On Tue, Sep 3, 2024 at 11:54 AM Albert Esteve <aest...@redhat.com> wrote:
>
>
> On Thu, Jul 11, 2024 at 9:45 AM Stefan Hajnoczi <stefa...@redhat.com>
> wrote:
>
>> On Fri, Jun 28, 2024 at 04:57:06PM +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 <aest...@redhat.com>
>> > ---
>> > docs/interop/vhost-user.rst | 27 +++++
>> > hw/virtio/vhost-user.c | 122 ++++++++++++++++++++++
>> > hw/virtio/virtio.c | 12 +++
>> > include/hw/virtio/virtio.h | 5 +
>> > subprojects/libvhost-user/libvhost-user.c | 65 ++++++++++++
>> > subprojects/libvhost-user/libvhost-user.h | 53 ++++++++++
>> > 6 files changed, 284 insertions(+)
>> >
>> > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
>> > index d8419fd2f1..d52ba719d5 100644
>> > --- a/docs/interop/vhost-user.rst
>> > +++ b/docs/interop/vhost-user.rst
>> > @@ -1859,6 +1859,33 @@ is sent by the front-end.
>> > when the operation is successful, or non-zero otherwise. Note that
>> if the
>> > operation fails, no fd is sent to the backend.
>> >
>> > +``VHOST_USER_BACKEND_SHMEM_MAP``
>> > + :id: 9
>> > + :equivalent ioctl: N/A
>> > + :request payload: fd and ``struct VhostUserMMap``
>> > + :reply payload: N/A
>> > +
>> > + This message can be submitted by the backends to advertise a new
>> mapping
>> > + to be made in a given VIRTIO Shared Memory Region. Upon receiving
>> the message,
>> > + The front-end will mmap the given fd into the VIRTIO Shared Memory
>> Region
>> > + with the requested ``shmid``. A reply is generated indicating
>> whether mapping
>> > + succeeded.
>> > +
>> > + Mapping over an already existing map is not allowed and request
>> shall fail.
>> > + Therefore, the memory range in the request must correspond with a
>> valid,
>> > + free region of the VIRTIO Shared Memory Region.
>> > +
>> > +``VHOST_USER_BACKEND_SHMEM_UNMAP``
>> > + :id: 10
>> > + :equivalent ioctl: N/A
>> > + :request payload: ``struct VhostUserMMap``
>> > + :reply payload: N/A
>> > +
>> > + This message can be submitted by the backends so that the front-end
>> un-mmap
>> > + a given range (``offset``, ``len``) in the VIRTIO Shared Memory
>> Region with
>>
>> s/offset/shm_offset/
>>
>> > + the requested ``shmid``.
>>
>> Please clarify that <offset, len> must correspond to the entirety of a
>> valid mapped region.
>>
>> By the way, the VIRTIO 1.3 gives the following behavior for the virtiofs
>> DAX Window:
>>
>> When a FUSE_SETUPMAPPING request perfectly overlaps a previous
>> mapping, the previous mapping is replaced. When a mapping partially
>> overlaps a previous mapping, the previous mapping is split into one or
>> two smaller mappings. When a mapping is partially unmapped it is also
>> split into one or two smaller mappings.
>>
>> Establishing new mappings or splitting existing mappings consumes
>> resources. If the device runs out of resources the FUSE_SETUPMAPPING
>> request fails until resources are available again following
>> FUSE_REMOVEMAPPING.
>>
>> I think SETUPMAPPING/REMOVMAPPING can be implemented using
>> SHMEM_MAP/UNMAP. SHMEM_MAP/UNMAP do not allow atomically replacing
>> partial ranges, but as far as I know that's not necessary for virtiofs
>> in practice.
>>
>> It's worth mentioning that mappings consume resources and that SHMEM_MAP
>> can fail when there are no resources available. The process-wide limit
>> is vm.max_map_count on Linux although a vhost-user frontend may reduce
>> it further to control vhost-user resource usage.
