From: Mihai Donțu <mdo...@bitdefender.com>

For now, this command returns only the number of online vCPUs.

The introspection tool uses the vCPU index to specify to which vCPU
the introspection command applies to.

Signed-off-by: Mihai Donțu <mdo...@bitdefender.com>
Signed-off-by: Adalbert Lazăr <ala...@bitdefender.com>
---
 Documentation/virt/kvm/kvmi.rst               | 18 ++++++++++
 include/uapi/linux/kvmi.h                     |  6 ++++
 .../testing/selftests/kvm/x86_64/kvmi_test.c  | 35 +++++++++++++++++--
 virt/kvm/introspection/kvmi_msg.c             | 13 +++++++
 4 files changed, 69 insertions(+), 3 deletions(-)

diff --git a/Documentation/virt/kvm/kvmi.rst b/Documentation/virt/kvm/kvmi.rst
index a2cda3268da0..a81f22cb8c18 100644
--- a/Documentation/virt/kvm/kvmi.rst
+++ b/Documentation/virt/kvm/kvmi.rst
@@ -323,3 +323,21 @@ This command is always allowed.
 * -KVM_ENOENT - the event specified by ``id`` is unsupported
 * -KVM_EPERM - the event specified by ``id`` is disallowed
 * -KVM_EINVAL - the padding is not zero
+
+4. KVMI_VM_GET_INFO
+-------------------
+
+:Architectures: all
+:Versions: >= 1
+:Parameters: none
+:Returns:
+
+::
+
+       struct kvmi_error_code;
+       struct kvmi_vm_get_info_reply {
+               __u32 vcpu_count;
+               __u32 padding[3];
+       };
+
+Returns the number of online vCPUs.
diff --git a/include/uapi/linux/kvmi.h b/include/uapi/linux/kvmi.h
index e55a0fa66ac5..eabaf7cea1df 100644
--- a/include/uapi/linux/kvmi.h
+++ b/include/uapi/linux/kvmi.h
@@ -17,6 +17,7 @@ enum {
        KVMI_GET_VERSION      = 1,
        KVMI_VM_CHECK_COMMAND = 2,
        KVMI_VM_CHECK_EVENT   = 3,
+       KVMI_VM_GET_INFO      = 4,
 
        KVMI_NUM_MESSAGES
 };
@@ -63,4 +64,9 @@ struct kvmi_vm_check_event {
        __u32 padding2;
 };
 
+struct kvmi_vm_get_info_reply {
+       __u32 vcpu_count;
+       __u32 padding[3];
+};
+
 #endif /* _UAPI__LINUX_KVMI_H */
diff --git a/tools/testing/selftests/kvm/x86_64/kvmi_test.c 
b/tools/testing/selftests/kvm/x86_64/kvmi_test.c
index 28216c4e8b9d..1f4a165ab640 100644
--- a/tools/testing/selftests/kvm/x86_64/kvmi_test.c
+++ b/tools/testing/selftests/kvm/x86_64/kvmi_test.c
@@ -84,6 +84,16 @@ static void set_command_perm(struct kvm_vm *vm, __s32 id, 
__u32 allow,
                 "KVM_INTROSPECTION_COMMAND");
 }
 
+static void disallow_command(struct kvm_vm *vm, __s32 id)
+{
+       set_command_perm(vm, id, 0, 0);
+}
+
+static void allow_command(struct kvm_vm *vm, __s32 id)
+{
+       set_command_perm(vm, id, 1, 0);
+}
+
 static void hook_introspection(struct kvm_vm *vm)
 {
        __u32 allow = 1, disallow = 0, allow_inval = 2;
@@ -258,14 +268,18 @@ static void cmd_vm_check_command(__u16 id, __u16 padding, 
int expected_err)
                -r, kvm_strerror(-r), expected_err);
 }
 
-static void test_cmd_vm_check_command(void)
+static void test_cmd_vm_check_command(struct kvm_vm *vm)
 {
-       __u16 valid_id = KVMI_GET_VERSION, invalid_id = 0xffff;
+       __u16 valid_id = KVMI_VM_GET_INFO, invalid_id = 0xffff;
        __u16 padding = 1, no_padding = 0;
 
        cmd_vm_check_command(valid_id, no_padding, 0);
        cmd_vm_check_command(valid_id, padding, -KVM_EINVAL);
        cmd_vm_check_command(invalid_id, no_padding, -KVM_ENOENT);
+
+       disallow_command(vm, valid_id);
+       cmd_vm_check_command(valid_id, no_padding, -KVM_EPERM);
+       allow_command(vm, valid_id);
 }
 
 static void cmd_vm_check_event(__u16 id, __u16 padding, int expected_err)
@@ -295,6 +309,20 @@ static void test_cmd_vm_check_event(void)
        cmd_vm_check_event(invalid_id, no_padding, -KVM_ENOENT);
 }
 
+static void test_cmd_vm_get_info(void)
+{
+       struct kvmi_vm_get_info_reply rpl;
+       struct kvmi_msg_hdr req;
+
+       test_vm_command(KVMI_VM_GET_INFO, &req, sizeof(req), &rpl,
+                       sizeof(rpl));
+       TEST_ASSERT(rpl.vcpu_count == 1,
+                   "Unexpected number of vCPU count %u\n",
+                   rpl.vcpu_count);
+
+       pr_info("vcpu count: %u\n", rpl.vcpu_count);
+}
+
 static void test_introspection(struct kvm_vm *vm)
 {
        setup_socket();
@@ -302,8 +330,9 @@ static void test_introspection(struct kvm_vm *vm)
 
        test_cmd_invalid();
        test_cmd_get_version();
-       test_cmd_vm_check_command();
+       test_cmd_vm_check_command(vm);
        test_cmd_vm_check_event();
+       test_cmd_vm_get_info();
 
        unhook_introspection(vm);
 }
diff --git a/virt/kvm/introspection/kvmi_msg.c 
b/virt/kvm/introspection/kvmi_msg.c
index 86c356afc154..3df18f7965c0 100644
--- a/virt/kvm/introspection/kvmi_msg.c
+++ b/virt/kvm/introspection/kvmi_msg.c
@@ -150,6 +150,18 @@ static int handle_vm_check_event(struct kvm_introspection 
*kvmi,
        return kvmi_msg_vm_reply(kvmi, msg, ec, NULL, 0);
 }
 
+static int handle_vm_get_info(struct kvm_introspection *kvmi,
+                             const struct kvmi_msg_hdr *msg,
+                             const void *req)
+{
+       struct kvmi_vm_get_info_reply rpl;
+
+       memset(&rpl, 0, sizeof(rpl));
+       rpl.vcpu_count = atomic_read(&kvmi->kvm->online_vcpus);
+
+       return kvmi_msg_vm_reply(kvmi, msg, 0, &rpl, sizeof(rpl));
+}
+
 /*
  * These commands are executed by the receiving thread.
  */
@@ -158,6 +170,7 @@ static int(*const msg_vm[])(struct kvm_introspection *,
        [KVMI_GET_VERSION]      = handle_get_version,
        [KVMI_VM_CHECK_COMMAND] = handle_vm_check_command,
        [KVMI_VM_CHECK_EVENT]   = handle_vm_check_event,
+       [KVMI_VM_GET_INFO]      = handle_vm_get_info,
 };
 
 static bool is_vm_command(u16 id)
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