Re: [PATCH v3 2/5] machine/nitro-enclave: Add vhost-user-vsock device

[Daniel P . Berrangé]

On Sat, Aug 10, 2024 at 10:44:59PM +0600, Dorjoy Chowdhury wrote:
> AWS Nitro Enclaves have built-in vhost-vsock device support which
> enables applications in enclave VMs to communicate with the parent
> EC2 VM over vsock. The enclave VMs have dynamic CID while the parent
> always has CID 3. In QEMU, the vsock emulation for nitro enclave is
> added using vhost-user-vsock as opposed to vhost-vsock. vhost-vsock
> doesn't support sibling VM communication which is needed for nitro
> enclaves.
> 
> In QEMU's nitro-enclave emulation, for the vsock communication to CID
> 3 to work, another process that does the vsock emulation in  userspace
> must be run, for example, vhost-device-vsock[1] from rust-vmm, with
> necessary vsock communication support in another guest VM with CID 3.
> A new mandatory nitro-enclave machine option 'vsock' has been added.
> The value for this option should be the chardev id from the '-chardev'
> option for the vhost-user-vsock device to work.
> 
> Using vhost-user-vsock also enables the possibility to implement some
> proxying support in the vhost-user-vsock daemon that will forward all
> the packets to the host machine instead of CID 3 so that users of
> nitro-enclave can run the necessary applications in their host machine
> instead of running another whole VM with CID 3.
> 
> [1] https://github.com/rust-vmm/vhost-device/tree/main/vhost-device-vsock
> 
> Signed-off-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
> ---
>  backends/hostmem-memfd.c        |   2 -
>  hw/core/machine.c               |  71 +++++++++---------
>  hw/i386/Kconfig                 |   1 +
>  hw/i386/nitro_enclave.c         | 123 ++++++++++++++++++++++++++++++++
>  include/hw/boards.h             |   2 +
>  include/hw/i386/nitro_enclave.h |   8 +++
>  include/sysemu/hostmem.h        |   2 +
>  7 files changed, 174 insertions(+), 35 deletions(-)
> 

> diff --git a/hw/i386/nitro_enclave.c b/hw/i386/nitro_enclave.c
> index 98690c6373..280ab4cc9b 100644
> --- a/hw/i386/nitro_enclave.c
> +++ b/hw/i386/nitro_enclave.c
> @@ -11,11 +11,81 @@
>  #include "qemu/osdep.h"
>  #include "qemu/error-report.h"
>  #include "qapi/error.h"
> +#include "qom/object_interfaces.h"
>  
> +#include "chardev/char.h"
> +#include "hw/sysbus.h"
>  #include "hw/core/eif.h"
>  #include "hw/i386/x86.h"
>  #include "hw/i386/microvm.h"
>  #include "hw/i386/nitro_enclave.h"
> +#include "hw/virtio/virtio-mmio.h"
> +#include "hw/virtio/vhost-user-vsock.h"
> +#include "sysemu/hostmem.h"
> +
> +static BusState *find_free_virtio_mmio_bus(void)
> +{
> +    BusChild *kid;
> +    BusState *bus = sysbus_get_default();
> +
> +    QTAILQ_FOREACH(kid, &bus->children, sibling) {
> +        DeviceState *dev = kid->child;
> +        if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MMIO)) {
> +            VirtIOMMIOProxy *mmio = VIRTIO_MMIO(OBJECT(dev));
> +            VirtioBusState *mmio_virtio_bus = &mmio->bus;
> +            BusState *mmio_bus = &mmio_virtio_bus->parent_obj;
> +            if (QTAILQ_EMPTY(&mmio_bus->children)) {
> +                return mmio_bus;
> +            }
> +        }
> +    }
> +
> +    return NULL;
> +}
> +
> +static void vhost_user_vsock_init(NitroEnclaveMachineState *nems)
> +{
> +    DeviceState *dev = qdev_new(TYPE_VHOST_USER_VSOCK);
> +    VHostUserVSock *vsock = VHOST_USER_VSOCK(dev);
> +    BusState *bus;
> +
> +    if (!nems->vsock) {
> +        error_report("A valid chardev id for vhost-user-vsock device must be 
> "
> +                     "provided using the 'vsock' machine option");
> +        exit(1);
> +    }
> +
> +    bus = find_free_virtio_mmio_bus();
> +    if (!bus) {
> +        error_report("Failed to find bus for vhost-user-vsock device");
> +        exit(1);
> +    }
> +
> +    Chardev *chardev = qemu_chr_find(nems->vsock);
> +    if (!chardev) {
> +        error_report("Failed to find chardev with id %s", nems->vsock);
> +        exit(1);
> +    }
> +
> +    vsock->conf.chardev.chr = chardev;
> +
> +    qdev_realize_and_unref(dev, bus, &error_fatal);
> +}

Why does this machine need to create the vhost-user-vsock device itself ?
Doing it this way prevents the mgmt app from changing any of the other
vsock device settings beyond 'chardev'. The entity creating QEMU can use
-device to create the vsock device.


