* [PATCH v11 1/7] vhost-user: Add VirtIO Shared Memory map request
2025-11-11 9:10 [PATCH v11 0/7] vhost-user: Add SHMEM_MAP/UNMAP requests Albert Esteve
@ 2025-11-11 9:10 ` Albert Esteve
2025-11-11 9:10 ` [PATCH v11 2/7] vhost_user.rst: Align VhostUserMsg excerpt members Albert Esteve
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: Albert Esteve @ 2025-11-11 9:10 UTC (permalink / raw)
To: qemu-devel
Cc: dbassey, Michael S. Tsirkin, manos.pitsidianakis, slp, stefanha,
Fabiano Rosas, jasowang, Alex Bennée, Paolo Bonzini, david,
hi, stevensd, Stefano Garzarella, Laurent Vivier, Albert Esteve
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 <stefanha@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
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;
+ VirtioSharedMemoryMapping *mmap = NULL;
+ 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);
+ 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);
+ 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) {
+ /* Free the MemoryRegion only after reply */
+ virtio_del_shmem_map(shmem, vu_mmap->shm_offset, vu_mmap->len);
+ }
+
+ 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
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v11 7/7] vhost-user-device: Add shared memory BAR
2025-11-11 9:10 [PATCH v11 0/7] vhost-user: Add SHMEM_MAP/UNMAP requests Albert Esteve
` (5 preceding siblings ...)
2025-11-11 9:10 ` [PATCH v11 6/7] qmp: add shmem feature map Albert Esteve
@ 2025-11-11 9:10 ` Albert Esteve
6 siblings, 0 replies; 8+ messages in thread
From: Albert Esteve @ 2025-11-11 9:10 UTC (permalink / raw)
To: qemu-devel
Cc: dbassey, Michael S. Tsirkin, manos.pitsidianakis, slp, stefanha,
Fabiano Rosas, jasowang, Alex Bennée, Paolo Bonzini, david,
hi, stevensd, Stefano Garzarella, Laurent Vivier, Albert Esteve
Add shared memory BAR support to vhost-user-device-pci
to enable direct file mapping for VIRTIO Shared
Memory Regions.
The implementation creates a consolidated shared
memory BAR that contains all VIRTIO Shared
Memory Regions as subregions. Each region is
configured with its proper shmid, size, and
offset within the BAR. The number and size of
regions are retrieved via VHOST_USER_GET_SHMEM_CONFIG
message sent by vhost-user-base during realization
after virtio_init().
Specifiically, it uses BAR 3 to avoid conflicts, as
it is currently unused.
The shared memory BAR is only created when the
backend supports VHOST_USER_PROTOCOL_F_SHMEM and
has configured shared memory regions. This maintains
backward compatibility with backends that do not
support shared memory functionality.
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
hw/virtio/vhost-user-base.c | 47 ++++++++++++++++++++++++--
hw/virtio/vhost-user-test-device-pci.c | 39 +++++++++++++++++++--
2 files changed, 81 insertions(+), 5 deletions(-)
diff --git a/hw/virtio/vhost-user-base.c b/hw/virtio/vhost-user-base.c
index ff67a020b4..82f49500e4 100644
--- a/hw/virtio/vhost-user-base.c
+++ b/hw/virtio/vhost-user-base.c
@@ -16,6 +16,7 @@
#include "hw/virtio/virtio-bus.h"
#include "hw/virtio/vhost-user-base.h"
#include "qemu/error-report.h"
+#include "migration/blocker.h"
static void vub_start(VirtIODevice *vdev)
{
@@ -276,7 +277,9 @@ static void vub_device_realize(DeviceState *dev, Error **errp)
{
VirtIODevice *vdev = VIRTIO_DEVICE(dev);
VHostUserBase *vub = VHOST_USER_BASE(dev);
- int ret;
+ uint64_t memory_sizes[VIRTIO_MAX_SHMEM_REGIONS];
+ g_autofree char *name = NULL;
+ int i, ret, nregions, regions_processed = 0;
if (!vub->chardev.chr) {
error_setg(errp, "vhost-user-base: missing chardev");
@@ -319,7 +322,7 @@ static void vub_device_realize(DeviceState *dev, Error **errp)
/* Allocate queues */
vub->vqs = g_ptr_array_sized_new(vub->num_vqs);
