On Tue, Nov 11, 2025 at 10:10:52AM +0100, Albert Esteve wrote:
> Add SHMEM_MAP/UNMAP requests to vhost-user for dynamic management of
> VIRTIO Shared Memory mappings.
>
> This implementation introduces VirtioSharedMemoryMapping as a unified
> QOM object that manages both the mapping metadata and MemoryRegion
> lifecycle. This object provides reference-counted lifecycle management
> with automatic cleanup of file descriptors and memory regions
> through QOM finalization.
>
> This request allows backends to dynamically map file descriptors into a
> VIRTIO Shared Memory Region identified by their shmid. Maps are created
> using memory_region_init_ram_from_fd() with configurable read/write
> permissions, and the resulting MemoryRegions are added as subregions to
> the shmem container region. The mapped memory is then advertised to the
> guest VIRTIO drivers as a base address plus offset for reading and
> writting according to the requested mmap flags.
>
> The backend can unmap memory ranges within a given VIRTIO Shared Memory
> Region to free resources. Upon receiving this message, the frontend
> removes the MemoryRegion as a subregion and automatically unreferences
> the VirtioSharedMemoryMapping object, triggering cleanup if no other
> references exist.
>
> Error handling has been improved to ensure consistent behavior across
> handlers that manage their own vhost_user_send_resp() calls. Since
> these handlers clear the VHOST_USER_NEED_REPLY_MASK flag, explicit
> error checking ensures proper connection closure on failures,
> maintaining the expected error flow.
>
> Note the memory region commit for these operations needs to be delayed
> until after we reply to the backend to avoid deadlocks. Otherwise,
> the MemoryListener would send a VHOST_USER_SET_MEM_TABLE message
> before the reply.
>
> Reviewed-by: Stefan Hajnoczi <[email protected]>
> Signed-off-by: Albert Esteve <[email protected]>
> ---
> hw/virtio/vhost-user.c | 269 ++++++++++++++++++++++
> hw/virtio/virtio.c | 199 ++++++++++++++++
> include/hw/virtio/virtio.h | 135 +++++++++++
> subprojects/libvhost-user/libvhost-user.c | 70 ++++++
> subprojects/libvhost-user/libvhost-user.h | 54 +++++
> 5 files changed, 727 insertions(+)
>
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 63fa9a1b4b..5706a2bd8a 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -104,6 +104,7 @@ typedef enum VhostUserRequest {
> VHOST_USER_GET_SHARED_OBJECT = 41,
> VHOST_USER_SET_DEVICE_STATE_FD = 42,
> VHOST_USER_CHECK_DEVICE_STATE = 43,
> + VHOST_USER_GET_SHMEM_CONFIG = 44,
> VHOST_USER_MAX
> } VhostUserRequest;
>
> @@ -115,6 +116,8 @@ typedef enum VhostUserBackendRequest {
> VHOST_USER_BACKEND_SHARED_OBJECT_ADD = 6,
> VHOST_USER_BACKEND_SHARED_OBJECT_REMOVE = 7,
> VHOST_USER_BACKEND_SHARED_OBJECT_LOOKUP = 8,
> + VHOST_USER_BACKEND_SHMEM_MAP = 9,
> + VHOST_USER_BACKEND_SHMEM_UNMAP = 10,
> VHOST_USER_BACKEND_MAX
> } VhostUserBackendRequest;
>
> @@ -136,6 +139,12 @@ typedef struct VhostUserMemRegMsg {
> VhostUserMemoryRegion region;
> } VhostUserMemRegMsg;
>
> +typedef struct VhostUserShMemConfig {
> + uint32_t nregions;
> + uint32_t padding;
> + uint64_t memory_sizes[VIRTIO_MAX_SHMEM_REGIONS];
> +} VhostUserShMemConfig;
> +
> typedef struct VhostUserLog {
> uint64_t mmap_size;
> uint64_t mmap_offset;
> @@ -192,6 +201,23 @@ typedef struct VhostUserShared {
> unsigned char uuid[16];
> } VhostUserShared;
>
> +/* For the flags field of VhostUserMMap */
> +#define VHOST_USER_FLAG_MAP_RW (1u << 0)
> +
> +typedef struct {
> + /* VIRTIO Shared Memory Region ID */
> + uint8_t shmid;
> + uint8_t padding[7];
> + /* File offset */
> + uint64_t fd_offset;
> + /* Offset within the VIRTIO Shared Memory Region */
> + uint64_t shm_offset;
> + /* Size of the mapping */
> + uint64_t len;
> + /* Flags for the mmap operation, from VHOST_USER_FLAG_MAP_* */
> + uint64_t flags;
> +} VhostUserMMap;
> +
> typedef struct {
> VhostUserRequest request;
>
> @@ -224,6 +250,8 @@ typedef union {
> VhostUserInflight inflight;
> VhostUserShared object;
> VhostUserTransferDeviceState transfer_state;
> + VhostUserMMap mmap;
> + VhostUserShMemConfig shmem;
> } VhostUserPayload;
>
> typedef struct VhostUserMsg {
> @@ -1771,6 +1799,196 @@ vhost_user_backend_handle_shared_object_lookup(struct
> vhost_user *u,
> return 0;
> }
>
> +/**
> + * vhost_user_backend_handle_shmem_map() - Handle SHMEM_MAP backend request
> + * @dev: vhost device
> + * @ioc: QIOChannel for communication
> + * @hdr: vhost-user message header
> + * @payload: message payload containing mapping details
> + * @fd: file descriptor for the shared memory region
> + *
> + * Handles VHOST_USER_BACKEND_SHMEM_MAP requests from the backend. Creates
> + * a VhostUserShmemObject to manage the shared memory mapping and adds it
> + * to the appropriate VirtIO shared memory region. The VhostUserShmemObject
> + * serves as an intermediate parent for the MemoryRegion, ensuring proper
> + * lifecycle management with reference counting.