> +
> +static void nitro_enclave_devices_init(NitroEnclaveMachineState *nems)
> +{
> +    vhost_user_vsock_init(nems);
> +}
> +
> +static void nitro_enclave_machine_state_init(MachineState *machine)
> +{
> +    NitroEnclaveMachineClass *ne_class =
> +        NITRO_ENCLAVE_MACHINE_GET_CLASS(machine);
> +    NitroEnclaveMachineState *ne_state = NITRO_ENCLAVE_MACHINE(machine);
> +
> +    ne_class->parent_init(machine);
> +    nitro_enclave_devices_init(ne_state);
> +}
>  
>  static void nitro_enclave_machine_initfn(Object *obj)
>  {
> @@ -66,15 +136,68 @@ static void x86_load_eif(X86MachineState *x86ms, 
> FWCfgState *fw_cfg,
>      return;
>  }
>  
> +static bool create_memfd_backend(MachineState *ms, const char *path,
> +                                 Error **errp)
> +{
> +    Object *obj;
> +    MachineClass *mc = MACHINE_GET_CLASS(ms);
> +    bool r = false;
> +
> +    obj = object_new(TYPE_MEMORY_BACKEND_MEMFD);
> +    if (!object_property_set_int(obj, "size", ms->ram_size, errp)) {
> +        goto out;
> +    }
> +    object_property_add_child(object_get_objects_root(), mc->default_ram_id,
> +                              obj);
> +
> +    if (!user_creatable_complete(USER_CREATABLE(obj), errp)) {
> +        goto out;
> +    }
> +    r = object_property_set_link(OBJECT(ms), "memory-backend", obj, errp);
> +
> +out:
> +    object_unref(obj);
> +    return r;
> +}
> +
> +static char *nitro_enclave_get_vsock_chardev_id(Object *obj, Error **errp)
> +{
> +    NitroEnclaveMachineState *nems = NITRO_ENCLAVE_MACHINE(obj);
> +
> +    return g_strdup(nems->vsock);
> +}
> +
> +static void nitro_enclave_set_vsock_chardev_id(Object *obj, const char 
> *value,
> +                                               Error **errp)
> +{
> +    NitroEnclaveMachineState *nems = NITRO_ENCLAVE_MACHINE(obj);
> +
> +    g_free(nems->vsock);
> +    nems->vsock = g_strdup(value);
> +}
> +
>  static void nitro_enclave_class_init(ObjectClass *oc, void *data)
>  {
>      MachineClass *mc = MACHINE_CLASS(oc);
>      MicrovmMachineClass *mmc = MICROVM_MACHINE_CLASS(oc);
> +    NitroEnclaveMachineClass *nemc = NITRO_ENCLAVE_MACHINE_CLASS(oc);
>  
>      mmc->x86_load_linux = x86_load_eif;
>  
>      mc->family = "nitro_enclave_i386";
>      mc->desc = "AWS Nitro Enclave";
> +
> +    nemc->parent_init = mc->init;
> +    mc->init = nitro_enclave_machine_state_init;
> +
> +    mc->create_default_memdev = create_memfd_backend;
> +
> +    object_class_property_add_str(oc, NITRO_ENCLAVE_VSOCK_CHARDEV_ID,
> +                                  nitro_enclave_get_vsock_chardev_id,
> +                                  nitro_enclave_set_vsock_chardev_id);
> +    object_class_property_set_description(oc, NITRO_ENCLAVE_VSOCK_CHARDEV_ID,
> +                                          "Set chardev id for 
> vhost-user-vsock "
> +                                          "device");
>  }
>  
>  static const TypeInfo nitro_enclave_machine_info = {
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index 48ff6d8b93..c268e7f005 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -308,6 +308,8 @@ struct MachineClass {
>      int64_t (*get_default_cpu_node_id)(const MachineState *ms, int idx);
>      ram_addr_t (*fixup_ram_size)(ram_addr_t size);
>      uint64_t smbios_memory_device_size;
> +    bool (*create_default_memdev)(MachineState *ms, const char *path,
> +                                  Error **errp);
>  };
>  
>  /**
> diff --git a/include/hw/i386/nitro_enclave.h b/include/hw/i386/nitro_enclave.h
> index a1dada9371..3e302de851 100644
> --- a/include/hw/i386/nitro_enclave.h
> +++ b/include/hw/i386/nitro_enclave.h
> @@ -14,12 +14,20 @@
>  #include "hw/i386/microvm.h"
>  #include "qom/object.h"
>  
> +/* Machine type options */
> +#define NITRO_ENCLAVE_VSOCK_CHARDEV_ID "vsock"
> +
>  struct NitroEnclaveMachineClass {
>      MicrovmMachineClass parent;
> +
> +    void (*parent_init)(MachineState *state);
>  };
>  
>  struct NitroEnclaveMachineState {
>      MicrovmMachineState parent;
> +
> +    /* Machine type options */
> +    char *vsock;
>  };
>  
>  #define TYPE_NITRO_ENCLAVE_MACHINE MACHINE_TYPE_NAME("nitro-enclave")
> diff --git a/include/sysemu/hostmem.h b/include/sysemu/hostmem.h
> index de47ae59e4..67f45abe39 100644
> --- a/include/sysemu/hostmem.h
> +++ b/include/sysemu/hostmem.h
> @@ -39,6 +39,8 @@ OBJECT_DECLARE_TYPE(HostMemoryBackend, 
> HostMemoryBackendClass,
>   */
>  #define TYPE_MEMORY_BACKEND_FILE "memory-backend-file"
>  
> +#define TYPE_MEMORY_BACKEND_MEMFD "memory-backend-memfd"
> +
>  
>  /**
>   * HostMemoryBackendClass:
> -- 
> 2.39.2
> 

With regards,
Daniel
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