>>
>> > + A reply is generated indicating whether unmapping succeeded.
>> > +
>> > .. _reply_ack:
>> >
>> > VHOST_USER_PROTOCOL_F_REPLY_ACK
>> > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
>> > index cdf9af4a4b..7ee8a472c6 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 {
>> > @@ -1748,6 +1769,100 @@
>> 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,
>>
>> Missing check for overlap between range [shm_offset, shm_offset + len)
>> and existing mappings.
>>
>
> Not sure how to do this check. Specifically, I am not sure how previous
> ranges are stored within the MemoryRegion. Is looping through
> mr->subregions
> a valid option?
>
Maybe something like this would do?
```
if (memory_region_find(mr, vu_mmap->shm_offset, vu_mmap->len).mr) {
error_report("Requested memory (%" PRIx64 "+%" PRIx64 " overalps "
"with previously mapped memory",
vu_mmap->shm_offset, vu_mmap->len);
return -EFAULT;
}
```
>
>
>>
>> > + ((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,
>>
>> Missing check for existing mapping with exact range [shm_offset, len)
>> match.
>>
>> > + 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);
>> > @@ -1816,6 +1931,13 @@ 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 893a072c9d..9f2da5b11e 100644
>> > --- a/hw/virtio/virtio.c
>> > +++ b/hw/virtio/virtio.c
>> > @@ -2856,6 +2856,16 @@ 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 = g_new0(MemoryRegion, 1);
>> > + ++vdev->n_shmem_regions;
>> > + vdev->shmem_list = g_renew(MemoryRegion, vdev->shmem_list,
>> > + vdev->n_shmem_regions);
>>
>> Where is shmem_list freed?
>>
>> The name "list" is misleading since this is an array, not a list.
>>
>> > + vdev->shmem_list[vdev->n_shmem_regions - 1] = *mr;
>> > + return mr;
>> > +}
>>
>> This looks weird. The contents of mr are copied into shmem_list[] and
>> then the pointer to mr is returned? Did you mean for the field's type to
>> be MemoryRegion **shmem_list and then vdev->shmem_list[...] = mr would
>> stash the pointer?
>>
>> > +
>> > /* 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)
>> > @@ -3264,6 +3274,8 @@ 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 7d5ffdc145..16d598aadc 100644
>> > --- a/include/hw/virtio/virtio.h
>> > +++ b/include/hw/virtio/virtio.h
>> > @@ -165,6 +165,9 @@ 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 {
>> > @@ -280,6 +283,8 @@ 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 a879149fef..28556d183a 100644
>> > --- a/subprojects/libvhost-user/libvhost-user.c
>> > +++ b/subprojects/libvhost-user/libvhost-user.c
>> > @@ -1586,6 +1586,71 @@ 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)
>> > +{
>> > + bool result = false;
>> > + VhostUserMsg msg_reply;
>> > + 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 fd_offset,
>> > + uint64_t shm_offset, uint64_t len)
>> > +{
>> > + bool result = false;
>> > + VhostUserMsg msg_reply;
>> > + VhostUserMsg vmsg = {
>> > + .request = VHOST_USER_BACKEND_SHMEM_UNMAP,
>> > + .size = sizeof(vmsg.payload.mmap),
>> > + .flags = VHOST_USER_VERSION,
>> > + .payload.mmap = {
>> > + .shmid = shmid,
>> > + .fd_offset = fd_offset,
>>
>> What is the meaning of this field? I expected it to be set to 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..7f6c22cc1a 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 +618,38 @@ 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
>> > + *
>> > + * 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
>> > + * @shm_offset: Offset within the VIRTIO Shared Memory Region
>> > + * @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 fd_offset,
>> > + uint64_t shm_offset, uint64_t len);
>> > +
>> > /**
>> > * vu_queue_set_notification:
>> > * @dev: a VuDev context
>> > --
>> > 2.45.2
>> >
>>
>