> + *
> + * Returns: 0 on success, negative errno on failure
> + */
> +static int
> +vhost_user_backend_handle_shmem_map(struct vhost_dev *dev,
> + QIOChannel *ioc,
> + VhostUserHeader *hdr,
> + VhostUserPayload *payload,
> + int fd)
> +{
> + VirtioSharedMemory *shmem;
> + VhostUserMMap *vu_mmap = &payload->mmap;
> + VirtioSharedMemoryMapping *existing;
> + Error *local_err = NULL;
> + int ret = 0;
> +
> + if (fd < 0) {
> + error_report("Bad fd for map");
> + ret = -EBADF;
> + goto send_reply;
> + }
> +
> + if (QSIMPLEQ_EMPTY(&dev->vdev->shmem_list)) {
> + error_report("Device has no VIRTIO Shared Memory Regions. "
> + "Requested ID: %d", vu_mmap->shmid);
> + ret = -EFAULT;
> + goto send_reply;
> + }
> +
> + shmem = virtio_find_shmem_region(dev->vdev, vu_mmap->shmid);
> + if (!shmem) {
> + error_report("VIRTIO Shared Memory Region at "
> + "ID %d not found or uninitialized", vu_mmap->shmid);
> + ret = -EFAULT;
> + goto send_reply;
> + }
> +
> + if ((vu_mmap->shm_offset + vu_mmap->len) < vu_mmap->len ||
> + (vu_mmap->shm_offset + vu_mmap->len) > shmem->mr.size) {
> + error_report("Bad offset/len for mmap %" PRIx64 "+%" PRIx64,
> + vu_mmap->shm_offset, vu_mmap->len);
> + ret = -EFAULT;
> + goto send_reply;
> + }
> +
> + QTAILQ_FOREACH(existing, &shmem->mmaps, link) {
> + if (ranges_overlap(existing->offset, existing->len,
> + vu_mmap->shm_offset, vu_mmap->len)) {
> + error_report("VIRTIO Shared Memory mapping overlap");
> + ret = -EFAULT;
> + goto send_reply;
> + }
> + }
> +
> + memory_region_transaction_begin();
> +
> + /* Create VirtioSharedMemoryMapping object */
> + VirtioSharedMemoryMapping *mapping = virtio_shared_memory_mapping_new(
> + vu_mmap->shmid, fd, vu_mmap->fd_offset, vu_mmap->shm_offset,
> + vu_mmap->len, vu_mmap->flags & VHOST_USER_FLAG_MAP_RW);
> +
> + if (!mapping) {
> + ret = -EFAULT;
> + goto send_reply_commit;
> + }
> +
> + /* Add the mapping to the shared memory region */
> + if (virtio_add_shmem_map(shmem, mapping) != 0) {
> + error_report("Failed to add shared memory mapping");
> + object_unref(OBJECT(mapping));
> + ret = -EFAULT;
> + goto send_reply_commit;
> + }
> +
> +send_reply_commit:
> + /* Send reply and commit after transaction started */
> + if (hdr->flags & VHOST_USER_NEED_REPLY_MASK) {
> + payload->u64 = !!ret;
> + hdr->size = sizeof(payload->u64);
> + if (!vhost_user_send_resp(ioc, hdr, payload, &local_err)) {
> + error_report_err(local_err);
> + memory_region_transaction_commit();
> + return -EFAULT;
> + }
> + }
> + memory_region_transaction_commit();
> + return 0;
> +
> +send_reply:
> + if (hdr->flags & VHOST_USER_NEED_REPLY_MASK) {
> + payload->u64 = !!ret;
> + hdr->size = sizeof(payload->u64);
> + if (!vhost_user_send_resp(ioc, hdr, payload, &local_err)) {
> + error_report_err(local_err);
> + return -EFAULT;
> + }
> + }
> + return 0;
> +}
> +
> +/**
> + * vhost_user_backend_handle_shmem_unmap() - Handle SHMEM_UNMAP backend
> request
> + * @dev: vhost device
> + * @ioc: QIOChannel for communication
> + * @hdr: vhost-user message header
> + * @payload: message payload containing unmapping details
> + *
> + * Handles VHOST_USER_BACKEND_SHMEM_UNMAP requests from the backend. Removes
> + * the specified memory mapping from the VirtIO shared memory region. This
> + * automatically unreferences the associated VhostUserShmemObject, which may
> + * trigger its finalization and cleanup (munmap, close fd) if no other
> + * references exist.
