KVM: selftests: Check KVM's supported CPUID, not host CPUID, for XFD

Use kvm_cpu_has() to check for XFD supported in vm_xsave_req_perm(),
simply checking host CPUID doesn't guarantee KVM supports AMX/XFD.

Opportunistically hoist the check above the bit check; if XFD isn't
supported, it's far better to get a "not supported at all" message, as
opposed to a "feature X isn't supported" message".
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-39-seanjc@google.com

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

@@ -117,6 +117,7 @@ struct kvm_x86_cpu_feature {
 #define	X86_FEATURE_XTILECFG		KVM_X86_CPU_FEATURE(0xD, 0, EAX, 17)
 #define	X86_FEATURE_XTILEDATA		KVM_X86_CPU_FEATURE(0xD, 0, EAX, 18)
 #define	X86_FEATURE_XSAVES		KVM_X86_CPU_FEATURE(0xD, 1, EAX, 3)
+#define	X86_FEATURE_XFD			KVM_X86_CPU_FEATURE(0xD, 1, EAX, 4)
 
 /*
  * Extended Leafs, a.k.a. AMD defined

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

@@ -578,21 +578,6 @@ static void vcpu_setup(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
 	vcpu_sregs_set(vcpu, &sregs);
 }
 
-#define CPUID_XFD_BIT (1 << 4)
-static bool is_xfd_supported(void)
-{
-	int eax, ebx, ecx, edx;
-	const int leaf = 0xd, subleaf = 0x1;
-
-	__asm__ __volatile__(
-		"cpuid"
-		: /* output */ "=a"(eax), "=b"(ebx),
-		  "=c"(ecx), "=d"(edx)
-		: /* input */ "0"(leaf), "2"(subleaf));
-
-	return !!(eax & CPUID_XFD_BIT);
-}
-
 void vm_xsave_req_perm(int bit)
 {
 	int kvm_fd;
@@ -604,6 +589,8 @@ void vm_xsave_req_perm(int bit)
 		.addr = (unsigned long) &bitmask
 	};
 
+	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_XFD));
+
 	kvm_fd = open_kvm_dev_path_or_exit();
 	rc = __kvm_ioctl(kvm_fd, KVM_GET_DEVICE_ATTR, &attr);
 	close(kvm_fd);
@@ -614,8 +601,6 @@ void vm_xsave_req_perm(int bit)
 
 	TEST_REQUIRE(bitmask & (1ULL << bit));
 
-	TEST_REQUIRE(is_xfd_supported());
-
 	rc = syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, bit);
 
 	/*