVM: nVMX: Drop redundant checks on vmcs12 in EPTP switching emulation

Drop the explicit check on EPTP switching being enabled.  The EPTP
switching check is handled in the generic VMFUNC function check, while
the underlying VMFUNC enablement check is done by hardware and redone
by generic VMFUNC emulation.

The vmcs12 EPT check is handled by KVM at VM-Enter in the form of a
consistency check, keep it but add a WARN.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210609234235.1244004-16-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -5506,10 +5506,8 @@ static int nested_vmx_eptp_switching(struct kvm_vcpu *vcpu,
 	u32 index = kvm_rcx_read(vcpu);
 	u64 new_eptp;
 
-	if (!nested_cpu_has_eptp_switching(vmcs12) ||
-	    !nested_cpu_has_ept(vmcs12))
+	if (WARN_ON_ONCE(!nested_cpu_has_ept(vmcs12)))
 		return 1;
-
 	if (index >= VMFUNC_EPTP_ENTRIES)
 		return 1;