KVM: selftests: Cache list of MSRs to save/restore

Cache the list of MSRs to save restore, mostly to justify not freeing the
list in the caller, which simplifies consumption of the list.

Opportunistically move the XSS test's so called is_supported_msr() to
common code as kvm_msr_is_in_save_restore_list().  The XSS is "supported"
by KVM, it's simply not in the save/restore list because KVM doesn't yet
allow a non-zero value.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

@@ -427,8 +427,10 @@ void vcpu_load_state(struct kvm_vm *vm, uint32_t vcpuid,
 		     struct kvm_x86_state *state);
 void kvm_x86_state_cleanup(struct kvm_x86_state *state);
 
-struct kvm_msr_list *kvm_get_msr_index_list(void);
+const struct kvm_msr_list *kvm_get_msr_index_list(void);
+bool kvm_msr_is_in_save_restore_list(uint32_t msr_index);
 uint64_t kvm_get_feature_msr(uint64_t msr_index);
+
 struct kvm_cpuid2 *kvm_get_supported_cpuid(void);
 struct kvm_cpuid2 *vcpu_get_cpuid(struct kvm_vm *vm, uint32_t vcpuid);
 

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

@@ -719,18 +719,6 @@ struct kvm_cpuid2 *kvm_get_supported_cpuid(void)
 	return cpuid;
 }
 
-/*
- * KVM Get MSR
- *
- * Input Args:
- *   msr_index - Index of MSR
- *
- * Output Args: None
- *
- * Return: On success, value of the MSR. On failure a TEST_ASSERT is produced.
- *
- * Get value of MSR for VCPU.
- */
 uint64_t kvm_get_feature_msr(uint64_t msr_index)
 {
 	struct {
@@ -903,38 +891,47 @@ void vcpu_dump(FILE *stream, struct kvm_vm *vm, uint32_t vcpuid, uint8_t indent)
 	sregs_dump(stream, &sregs, indent + 4);
 }
 
-static int kvm_get_num_msrs_fd(int kvm_fd)
+const struct kvm_msr_list *kvm_get_msr_index_list(void)
 {
+	static struct kvm_msr_list *list;
 	struct kvm_msr_list nmsrs;
-	int r;
+	int kvm_fd, r;
+
+	if (list)
+		return list;
+
+	kvm_fd = open_kvm_dev_path_or_exit();
 
 	nmsrs.nmsrs = 0;
 	r = __kvm_ioctl(kvm_fd, KVM_GET_MSR_INDEX_LIST, &nmsrs);
 	TEST_ASSERT(r == -1 && errno == E2BIG,
-		    "Unexpected result from KVM_GET_MSR_INDEX_LIST probe, r: %i", r);
+		    "Expected -E2BIG, got rc: %i errno: %i (%s)",
+		    r, errno, strerror(errno));
 
-	return nmsrs.nmsrs;
-}
+	list = malloc(sizeof(*list) + nmsrs.nmsrs * sizeof(list->indices[0]));
+	TEST_ASSERT(list, "-ENOMEM when allocating MSR index list");
+	list->nmsrs = nmsrs.nmsrs;
 
-static int kvm_get_num_msrs(struct kvm_vm *vm)
-{
-	return kvm_get_num_msrs_fd(vm->kvm_fd);
+	kvm_ioctl(kvm_fd, KVM_GET_MSR_INDEX_LIST, list);
+	close(kvm_fd);
+
+	TEST_ASSERT(list->nmsrs == nmsrs.nmsrs,
+		    "Number of save/restore MSRs changed, was %d, now %d",
+		    nmsrs.nmsrs, list->nmsrs);
+	return list;
 }
 
-struct kvm_msr_list *kvm_get_msr_index_list(void)
+bool kvm_msr_is_in_save_restore_list(uint32_t msr_index)
 {
-	struct kvm_msr_list *list;
-	int nmsrs, kvm_fd;
-
-	kvm_fd = open_kvm_dev_path_or_exit();
+	const struct kvm_msr_list *list = kvm_get_msr_index_list();
+	int i;
 
-	nmsrs = kvm_get_num_msrs_fd(kvm_fd);
-	list = malloc(sizeof(*list) + nmsrs * sizeof(list->indices[0]));
-	list->nmsrs = nmsrs;
-	kvm_ioctl(kvm_fd, KVM_GET_MSR_INDEX_LIST, list);
-	close(kvm_fd);
+	for (i = 0; i < list->nmsrs; ++i) {
+		if (list->indices[i] == msr_index)
+			return true;
+	}
 