- for (int i = 0; i < vub->num_vqs; i++) {
+ for (i = 0; i < vub->num_vqs; i++) {
g_ptr_array_add(vub->vqs,
virtio_add_queue(vdev, vub->vq_size,
vub_handle_output));
@@ -333,11 +336,49 @@ static void vub_device_realize(DeviceState *dev, Error **errp)
VHOST_BACKEND_TYPE_USER, 0, errp);
if (ret < 0) {
- do_vhost_user_cleanup(vdev, vub);
+ goto err;
+ }
+
+ ret = vub->vhost_dev.vhost_ops->vhost_get_shmem_config(&vub->vhost_dev,
+ &nregions,
+ memory_sizes,
+ errp);
+
+ if (ret < 0) {
+ goto err;
+ }
+
+ for (i = 0; i < VIRTIO_MAX_SHMEM_REGIONS && regions_processed < nregions; i++) {
+ if (memory_sizes[i]) {
+ regions_processed++;
+ if (vub->vhost_dev.migration_blocker == NULL) {
+ error_setg(&vub->vhost_dev.migration_blocker,
+ "Migration disabled: devices with VIRTIO Shared Memory "
+ "Regions do not support migration yet.");
+ ret = migrate_add_blocker_normal(
+ &vub->vhost_dev.migration_blocker,
+ errp);
+
+ if (ret < 0) {
+ goto err;
+ }
+ }
+
+ if (memory_sizes[i] % qemu_real_host_page_size() != 0) {
+ error_setg(errp, "Shared memory %d size must be a power of 2 "
+ "no smaller than the page size", i);
+ goto err;
+ }
+
+ virtio_new_shmem_region(vdev, i, memory_sizes[i]);
+ }
}
qemu_chr_fe_set_handlers(&vub->chardev, NULL, NULL, vub_event, NULL,
dev, NULL, true);
+ return;
+err:
+ do_vhost_user_cleanup(vdev, vub);
}
static void vub_device_unrealize(DeviceState *dev)
diff --git a/hw/virtio/vhost-user-test-device-pci.c b/hw/virtio/vhost-user-test-device-pci.c
index b4ed0efb50..d010cb3205 100644
--- a/hw/virtio/vhost-user-test-device-pci.c
+++ b/hw/virtio/vhost-user-test-device-pci.c
@@ -8,14 +8,18 @@
*/
#include "qemu/osdep.h"
+#include "qapi/error.h"
#include "hw/qdev-properties.h"
#include "hw/virtio/vhost-user-base.h"
#include "hw/virtio/virtio-pci.h"
+#define VIRTIO_DEVICE_PCI_SHMEM_BAR 4
+
struct VHostUserDevicePCI {
VirtIOPCIProxy parent_obj;
VHostUserBase vub;
+ MemoryRegion shmembar;
};
#define TYPE_VHOST_USER_TEST_DEVICE_PCI "vhost-user-test-device-pci-base"
@@ -25,10 +29,41 @@ OBJECT_DECLARE_SIMPLE_TYPE(VHostUserDevicePCI, VHOST_USER_TEST_DEVICE_PCI)
static void vhost_user_device_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
{
VHostUserDevicePCI *dev = VHOST_USER_TEST_DEVICE_PCI(vpci_dev);
- DeviceState *vdev = DEVICE(&dev->vub);
+ DeviceState *dev_state = DEVICE(&dev->vub);
+ VirtIODevice *vdev = VIRTIO_DEVICE(dev_state);
+ VirtioSharedMemory *shmem, *next;
+ uint64_t offset = 0, shmem_size = 0;
+ vpci_dev->modern_mem_bar_idx = 2;
vpci_dev->nvectors = 1;
- qdev_realize(vdev, BUS(&vpci_dev->bus), errp);
+ qdev_realize(dev_state, BUS(&vpci_dev->bus), errp);
+
+ QSIMPLEQ_FOREACH_SAFE(shmem, &vdev->shmem_list, entry, next) {
+ if (shmem->mr.size > UINT64_MAX - shmem_size) {
+ error_setg(errp, "Total shared memory required overflow");
+ return;
+ }
+ shmem_size = shmem_size + shmem->mr.size;
+ }
+ if (shmem_size) {
+ if (vpci_dev->flags & VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY) {
+ error_setg(errp, "modern-pio-notify is not supported due to PCI BAR layout limitations");
+ return;
+ }
+ memory_region_init(&dev->shmembar, OBJECT(vpci_dev),
+ "vhost-device-pci-shmembar", shmem_size);
+ QSIMPLEQ_FOREACH_SAFE(shmem, &vdev->shmem_list, entry, next) {
+ memory_region_add_subregion(&dev->shmembar, offset, &shmem->mr);
+ virtio_pci_add_shm_cap(vpci_dev, VIRTIO_DEVICE_PCI_SHMEM_BAR,
+ offset, shmem->mr.size, shmem->shmid);
+ offset = offset + shmem->mr.size;
+ }
+ pci_register_bar(&vpci_dev->pci_dev, VIRTIO_DEVICE_PCI_SHMEM_BAR,
+ PCI_BASE_ADDRESS_SPACE_MEMORY |
+ PCI_BASE_ADDRESS_MEM_PREFETCH |
+ PCI_BASE_ADDRESS_MEM_TYPE_64,
+ &dev->shmembar);
+ }
}
static void vhost_user_device_pci_class_init(ObjectClass *klass,
--
2.49.0
^ permalink raw reply related [flat|nested] 8+ messages in thread