[PATCH v3 1/5] vhost-user: Add VIRTIO Shared Memory map request

[Albert Esteve <aesteve@redhat.com>]

Add SHMEM_MAP/UNMAP requests to vhost-user to
handle VIRTIO Shared Memory mappings.

This request allows backends to dynamically map
fds into a VIRTIO Shared Memory Region indentified
by its `shmid`. Then, the fd memory is advertised
to the driver as a base addres + offset, so it
can be read/written (depending on the mmap flags
requested) while its valid.

The backend can munmap the memory range
in a given VIRTIO Shared Memory Region (again,
identified by its `shmid`), to free it. Upon
receiving this message, the front-end must
mmap the regions with PROT_NONE to reserve
the virtual memory space.

The device model needs to create MemoryRegion
instances for the VIRTIO Shared Memory Regions
and add them to the `VirtIODevice` instance.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 hw/virtio/vhost-user.c                    | 122 ++++++++++++++++++++++
 hw/virtio/virtio.c                        |  13 +++
 include/hw/virtio/virtio.h                |   5 +
 subprojects/libvhost-user/libvhost-user.c |  60 +++++++++++
 subprojects/libvhost-user/libvhost-user.h |  52 +++++++++
 5 files changed, 252 insertions(+)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 00561daa06..338cc942ec 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -115,6 +115,8 @@ 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;
 
@@ -192,6 +194,24 @@ typedef struct VhostUserShared {
     unsigned char uuid[16];
 } VhostUserShared;
 
+/* For the flags field of VhostUserMMap */
+#define VHOST_USER_FLAG_MAP_R (1u << 0)
+#define VHOST_USER_FLAG_MAP_W (1u << 1)
+
+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_* */
+    uint64_t flags;
+} VhostUserMMap;
+
 typedef struct {
     VhostUserRequest request;
 
@@ -224,6 +244,7 @@ typedef union {
         VhostUserInflight inflight;
         VhostUserShared object;
         VhostUserTransferDeviceState transfer_state;
+        VhostUserMMap mmap;
 } VhostUserPayload;
 
 typedef struct VhostUserMsg {
@@ -1749,6 +1770,100 @@ vhost_user_backend_handle_shared_object_lookup(struct vhost_user *u,
     return 0;
 }
 
+static int
+vhost_user_backend_handle_shmem_map(struct vhost_dev *dev,
+                                    VhostUserMMap *vu_mmap,
+                                    int fd)
+{
+    void *addr = 0;
+    MemoryRegion *mr = NULL;
+
+    if (fd < 0) {
+        error_report("Bad fd for map");
+        return -EBADF;
+    }
+
+    if (!dev->vdev->shmem_list ||
+        dev->vdev->n_shmem_regions <= vu_mmap->shmid) {
+        error_report("Device only has %d VIRTIO Shared Memory Regions. "
+                     "Requested ID: %d",
+                     dev->vdev->n_shmem_regions, vu_mmap->shmid);
+        return -EFAULT;
+    }
+
+    mr = &dev->vdev->shmem_list[vu_mmap->shmid];
+
+    if (!mr) {
+        error_report("VIRTIO Shared Memory Region at "
+                     "ID %d unitialized", vu_mmap->shmid);
+        return -EFAULT;
+    }
+
+    if ((vu_mmap->shm_offset + vu_mmap->len) < vu_mmap->len ||
+        (vu_mmap->shm_offset + vu_mmap->len) > mr->size) {
+        error_report("Bad offset/len for mmap %" PRIx64 "+%" PRIx64,
+                     vu_mmap->shm_offset, vu_mmap->len);
+        return -EFAULT;
+    }
+
+    void *shmem_ptr = memory_region_get_ram_ptr(mr);
+
+    addr = mmap(shmem_ptr + vu_mmap->shm_offset, vu_mmap->len,
+        ((vu_mmap->flags & VHOST_USER_FLAG_MAP_R) ? PROT_READ : 0) |
+        ((vu_mmap->flags & VHOST_USER_FLAG_MAP_W) ? PROT_WRITE : 0),
+        MAP_SHARED | MAP_FIXED, fd, vu_mmap->fd_offset);
+
+    if (addr == MAP_FAILED) {
+        error_report("Failed to mmap mem fd");
+        return -EFAULT;
+    }
+
+    return 0;
+}
+
+static int
+vhost_user_backend_handle_shmem_unmap(struct vhost_dev *dev,
+                                      VhostUserMMap *vu_mmap)
+{
+    void *addr = 0;
+    MemoryRegion *mr = NULL;
+
+    if (!dev->vdev->shmem_list ||
+        dev->vdev->n_shmem_regions <= vu_mmap->shmid) {
+        error_report("Device only has %d VIRTIO Shared Memory Regions. "
+                     "Requested ID: %d",
+                     dev->vdev->n_shmem_regions, vu_mmap->shmid);
+        return -EFAULT;
+    }
+
+    mr = &dev->vdev->shmem_list[vu_mmap->shmid];
+
+    if (!mr) {
+        error_report("VIRTIO Shared Memory Region at "
+                     "ID %d unitialized", vu_mmap->shmid);
+        return -EFAULT;
+    }
+
+    if ((vu_mmap->shm_offset + vu_mmap->len) < vu_mmap->len ||
+        (vu_mmap->shm_offset + vu_mmap->len) > mr->size) {
+        error_report("Bad offset/len for mmap %" PRIx64 "+%" PRIx64,
+                     vu_mmap->shm_offset, vu_mmap->len);
+        return -EFAULT;
+    }
+
+    void *shmem_ptr = memory_region_get_ram_ptr(mr);
+
+    addr = mmap(shmem_ptr + vu_mmap->shm_offset, vu_mmap->len,
+                PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
+
+    if (addr == MAP_FAILED) {
+        error_report("Failed to unmap memory");
+        return -EFAULT;
+    }
+
+    return 0;
+}
+
 static void close_backend_channel(struct vhost_user *u)
 {
     g_source_destroy(u->backend_src);
@@ -1817,6 +1932,13 @@ static gboolean backend_read(QIOChannel *ioc, GIOCondition condition,
         ret = vhost_user_backend_handle_shared_object_lookup(dev->opaque, ioc,
                                                              &hdr, &payload);
         break;
+    case VHOST_USER_BACKEND_SHMEM_MAP:
+        ret = vhost_user_backend_handle_shmem_map(dev, &payload.mmap,
+                                                  fd ? fd[0] : -1);
+        break;
+    case VHOST_USER_BACKEND_SHMEM_UNMAP:
+        ret = vhost_user_backend_handle_shmem_unmap(dev, &payload.mmap);
+        break;
     default:
         error_report("Received unexpected msg type: %d.", hdr.request);
         ret = -EINVAL;
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 9e10cbc058..ccc4f2cd75 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -3059,6 +3059,17 @@ int virtio_save(VirtIODevice *vdev, QEMUFile *f)
     return vmstate_save_state(f, &vmstate_virtio, vdev, NULL);
 }
 