> + *
> + * Returns: 0 on success, negative errno on failure
> + */
> +static int
> +vhost_user_backend_handle_shmem_unmap(struct vhost_dev *dev,
> + QIOChannel *ioc,
> + VhostUserHeader *hdr,
> + VhostUserPayload *payload)
> +{
> + VirtioSharedMemory *shmem;
shmem uninitialized here
> + VirtioSharedMemoryMapping *mmap = NULL;
but mmap is NULL here
> + VhostUserMMap *vu_mmap = &payload->mmap;
> + Error *local_err = NULL;
> + int ret = 0;
> +
> + if (QSIMPLEQ_EMPTY(&dev->vdev->shmem_list)) {
> + error_report("Device has no VIRTIO Shared Memory Regions. "
> + "Requested ID: %d", vu_mmap->shmid);
> + ret = -EFAULT;
> + goto send_reply;
> + }
> +
> + shmem = virtio_find_shmem_region(dev->vdev, vu_mmap->shmid);
initialized here
> + if (!shmem) {
> + error_report("VIRTIO Shared Memory Region at "
> + "ID %d not found or uninitialized", vu_mmap->shmid);
> + ret = -EFAULT;
> + goto send_reply;
> + }
> +
> + if ((vu_mmap->shm_offset + vu_mmap->len) < vu_mmap->len ||
> + (vu_mmap->shm_offset + vu_mmap->len) > shmem->mr.size) {
> + error_report("Bad offset/len for unmmap %" PRIx64 "+%" PRIx64,
> + vu_mmap->shm_offset, vu_mmap->len);
> + ret = -EFAULT;
> + goto send_reply;
> + }
> +
> + mmap = virtio_find_shmem_map(shmem, vu_mmap->shm_offset, vu_mmap->len);
before mmap
> + if (!mmap) {
> + error_report("Shared memory mapping not found at offset %" PRIx64
> + " with length %" PRIx64,
> + vu_mmap->shm_offset, vu_mmap->len);
> + ret = -EFAULT;
> + goto send_reply;
> + }
> +
> +send_reply:
> + if (hdr->flags & VHOST_USER_NEED_REPLY_MASK) {
> + payload->u64 = !!ret;
> + hdr->size = sizeof(payload->u64);
> + if (!vhost_user_send_resp(ioc, hdr, payload, &local_err)) {
> + error_report_err(local_err);
> + return -EFAULT;
> + }
> + }
> +
> + if (!ret && mmap) {
so there is no path on which mmap is !null but shmem is uninitialized
> + /* Free the MemoryRegion only after reply */
> + virtio_del_shmem_map(shmem, vu_mmap->shm_offset, vu_mmap->len);
however gcc is not clever enough to know it:
https://gitlab.com/mstredhat/qemu/-/jobs/12974202646
> + }
> +
> + return 0;
> +}
> +
> static void close_backend_channel(struct vhost_user *u)
> {
> g_source_destroy(u->backend_src);
> @@ -1844,6 +2062,21 @@ static gboolean backend_read(QIOChannel *ioc,
> GIOCondition condition,
> ret = vhost_user_backend_handle_shared_object_lookup(dev->opaque,
>
> &payload.object);
> break;
> + case VHOST_USER_BACKEND_SHMEM_MAP:
> + /* Handler manages its own response, check error and close
> connection */
> + reply_ack = false;
> + if (vhost_user_backend_handle_shmem_map(dev, ioc, &hdr, &payload,
> + fd ? fd[0] : -1) < 0) {
> + goto err;
> + }
> + break;
> + case VHOST_USER_BACKEND_SHMEM_UNMAP:
> + /* Handler manages its own response, check error and close
> connection */
> + reply_ack = false;
> + if (vhost_user_backend_handle_shmem_unmap(dev, ioc, &hdr, &payload)
> < 0) {
> + goto err;
> + }
> + break;
> default:
> error_report("Received unexpected msg type: %d.", hdr.request);
> ret = -EINVAL;
> @@ -3021,6 +3254,41 @@ static int vhost_user_check_device_state(struct
> vhost_dev *dev, Error **errp)
> return 0;
> }
>
> +static int vhost_user_get_shmem_config(struct vhost_dev *dev,
> + int *nregions,
> + uint64_t *memory_sizes,
> + Error **errp)
> +{
> + int ret;
> + VhostUserMsg msg = {
> + .hdr.request = VHOST_USER_GET_SHMEM_CONFIG,
> + .hdr.flags = VHOST_USER_VERSION,
> + };
> +
> + if (!virtio_has_feature(dev->protocol_features,
> + VHOST_USER_PROTOCOL_F_SHMEM)) {
> + *nregions = 0;
> + return 0;
> + }
> +
> + ret = vhost_user_write(dev, &msg, NULL, 0);
> + if (ret < 0) {
> + return ret;
> + }
> +
> + ret = vhost_user_read(dev, &msg);
> + if (ret < 0) {
> + return ret;
> + }
> +
> + assert(msg.payload.shmem.nregions <= VIRTIO_MAX_SHMEM_REGIONS);
> + *nregions = msg.payload.shmem.nregions;
> + memcpy(memory_sizes,
> + &msg.payload.shmem.memory_sizes,
> + sizeof(uint64_t) * VIRTIO_MAX_SHMEM_REGIONS);
> + return 0;
