KVM: selftests: Test KVM_SET_CPUID2 after KVM_RUN

KVM forbids KVM_SET_CPUID2 after KVM_RUN was performed on a vCPU unless
the supplied CPUID data is equal to what was previously set. Test this.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220117150542.2176196-5-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

@@ -375,6 +375,8 @@ 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);
+int __vcpu_set_cpuid(struct kvm_vm *vm, uint32_t vcpuid,
+		     struct kvm_cpuid2 *cpuid);
 void vcpu_set_cpuid(struct kvm_vm *vm, uint32_t vcpuid,
 		    struct kvm_cpuid2 *cpuid);
 
@@ -418,6 +420,11 @@ uint64_t vm_get_page_table_entry(struct kvm_vm *vm, int vcpuid, uint64_t vaddr);
 void vm_set_page_table_entry(struct kvm_vm *vm, int vcpuid, uint64_t vaddr,
 			     uint64_t pte);
 
+/*
+ * get_cpuid() - find matching CPUID entry and return pointer to it.
+ */
+struct kvm_cpuid_entry2 *get_cpuid(struct kvm_cpuid2 *cpuid, uint32_t function,
+				   uint32_t index);
 /*
  * set_cpuid() - overwrites a matching cpuid entry with the provided value.
  *		 matches based on ent->function && ent->index. returns true

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

@@ -886,6 +886,17 @@ kvm_get_supported_cpuid_index(uint32_t function, uint32_t index)
 	return entry;
 }
 
+
+int __vcpu_set_cpuid(struct kvm_vm *vm, uint32_t vcpuid,
+		     struct kvm_cpuid2 *cpuid)
+{
+	struct vcpu *vcpu = vcpu_find(vm, vcpuid);
+
+	TEST_ASSERT(vcpu != NULL, "vcpu not found, vcpuid: %u", vcpuid);
+
+	return ioctl(vcpu->fd, KVM_SET_CPUID2, cpuid);
+}
+
 /*
  * VM VCPU CPUID Set
  *
@@ -903,12 +914,9 @@ kvm_get_supported_cpuid_index(uint32_t function, uint32_t index)
 void vcpu_set_cpuid(struct kvm_vm *vm,
 		uint32_t vcpuid, struct kvm_cpuid2 *cpuid)
 {
-	struct vcpu *vcpu = vcpu_find(vm, vcpuid);
 	int rc;
 
-	TEST_ASSERT(vcpu != NULL, "vcpu not found, vcpuid: %u", vcpuid);
-
-	rc = ioctl(vcpu->fd, KVM_SET_CPUID2, cpuid);
+	rc = __vcpu_set_cpuid(vm, vcpuid, cpuid);
 	TEST_ASSERT(rc == 0, "KVM_SET_CPUID2 failed, rc: %i errno: %i",
 		    rc, errno);
 
@@ -1384,6 +1392,23 @@ void assert_on_unhandled_exception(struct kvm_vm *vm, uint32_t vcpuid)
 	}
 }
 
+struct kvm_cpuid_entry2 *get_cpuid(struct kvm_cpuid2 *cpuid, uint32_t function,
+				   uint32_t index)
+{
+	int i;
+
+	for (i = 0; i < cpuid->nent; i++) {
+		struct kvm_cpuid_entry2 *cur = &cpuid->entries[i];
+
+		if (cur->function == function && cur->index == index)
+			return cur;
+	}
+
+	TEST_FAIL("CPUID function 0x%x index 0x%x not found ", function, index);
+
+	return NULL;
+}
+
 bool set_cpuid(struct kvm_cpuid2 *cpuid,
 	       struct kvm_cpuid_entry2 *ent)
 {

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

@@ -154,6 +154,34 @@ struct kvm_cpuid2 *vcpu_alloc_cpuid(struct kvm_vm *vm, vm_vaddr_t *p_gva, struct
 	return guest_cpuids;
 }
 
+static void set_cpuid_after_run(struct kvm_vm *vm, struct kvm_cpuid2 *cpuid)
+{
+	struct kvm_cpuid_entry2 *ent;
+	int rc;
+	u32 eax, ebx, x;
+
+	/* Setting unmodified CPUID is allowed */
+	rc = __vcpu_set_cpuid(vm, VCPU_ID, cpuid);
+	TEST_ASSERT(!rc, "Setting unmodified CPUID after KVM_RUN failed: %d", rc);
+
+	/* Changing CPU features is forbidden */
+	ent = get_cpuid(cpuid, 0x7, 0);
+	ebx = ent->ebx;
+	ent->ebx--;
+	rc = __vcpu_set_cpuid(vm, VCPU_ID, cpuid);
+	TEST_ASSERT(rc, "Changing CPU features should fail");
+	ent->ebx = ebx;
+
+	/* Changing MAXPHYADDR is forbidden */
+	ent = get_cpuid(cpuid, 0x80000008, 0);
+	eax = ent->eax;
+	x = eax & 0xff;
+	ent->eax = (eax & ~0xffu) | (x - 1);
+	rc = __vcpu_set_cpuid(vm, VCPU_ID, cpuid);
+	TEST_ASSERT(rc, "Changing MAXPHYADDR should fail");
+	ent->eax = eax;
+}
+
 int main(void)
 {
 	struct kvm_cpuid2 *supp_cpuid, *cpuid2;
@@ -175,5 +203,7 @@ int main(void)
 	for (stage = 0; stage < 3; stage++)
 		run_vcpu(vm, VCPU_ID, stage);
 
+	set_cpuid_after_run(vm, cpuid2);
+
 	kvm_vm_free(vm);
 }