KVM: selftests: Check for KVM nEPT support using "feature" MSRs

When checking for nEPT support in KVM, use kvm_get_feature_msr() instead
of vcpu_get_msr() to retrieve KVM's default TRUE_PROCBASED_CTLS and
PROCBASED_CTLS2 MSR values, i.e. don't require a VM+vCPU to query nEPT
support.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20220927165209.930904-1-dmatlack@google.com
[sean: rebase on merged code, write changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/include/x86_64/vmx.h

@@ -572,7 +572,7 @@ void nested_map_memslot(struct vmx_pages *vmx, struct kvm_vm *vm,
 			uint32_t memslot);
 void nested_identity_map_1g(struct vmx_pages *vmx, struct kvm_vm *vm,
 			    uint64_t addr, uint64_t size);
-bool kvm_vm_has_ept(struct kvm_vm *vm);
+bool kvm_cpu_has_ept(void);
 void prepare_eptp(struct vmx_pages *vmx, struct kvm_vm *vm,
 		  uint32_t eptp_memslot);
 void prepare_virtualize_apic_accesses(struct vmx_pages *vmx, struct kvm_vm *vm);

tools/testing/selftests/kvm/lib/x86_64/vmx.c

@@ -544,26 +544,22 @@ void nested_identity_map_1g(struct vmx_pages *vmx, struct kvm_vm *vm,
 	__nested_map(vmx, vm, addr, addr, size, PG_LEVEL_1G);
 }
 
-bool kvm_vm_has_ept(struct kvm_vm *vm)
+bool kvm_cpu_has_ept(void)
 {
-	struct kvm_vcpu *vcpu;
 	uint64_t ctrl;
 
-	vcpu = list_first_entry(&vm->vcpus, struct kvm_vcpu, list);
-	TEST_ASSERT(vcpu, "Cannot determine EPT support without vCPUs.\n");
-
-	ctrl = vcpu_get_msr(vcpu, MSR_IA32_VMX_TRUE_PROCBASED_CTLS) >> 32;
+	ctrl = kvm_get_feature_msr(MSR_IA32_VMX_TRUE_PROCBASED_CTLS) >> 32;
 	if (!(ctrl & CPU_BASED_ACTIVATE_SECONDARY_CONTROLS))
 		return false;
 
-	ctrl = vcpu_get_msr(vcpu, MSR_IA32_VMX_PROCBASED_CTLS2) >> 32;
+	ctrl = kvm_get_feature_msr(MSR_IA32_VMX_PROCBASED_CTLS2) >> 32;
 	return ctrl & SECONDARY_EXEC_ENABLE_EPT;
 }
 
 void prepare_eptp(struct vmx_pages *vmx, struct kvm_vm *vm,
 		  uint32_t eptp_memslot)
 {
-	TEST_REQUIRE(kvm_vm_has_ept(vm));
+	TEST_REQUIRE(kvm_cpu_has_ept());
 
 	vmx->eptp = (void *)vm_vaddr_alloc_page(vm);
 	vmx->eptp_hva = addr_gva2hva(vm, (uintptr_t)vmx->eptp);