> +}
> +
> const VhostOps user_ops = {
> .backend_type = VHOST_BACKEND_TYPE_USER,
> .vhost_backend_init = vhost_user_backend_init,
> @@ -3059,4 +3327,5 @@ const VhostOps user_ops = {
> .vhost_supports_device_state = vhost_user_supports_device_state,
> .vhost_set_device_state_fd = vhost_user_set_device_state_fd,
> .vhost_check_device_state = vhost_user_check_device_state,
> + .vhost_get_shmem_config = vhost_user_get_shmem_config,
> };
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 257cda506a..33186f1977 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -3090,6 +3090,173 @@ int virtio_save(VirtIODevice *vdev, QEMUFile *f)
> return ret;
> }
>
> +VirtioSharedMemory *virtio_new_shmem_region(VirtIODevice *vdev, uint8_t
> shmid, uint64_t size)
> +{
> + VirtioSharedMemory *elem;
> + g_autofree char *name = NULL;
> +
> + elem = g_new0(VirtioSharedMemory, 1);
> + elem->shmid = shmid;
> +
> + /* Initialize embedded MemoryRegion as container for shmem mappings */
> + name = g_strdup_printf("virtio-shmem-%d", shmid);
> + memory_region_init(&elem->mr, OBJECT(vdev), name, size);
> + QTAILQ_INIT(&elem->mmaps);
> + QSIMPLEQ_INSERT_TAIL(&vdev->shmem_list, elem, entry);
> + return elem;
> +}
> +
> +VirtioSharedMemory *virtio_find_shmem_region(VirtIODevice *vdev, uint8_t
> shmid)
> +{
> + VirtioSharedMemory *shmem, *next;
> + QSIMPLEQ_FOREACH_SAFE(shmem, &vdev->shmem_list, entry, next) {
> + if (shmem->shmid == shmid) {
> + return shmem;
> + }
> + }
> + return NULL;
> +}
> +
> +static void virtio_shared_memory_mapping_instance_init(Object *obj)
> +{
> + VirtioSharedMemoryMapping *mapping = VIRTIO_SHARED_MEMORY_MAPPING(obj);
> +
> + mapping->shmid = 0;
> + mapping->offset = 0;
> + mapping->len = 0;
> + mapping->mr = NULL;
> +}
> +
> +static void virtio_shared_memory_mapping_instance_finalize(Object *obj)
> +{
> + VirtioSharedMemoryMapping *mapping = VIRTIO_SHARED_MEMORY_MAPPING(obj);
> +
> + /* Clean up MemoryRegion if it exists */
> + if (mapping->mr) {
> + /* Unparent the MemoryRegion to trigger cleanup */
> + object_unparent(OBJECT(mapping->mr));
> + mapping->mr = NULL;
> + }
> +}
> +
> +VirtioSharedMemoryMapping *virtio_shared_memory_mapping_new(uint8_t shmid,
> + int fd,
> + uint64_t
> fd_offset,
> + uint64_t
> shm_offset,
> + uint64_t len,
> + bool allow_write)
> +{
> + VirtioSharedMemoryMapping *mapping;
> + MemoryRegion *mr;
> + g_autoptr(GString) mr_name = g_string_new(NULL);
> + uint32_t ram_flags;
> + Error *local_err = NULL;
> +
> + if (len == 0) {
> + error_report("Shared memory mapping size cannot be zero");
> + return NULL;
> + }
> +
> + fd = dup(fd);
> + if (fd < 0) {
> + error_report("Failed to duplicate fd: %s", strerror(errno));
> + return NULL;
> + }
> +
> + /* Determine RAM flags */
> + ram_flags = RAM_SHARED;
> + if (!allow_write) {
> + ram_flags |= RAM_READONLY_FD;
> + }
> +
> + /* Create the VirtioSharedMemoryMapping */
> + mapping = VIRTIO_SHARED_MEMORY_MAPPING(
> + object_new(TYPE_VIRTIO_SHARED_MEMORY_MAPPING));
> +
> + /* Set up object properties */
> + mapping->shmid = shmid;
> + mapping->offset = shm_offset;
> + mapping->len = len;
> +
> + /* Create MemoryRegion as a child of this object */
> + mr = g_new0(MemoryRegion, 1);
> + g_string_printf(mr_name, "virtio-shmem-%d-%" PRIx64, shmid, shm_offset);
> +
> + /* Initialize MemoryRegion with file descriptor */
> + if (!memory_region_init_ram_from_fd(mr, OBJECT(mapping), mr_name->str,
> + len, ram_flags, fd, fd_offset,
> + &local_err)) {
> + error_report_err(local_err);
> + g_free(mr);
> + close(fd);
> + object_unref(OBJECT(mapping));
> + return NULL;
> + }
> +
> + mapping->mr = mr;
> + return mapping;
> +}
> +
> +int virtio_add_shmem_map(VirtioSharedMemory *shmem,
> + VirtioSharedMemoryMapping *mapping)
> +{
> + if (!mapping) {
> + error_report("VirtioSharedMemoryMapping cannot be NULL");
> + return -1;
> + }
> + if (!mapping->mr) {
> + error_report("VirtioSharedMemoryMapping has no MemoryRegion");