+MemoryRegion *virtio_new_shmem_region(VirtIODevice *vdev)
+{
+    MemoryRegion *mr;
+    ++vdev->n_shmem_regions;
+    vdev->shmem_list = g_renew(MemoryRegion, vdev->shmem_list,
+                               vdev->n_shmem_regions);
+    mr = &vdev->shmem_list[vdev->n_shmem_regions - 1];
+    mr = g_new0(MemoryRegion, 1);
+    return mr;
+}
+
 /* 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)
@@ -3481,6 +3492,8 @@ void virtio_init(VirtIODevice *vdev, uint16_t device_id, size_t config_size)
             virtio_vmstate_change, vdev);
     vdev->device_endian = virtio_default_endian();
     vdev->use_guest_notifier_mask = true;
+    vdev->shmem_list = NULL;
+    vdev->n_shmem_regions = 0;
 }
 
 /*
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 0fcbc5c0c6..d4a2f664d9 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -167,6 +167,9 @@ struct VirtIODevice
      */
     EventNotifier config_notifier;
     bool device_iotlb_enabled;
+    /* Shared memory region for vhost-user mappings. */
+    MemoryRegion *shmem_list;
+    int n_shmem_regions;
 };
 
 struct VirtioDeviceClass {
@@ -286,6 +289,8 @@ void virtio_notify(VirtIODevice *vdev, VirtQueue *vq);
 
 int virtio_save(VirtIODevice *vdev, QEMUFile *f);
 
+MemoryRegion *virtio_new_shmem_region(VirtIODevice *vdev);
+
 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..496268e12b 100644
--- a/subprojects/libvhost-user/libvhost-user.c
+++ b/subprojects/libvhost-user/libvhost-user.c
@@ -1592,6 +1592,66 @@ 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)
+{
+    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,
+        },
+    };
+
+    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_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 deb40e77b3..ea4902e876 100644
--- a/subprojects/libvhost-user/libvhost-user.h
+++ b/subprojects/libvhost-user/libvhost-user.h
@@ -127,6 +127,8 @@ 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 +188,24 @@ typedef struct VhostUserShared {
     unsigned char uuid[UUID_LEN];
 } VhostUserShared;
 
+/* For the flags field of VhostUserMMap */
+#define VHOST_USER_FLAG_MAP_R (1u << 0)
+#define VHOST_USER_FLAG_MAP_W (1u << 1)
+
+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_* */
+    uint64_t flags;
+} VhostUserMMap;
+
 #if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
 # define VU_PACKED __attribute__((gcc_struct, packed))
 #else
@@ -214,6 +234,7 @@ typedef struct VhostUserMsg {
         VhostUserVringArea area;
         VhostUserInflight inflight;
         VhostUserShared object;
+        VhostUserMMap mmap;
     } payload;
 
     int fds[VHOST_MEMORY_BASELINE_NREGIONS];
@@ -597,6 +618,37 @@ 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
+ *
+ * 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);
+
+/**
+ * vu_shmem_map:
+ * @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
-- 
2.45.2