-	return list;
+	return false;
 }
 
 static int vcpu_save_xsave_state(struct kvm_vm *vm, struct vcpu *vcpu,
@@ -955,10 +952,10 @@ static int vcpu_save_xsave_state(struct kvm_vm *vm, struct vcpu *vcpu,
 
 struct kvm_x86_state *vcpu_save_state(struct kvm_vm *vm, uint32_t vcpuid)
 {
+	const struct kvm_msr_list *msr_list = kvm_get_msr_index_list();
 	struct vcpu *vcpu = vcpu_get(vm, vcpuid);
-	struct kvm_msr_list *list;
 	struct kvm_x86_state *state;
-	int nmsrs, r, i;
+	int r, i;
 	static int nested_size = -1;
 
 	if (nested_size == -1) {
@@ -976,12 +973,7 @@ struct kvm_x86_state *vcpu_save_state(struct kvm_vm *vm, uint32_t vcpuid)
 	 */
 	vcpu_run_complete_io(vm, vcpuid);
 
-	nmsrs = kvm_get_num_msrs(vm);
-	list = malloc(sizeof(*list) + nmsrs * sizeof(list->indices[0]));
-	list->nmsrs = nmsrs;
-	kvm_ioctl(vm->kvm_fd, KVM_GET_MSR_INDEX_LIST, list);
-
-	state = malloc(sizeof(*state) + nmsrs * sizeof(state->msrs.entries[0]));
+	state = malloc(sizeof(*state) + msr_list->nmsrs * sizeof(state->msrs.entries[0]));
 	r = ioctl(vcpu->fd, KVM_GET_VCPU_EVENTS, &state->events);
 	TEST_ASSERT(r == 0, "Unexpected result from KVM_GET_VCPU_EVENTS, r: %i",
 		    r);
@@ -1019,18 +1011,17 @@ struct kvm_x86_state *vcpu_save_state(struct kvm_vm *vm, uint32_t vcpuid)
 	} else
 		state->nested.size = 0;
 
-	state->msrs.nmsrs = nmsrs;
-	for (i = 0; i < nmsrs; i++)
-		state->msrs.entries[i].index = list->indices[i];
+	state->msrs.nmsrs = msr_list->nmsrs;
+	for (i = 0; i < msr_list->nmsrs; i++)
+		state->msrs.entries[i].index = msr_list->indices[i];
 	r = ioctl(vcpu->fd, KVM_GET_MSRS, &state->msrs);
-	TEST_ASSERT(r == nmsrs, "Unexpected result from KVM_GET_MSRS, r: %i (failed MSR was 0x%x)",
-		    r, r == nmsrs ? -1 : list->indices[r]);
+	TEST_ASSERT(r == msr_list->nmsrs, "Unexpected result from KVM_GET_MSRS, r: %i (failed MSR was 0x%x)",
+		    r, r == msr_list->nmsrs ? -1 : msr_list->indices[r]);
 
 	r = ioctl(vcpu->fd, KVM_GET_DEBUGREGS, &state->debugregs);
 	TEST_ASSERT(r == 0, "Unexpected result from KVM_GET_DEBUGREGS, r: %i",
 		    r);
 
-	free(list);
 	return state;
 }
 

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

@@ -17,28 +17,11 @@
 
 #define X86_FEATURE_XSAVES	(1<<3)
 
-bool is_supported_msr(u32 msr_index)
-{
-	struct kvm_msr_list *list;
-	bool found = false;
-	int i;
-
-	list = kvm_get_msr_index_list();
-	for (i = 0; i < list->nmsrs; ++i) {
-		if (list->indices[i] == msr_index) {
-			found = true;
-			break;
-		}
-	}
-
-	free(list);
-	return found;
-}
-
 int main(int argc, char *argv[])
 {
 	struct kvm_cpuid_entry2 *entry;
 	bool xss_supported = false;
+	bool xss_in_msr_list;
 	struct kvm_vm *vm;
 	uint64_t xss_val;
 	int i, r;
@@ -64,12 +47,14 @@ int main(int argc, char *argv[])
 	 * At present, KVM only supports a guest IA32_XSS value of 0. Verify
 	 * that trying to set the guest IA32_XSS to an unsupported value fails.
 	 * Also, in the future when a non-zero value succeeds check that
-	 * IA32_XSS is in the KVM_GET_MSR_INDEX_LIST.
+	 * IA32_XSS is in the list of MSRs to save/restore.
 	 */
+	xss_in_msr_list = kvm_msr_is_in_save_restore_list(MSR_IA32_XSS);
 	for (i = 0; i < MSR_BITS; ++i) {
 		r = _vcpu_set_msr(vm, VCPU_ID, MSR_IA32_XSS, 1ull << i);
-		TEST_ASSERT(r == 0 || is_supported_msr(MSR_IA32_XSS),
-			    "IA32_XSS was able to be set, but was not found in KVM_GET_MSR_INDEX_LIST.\n");
+
+		TEST_ASSERT(r == 0 || xss_in_msr_list,
+			    "IA32_XSS was able to be set, but was not in save/restore list");
 	}
 
 	kvm_vm_free(vm);