> + return -1;
> + }
> +
> + /* Validate boundaries against the VIRTIO shared memory region */
> + if (mapping->offset + mapping->len > shmem->mr.size) {
> + error_report("Memory exceeds the shared memory boundaries");
> + return -1;
> + }
> +
> + /* Add as subregion to the VIRTIO shared memory */
> + memory_region_add_subregion(&shmem->mr, mapping->offset, mapping->mr);
> +
> + /* Add to the mapped regions list */
> + QTAILQ_INSERT_TAIL(&shmem->mmaps, mapping, link);
> +
> + return 0;
> +}
> +
> +VirtioSharedMemoryMapping *virtio_find_shmem_map(VirtioSharedMemory *shmem,
> + hwaddr offset, uint64_t size)
> +{
> + VirtioSharedMemoryMapping *mapping;
> + QTAILQ_FOREACH(mapping, &shmem->mmaps, link) {
> + if (mapping->offset == offset && mapping->mr->size == size) {
> + return mapping;
> + }
> + }
> + return NULL;
> +}
> +
> +void virtio_del_shmem_map(VirtioSharedMemory *shmem, hwaddr offset,
> + uint64_t size)
> +{
> + VirtioSharedMemoryMapping *mapping = virtio_find_shmem_map(shmem,
> offset, size);
> + if (mapping == NULL) {
> + return;
> + }
> +
> + /*
> + * Remove from memory region first
> + */
> + memory_region_del_subregion(&shmem->mr, mapping->mr);
> +
> + /*
> + * Remove from list and unref the mapping which will trigger automatic
> cleanup
> + * when the reference count reaches zero.
> + */
> + QTAILQ_REMOVE(&shmem->mmaps, mapping, link);
> + object_unref(OBJECT(mapping));
> +}
> +
> /* A wrapper for use as a VMState .put function */
> static int virtio_device_put(QEMUFile *f, void *opaque, size_t size,
> const VMStateField *field, JSONWriter *vmdesc)
> @@ -3216,6 +3383,7 @@ void virtio_reset(void *opaque)
> {
> VirtIODevice *vdev = opaque;
> VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
> + VirtioSharedMemory *shmem;
> uint64_t features[VIRTIO_FEATURES_NU64S];
> int i;
>
> @@ -3255,6 +3423,14 @@ void virtio_reset(void *opaque)
> for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
> __virtio_queue_reset(vdev, i);
> }
> +
> + /* Mappings are removed to prevent stale fds from remaining open. */
> + QSIMPLEQ_FOREACH(shmem, &vdev->shmem_list, entry) {
> + while (!QTAILQ_EMPTY(&shmem->mmaps)) {
> + VirtioSharedMemoryMapping *mapping = QTAILQ_FIRST(&shmem->mmaps);
> + virtio_del_shmem_map(shmem, mapping->offset, mapping->mr->size);
> + }
> + }
> }
>
> static void virtio_device_check_notification_compatibility(VirtIODevice
> *vdev,
> @@ -3578,6 +3754,7 @@ void virtio_init(VirtIODevice *vdev, uint16_t
> device_id, size_t config_size)
> NULL, virtio_vmstate_change, vdev);
> vdev->device_endian = virtio_default_endian();
> vdev->use_guest_notifier_mask = true;
> + QSIMPLEQ_INIT(&vdev->shmem_list);
> }
>
> /*
> @@ -4089,11 +4266,24 @@ static void
> virtio_device_free_virtqueues(VirtIODevice *vdev)
> static void virtio_device_instance_finalize(Object *obj)
> {
> VirtIODevice *vdev = VIRTIO_DEVICE(obj);
> + VirtioSharedMemory *shmem;
>
> virtio_device_free_virtqueues(vdev);
>
> g_free(vdev->config);
> g_free(vdev->vector_queues);
> + while (!QSIMPLEQ_EMPTY(&vdev->shmem_list)) {
> + shmem = QSIMPLEQ_FIRST(&vdev->shmem_list);
> + while (!QTAILQ_EMPTY(&shmem->mmaps)) {
> + VirtioSharedMemoryMapping *mapping = QTAILQ_FIRST(&shmem->mmaps);
> + virtio_del_shmem_map(shmem, mapping->offset, mapping->mr->size);
> + }
> +
> + /* Clean up the embedded MemoryRegion */
> + object_unparent(OBJECT(&shmem->mr));
> + QSIMPLEQ_REMOVE_HEAD(&vdev->shmem_list, entry);
> + g_free(shmem);
> + }
> }
>
> static const Property virtio_properties[] = {
> @@ -4459,9 +4649,18 @@ static const TypeInfo virtio_device_info = {
> .class_size = sizeof(VirtioDeviceClass),
> };
>
> +static const TypeInfo virtio_shared_memory_mapping_info = {
> + .name = TYPE_VIRTIO_SHARED_MEMORY_MAPPING,
> + .parent = TYPE_OBJECT,
> + .instance_size = sizeof(VirtioSharedMemoryMapping),
> + .instance_init = virtio_shared_memory_mapping_instance_init,
> + .instance_finalize = virtio_shared_memory_mapping_instance_finalize,
