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Re: [PATCH v3 1/5] vhost-user: Add VIRTIO Shared Memory map request
|
From: |
Stefan Hajnoczi |
|
Subject: |
Re: [PATCH v3 1/5] vhost-user: Add VIRTIO Shared Memory map request |
|
Date: |
Mon, 16 Sep 2024 19:21:30 +0200 |
On Thu, Sep 12, 2024 at 04:53:31PM +0200, Albert Esteve wrote:
> 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;
> +}
This function looks broken. shmem_list[] is reallocated so old
MemoryRegion pointers will be dangling pointers. And then the
MemoryRegion is allocated again using g_new0() but there is no way to
retrieve that address again via shmem_list[].
I expected something like this:
MemoryRegion *virtio_new_shmem_region(VirtIODevice *vdev)
{
MemoryRegion *mr;
assert(vdev->n_shmem_regions < INT_MAX);
++vdev->n_shmem_regions;
vdev->shmem_list = g_renew(MemoryRegion *, vdev->shmem_list,
vdev->n_shmem_regions);
mr = g_new0(MemoryRegion, 1);
vdev->shmem_list[vdev->n_shmem_regions - 1] = mr;
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;
shmem_list[] and each MemoryRegion needs to be free somewhere.
virtio_device_instance_finalize()?
> + 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);
How is the fd passed to the front-end?
> +
> +/**
> + * vu_shmem_map:
"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
> --
> 2.45.2
>
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