KVM: selftests: Clean up requirements for XFD-aware XSAVE features

Provide informative error messages for the various checks related to
requesting access to XSAVE features that are buried behind XSAVE Feature
Disabling (XFD).

Opportunistically rename the helper to have "require" in the name so that
it's somewhat obvious that the helper may skip the test.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-41-seanjc@google.com

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

@@ -832,7 +832,10 @@ void vm_set_page_table_entry(struct kvm_vm *vm, struct kvm_vcpu *vcpu,
 uint64_t kvm_hypercall(uint64_t nr, uint64_t a0, uint64_t a1, uint64_t a2,
 		       uint64_t a3);
 
-void vm_xsave_req_perm(int bit);
+void __vm_xsave_require_permission(int bit, const char *name);
+
+#define vm_xsave_require_permission(perm)	\
+	__vm_xsave_require_permission(perm, #perm)
 
 enum pg_level {
 	PG_LEVEL_NONE,

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

@@ -578,7 +578,7 @@ static void vcpu_setup(struct kvm_vm *vm, struct kvm_vcpu *vcpu)
 	vcpu_sregs_set(vcpu, &sregs);
 }
 
-void vm_xsave_req_perm(int bit)
+void __vm_xsave_require_permission(int bit, const char *name)
 {
 	int kvm_fd;
 	u64 bitmask;
@@ -596,10 +596,12 @@ void vm_xsave_req_perm(int bit)
 	close(kvm_fd);
 
 	if (rc == -1 && (errno == ENXIO || errno == EINVAL))
-		exit(KSFT_SKIP);
+		__TEST_REQUIRE(0, "KVM_X86_XCOMP_GUEST_SUPP not supported");
+
 	TEST_ASSERT(rc == 0, "KVM_GET_DEVICE_ATTR(0, KVM_X86_XCOMP_GUEST_SUPP) error: %ld", rc);
 
-	TEST_REQUIRE(bitmask & (1ULL << bit));
+	__TEST_REQUIRE(bitmask & (1ULL << bit),
+		       "Required XSAVE feature '%s' not supported", name);
 
 	TEST_REQUIRE(!syscall(SYS_arch_prctl, ARCH_REQ_XCOMP_GUEST_PERM, bit));
 

tools/testing/selftests/kvm/x86_64/amx_test.c

@@ -307,7 +307,7 @@ int main(int argc, char *argv[])
 	u32 amx_offset;
 	int stage, ret;
 
-	vm_xsave_req_perm(XSTATE_XTILE_DATA_BIT);
+	vm_xsave_require_permission(XSTATE_XTILE_DATA_BIT);
 
 	/* Create VM */
 	vm = vm_create_with_one_vcpu(&vcpu, guest_code);