> +};
> +
> static void virtio_register_types(void)
> {
> type_register_static(&virtio_device_info);
> + type_register_static(&virtio_shared_memory_mapping_info);
> }
>
> type_init(virtio_register_types)
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index d97529c3f1..3f6dfba321 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -99,6 +99,45 @@ enum virtio_device_endian {
> VIRTIO_DEVICE_ENDIAN_BIG,
> };
>
> +#define TYPE_VIRTIO_SHARED_MEMORY_MAPPING "virtio-shared-memory-mapping"
> +OBJECT_DECLARE_SIMPLE_TYPE(VirtioSharedMemoryMapping,
> VIRTIO_SHARED_MEMORY_MAPPING)
> +
> +/**
> + * VirtioSharedMemoryMapping:
> + * @parent: Parent QOM object
> + * @shmid: VIRTIO Shared Memory Region ID
> + * @fd: File descriptor for the shared memory region
> + * @offset: Offset within the VIRTIO Shared Memory Region
> + * @len: Size of the mapping
> + * @mr: MemoryRegion associated with this shared memory mapping
> + * @link: List entry for the shared memory region's mapping list
> + *
> + * A QOM object that represents an individual file descriptor-based shared
> + * memory mapping within a VIRTIO Shared Memory Region. It manages the
> + * MemoryRegion lifecycle and file descriptor cleanup through QOM reference
> + * counting. When the object is unreferenced and its reference count drops
> + * to zero, it automatically cleans up the MemoryRegion and closes the file
> + * descriptor.
> + */
> +struct VirtioSharedMemoryMapping {
> + Object parent;
> +
> + uint8_t shmid;
> + hwaddr offset;
> + uint64_t len;
> + MemoryRegion *mr;
> + QTAILQ_ENTRY(VirtioSharedMemoryMapping) link;
> +};
> +
> +struct VirtioSharedMemory {
> + uint8_t shmid;
> + MemoryRegion mr;
> + QTAILQ_HEAD(, VirtioSharedMemoryMapping) mmaps;
> + QSIMPLEQ_ENTRY(VirtioSharedMemory) entry;
> +};
> +
> +typedef struct VirtioSharedMemory VirtioSharedMemory;
> +
> /**
> * struct VirtIODevice - common VirtIO structure
> * @name: name of the device
> @@ -168,6 +207,8 @@ struct VirtIODevice
> */
> EventNotifier config_notifier;
> bool device_iotlb_enabled;
> + /* Shared memory region for mappings. */
> + QSIMPLEQ_HEAD(, VirtioSharedMemory) shmem_list;
> };
>
> struct VirtioDeviceClass {
> @@ -298,6 +339,100 @@ void virtio_notify(VirtIODevice *vdev, VirtQueue *vq);
>
> int virtio_save(VirtIODevice *vdev, QEMUFile *f);
>
> +/**
> + * virtio_new_shmem_region() - Create a new shared memory region
> + * @vdev: VirtIODevice
> + * @shmid: Shared memory ID
> + * @size: Size of the shared memory region
> + *
> + * Creates a new VirtioSharedMemory region for the given device and ID.
> + * The returned VirtioSharedMemory is owned by the VirtIODevice and will
> + * be automatically freed when the device is destroyed. The caller
> + * should not free the returned pointer.
> + *
> + * Returns: Pointer to the new VirtioSharedMemory region, or NULL on failure
> + */
> +VirtioSharedMemory *virtio_new_shmem_region(VirtIODevice *vdev, uint8_t
> shmid, uint64_t size);
> +
> +/**
> + * virtio_find_shmem_region() - Find an existing shared memory region
> + * @vdev: VirtIODevice
> + * @shmid: Shared memory ID to find
> + *
> + * Finds an existing VirtioSharedMemory region by ID. The returned pointer
> + * is owned by the VirtIODevice and should not be freed by the caller.
> + *
> + * Returns: Pointer to the VirtioSharedMemory region, or NULL if not found
> + */
> +VirtioSharedMemory *virtio_find_shmem_region(VirtIODevice *vdev, uint8_t
> shmid);
> +
> +/**
> + * virtio_shared_memory_mapping_new() - Create a new
> VirtioSharedMemoryMapping
> + * @shmid: VIRTIO Shared Memory Region ID
> + * @fd: File descriptor for the shared memory
> + * @fd_offset: Offset within the file descriptor
> + * @shm_offset: Offset within the VIRTIO Shared Memory Region
> + * @len: Size of the mapping
> + * @allow_write: Whether to allow write access to the mapping
> + *
> + * Creates a new VirtioSharedMemoryMapping that manages a shared memory
> mapping.
> + * The object will create a MemoryRegion using
> memory_region_init_ram_from_fd()
> + * as a child object. When the object is finalized, it will automatically
> + * clean up the MemoryRegion and close the file descriptor.
> + *
> + * Return: A new VirtioSharedMemoryMapping on success, NULL on error.
> + */
> +VirtioSharedMemoryMapping *virtio_shared_memory_mapping_new(uint8_t shmid,
> + int fd,
> + uint64_t
> fd_offset,
> + uint64_t
> shm_offset,
> + uint64_t len,
> + bool
> allow_write);
> +
> +/**
> + * virtio_add_shmem_map() - Add a memory mapping to a shared region
> + * @shmem: VirtioSharedMemory region
> + * @mapping: VirtioSharedMemoryMapping to add (transfers ownership)
> + *
> + * Adds a memory mapping to the shared memory region. The
> VirtioSharedMemoryMapping
> + * ownership is transferred to the shared memory region and will be
> automatically
> + * cleaned up through QOM reference counting when virtio_del_shmem_map() is
> + * called or when the shared memory region is destroyed.
> + *
> + * Returns: 0 on success, negative errno on failure
> + */
> +int virtio_add_shmem_map(VirtioSharedMemory *shmem,
> + VirtioSharedMemoryMapping *mapping);
> +
> +/**
> + * virtio_find_shmem_map() - Find a memory mapping in a shared region
> + * @shmem: VirtioSharedMemory region
> + * @offset: Offset within the shared memory region
> + * @size: Size of the mapping to find
> + *
> + * Finds an existing memory mapping that covers the specified range.
> + * The returned VirtioSharedMemoryMapping is owned by the VirtioSharedMemory
> + * region and should not be freed by the caller.
> + *
> + * Returns: Pointer to the VirtioSharedMemoryMapping, or NULL if not found
> + */
> +VirtioSharedMemoryMapping *virtio_find_shmem_map(VirtioSharedMemory *shmem,
> + hwaddr offset, uint64_t size);
> +
> +/**
> + * virtio_del_shmem_map() - Remove a memory mapping from a shared region
> + * @shmem: VirtioSharedMemory region
> + * @offset: Offset of the mapping to remove
> + * @size: Size of the mapping to remove
> + *
> + * Removes a memory mapping from the shared memory region. This will
> + * automatically unref the associated VhostUserShmemObject, which may
> + * trigger its finalization and cleanup if no other references exist.
> + * The mapping's MemoryRegion will be properly unmapped and cleaned up.
> + */
> +void virtio_del_shmem_map(VirtioSharedMemory *shmem, hwaddr offset,
> + uint64_t size);
> +
> extern const VMStateInfo virtio_vmstate_info;
>
> #define VMSTATE_VIRTIO_DEVICE \
> diff --git a/subprojects/libvhost-user/libvhost-user.c
> b/subprojects/libvhost-user/libvhost-user.c
> index 9c630c2170..034cbfdc3c 100644
> --- a/subprojects/libvhost-user/libvhost-user.c
> +++ b/subprojects/libvhost-user/libvhost-user.c
> @@ -1592,6 +1592,76 @@ vu_rm_shared_object(VuDev *dev, unsigned char
> uuid[UUID_LEN])
> return vu_send_message(dev, &msg);
> }
>
> +bool
> +vu_shmem_map(VuDev *dev, uint8_t shmid, uint64_t fd_offset,
> + uint64_t shm_offset, uint64_t len, uint64_t flags, int fd)
> +{
> + VhostUserMsg vmsg = {
> + .request = VHOST_USER_BACKEND_SHMEM_MAP,
> + .size = sizeof(vmsg.payload.mmap),
> + .flags = VHOST_USER_VERSION,
> + .payload.mmap = {
> + .shmid = shmid,
> + .fd_offset = fd_offset,
> + .shm_offset = shm_offset,
> + .len = len,
> + .flags = flags,
> + },
> + .fd_num = 1,
> + .fds[0] = fd,
> + };
> +
> + if (!vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SHMEM)) {
> + return false;
> + }
> +
> + if (vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_REPLY_ACK)) {
> + vmsg.flags |= VHOST_USER_NEED_REPLY_MASK;
> + }
> +
> + pthread_mutex_lock(&dev->backend_mutex);
> + if (!vu_message_write(dev, dev->backend_fd, &vmsg)) {
> + pthread_mutex_unlock(&dev->backend_mutex);
> + return false;
> + }
> +
> + /* Also unlocks the backend_mutex */
> + return vu_process_message_reply(dev, &vmsg);
> +}
> +
> +bool
> +vu_shmem_unmap(VuDev *dev, uint8_t shmid, uint64_t shm_offset, uint64_t len)
> +{
> + VhostUserMsg vmsg = {
> + .request = VHOST_USER_BACKEND_SHMEM_UNMAP,
> + .size = sizeof(vmsg.payload.mmap),
> + .flags = VHOST_USER_VERSION,
> + .payload.mmap = {
> + .shmid = shmid,
> + .fd_offset = 0,
> + .shm_offset = shm_offset,
> + .len = len,
> + },
> + };
> +
> + if (!vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SHMEM)) {
> + return false;
> + }
> +
> + if (vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_REPLY_ACK)) {
> + vmsg.flags |= VHOST_USER_NEED_REPLY_MASK;
> + }
> +
> + pthread_mutex_lock(&dev->backend_mutex);
> + if (!vu_message_write(dev, dev->backend_fd, &vmsg)) {
> + pthread_mutex_unlock(&dev->backend_mutex);
> + return false;
> + }
> +
> + /* Also unlocks the backend_mutex */
> + return vu_process_message_reply(dev, &vmsg);
> +}
> +
> static bool
> vu_set_vring_call_exec(VuDev *dev, VhostUserMsg *vmsg)
> {
> diff --git a/subprojects/libvhost-user/libvhost-user.h
> b/subprojects/libvhost-user/libvhost-user.h
> index 2ffc58c11b..6a2d0f9fae 100644
> --- a/subprojects/libvhost-user/libvhost-user.h
> +++ b/subprojects/libvhost-user/libvhost-user.h
> @@ -69,6 +69,8 @@ enum VhostUserProtocolFeature {
> /* Feature 16 is reserved for VHOST_USER_PROTOCOL_F_STATUS. */
> /* Feature 17 reserved for VHOST_USER_PROTOCOL_F_XEN_MMAP. */
> VHOST_USER_PROTOCOL_F_SHARED_OBJECT = 18,
> + /* Feature 19 is reserved for VHOST_USER_PROTOCOL_F_DEVICE_STATE */
> + VHOST_USER_PROTOCOL_F_SHMEM = 20,
> VHOST_USER_PROTOCOL_F_MAX
> };
>
> @@ -127,6 +129,8 @@ typedef enum VhostUserBackendRequest {
> VHOST_USER_BACKEND_SHARED_OBJECT_ADD = 6,
> VHOST_USER_BACKEND_SHARED_OBJECT_REMOVE = 7,
> VHOST_USER_BACKEND_SHARED_OBJECT_LOOKUP = 8,
> + VHOST_USER_BACKEND_SHMEM_MAP = 9,
> + VHOST_USER_BACKEND_SHMEM_UNMAP = 10,
> VHOST_USER_BACKEND_MAX
> } VhostUserBackendRequest;
>
> @@ -186,6 +190,23 @@ typedef struct VhostUserShared {
> unsigned char uuid[UUID_LEN];
> } VhostUserShared;
>
> +/* For the flags field of VhostUserMMap */
> +#define VHOST_USER_FLAG_MAP_RW (1u << 0)
> +
> +typedef struct {
> + /* VIRTIO Shared Memory Region ID */
> + uint8_t shmid;
> + uint8_t padding[7];
> + /* File offset */
> + uint64_t fd_offset;
> + /* Offset within the VIRTIO Shared Memory Region */
> + uint64_t shm_offset;
> + /* Size of the mapping */
> + uint64_t len;
> + /* Flags for the mmap operation, from VHOST_USER_FLAG_MAP_* */
> + uint64_t flags;
> +} VhostUserMMap;
> +
> #define VU_PACKED __attribute__((packed))
>
> typedef struct VhostUserMsg {
> @@ -210,6 +231,7 @@ typedef struct VhostUserMsg {
> VhostUserVringArea area;
> VhostUserInflight inflight;
> VhostUserShared object;
> + VhostUserMMap mmap;
> } payload;
>
> int fds[VHOST_MEMORY_BASELINE_NREGIONS];
> @@ -593,6 +615,38 @@ bool vu_add_shared_object(VuDev *dev, unsigned char
> uuid[UUID_LEN]);
> */
> bool vu_rm_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN]);
>
> +/**
> + * vu_shmem_map:
> + * @dev: a VuDev context
> + * @shmid: VIRTIO Shared Memory Region ID
> + * @fd_offset: File offset
> + * @shm_offset: Offset within the VIRTIO Shared Memory Region
> + * @len: Size of the mapping
> + * @flags: Flags for the mmap operation
> + * @fd: A file descriptor
> + *
> + * Advertises a new mapping to be made in a given VIRTIO Shared Memory
> Region.
> + *
> + * Returns: TRUE on success, FALSE on failure.
> + */
> +bool vu_shmem_map(VuDev *dev, uint8_t shmid, uint64_t fd_offset,
> + uint64_t shm_offset, uint64_t len, uint64_t flags, int fd);
> +
> +/**
> + * vu_shmem_unmap:
> + * @dev: a VuDev context
> + * @shmid: VIRTIO Shared Memory Region ID
> + * @fd_offset: File offset
> + * @len: Size of the mapping
> + *
> + * The front-end un-mmaps a given range in the VIRTIO Shared Memory Region
> + * with the requested `shmid`.
> + *
> + * Returns: TRUE on success, FALSE on failure.
> + */
> +bool vu_shmem_unmap(VuDev *dev, uint8_t shmid, uint64_t shm_offset,
> + uint64_t len);
> +
> /**
> * vu_queue_set_notification:
> * @dev: a VuDev context
> --
> 2.49.0
