Re: Re: [RFC v2 09/13] vduse: Add support for processing vhost iotlb message

[Yongji Xie <xieyongji@bytedance.com>]

On Thu, Dec 24, 2020 at 10:41 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> On 2020/12/23 下午8:14, Yongji Xie wrote:
> > On Wed, Dec 23, 2020 at 5:05 PM Jason Wang <jasowang@redhat.com> wrote:
> >>
> >> On 2020/12/22 下午10:52, Xie Yongji wrote:
> >>> To support vhost-vdpa bus driver, we need a way to share the
> >>> vhost-vdpa backend process's memory with the userspace VDUSE process.
> >>>
> >>> This patch tries to make use of the vhost iotlb message to achieve
> >>> that. We will get the shm file from the iotlb message and pass it
> >>> to the userspace VDUSE process.
> >>>
> >>> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> >>> ---
> >>>    Documentation/driver-api/vduse.rst |  15 +++-
> >>>    drivers/vdpa/vdpa_user/vduse_dev.c | 147 ++++++++++++++++++++++++++++++++++++-
> >>>    include/uapi/linux/vduse.h         |  11 +++
> >>>    3 files changed, 171 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/Documentation/driver-api/vduse.rst b/Documentation/driver-api/vduse.rst
> >>> index 623f7b040ccf..48e4b1ba353f 100644
> >>> --- a/Documentation/driver-api/vduse.rst
> >>> +++ b/Documentation/driver-api/vduse.rst
> >>> @@ -46,13 +46,26 @@ The following types of messages are provided by the VDUSE framework now:
> >>>
> >>>    - VDUSE_GET_CONFIG: Read from device specific configuration space
> >>>
> >>> +- VDUSE_UPDATE_IOTLB: Update the memory mapping in device IOTLB
> >>> +
> >>> +- VDUSE_INVALIDATE_IOTLB: Invalidate the memory mapping in device IOTLB
> >>> +
> >>>    Please see include/linux/vdpa.h for details.
> >>>
> >>> -In the data path, VDUSE framework implements a MMU-based on-chip IOMMU
> >>> +The data path of userspace vDPA device is implemented in different ways
> >>> +depending on the vdpa bus to which it is attached.
> >>> +
> >>> +In virtio-vdpa case, VDUSE framework implements a MMU-based on-chip IOMMU
> >>>    driver which supports mapping the kernel dma buffer to a userspace iova
> >>>    region dynamically. The userspace iova region can be created by passing
> >>>    the userspace vDPA device fd to mmap(2).
> >>>
> >>> +In vhost-vdpa case, the dma buffer is reside in a userspace memory region
> >>> +which will be shared to the VDUSE userspace processs via the file
> >>> +descriptor in VDUSE_UPDATE_IOTLB message. And the corresponding address
> >>> +mapping (IOVA of dma buffer <-> VA of the memory region) is also included
> >>> +in this message.
> >>> +
> >>>    Besides, the eventfd mechanism is used to trigger interrupt callbacks and
> >>>    receive virtqueue kicks in userspace. The following ioctls on the userspace
> >>>    vDPA device fd are provided to support that:
> >>> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> >>> index b974333ed4e9..d24aaacb6008 100644
> >>> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> >>> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> >>> @@ -34,6 +34,7 @@
> >>>
> >>>    struct vduse_dev_msg {
> >>>        struct vduse_dev_request req;
> >>> +     struct file *iotlb_file;
> >>>        struct vduse_dev_response resp;
> >>>        struct list_head list;
> >>>        wait_queue_head_t waitq;
> >>> @@ -325,12 +326,80 @@ static int vduse_dev_set_vq_state(struct vduse_dev *dev,
> >>>        return ret;
> >>>    }
> >>>
> >>> +static int vduse_dev_update_iotlb(struct vduse_dev *dev, struct file *file,
> >>> +                             u64 offset, u64 iova, u64 size, u8 perm)
> >>> +{
> >>> +     struct vduse_dev_msg *msg;
> >>> +     int ret;
> >>> +
> >>> +     if (!size)
> >>> +             return -EINVAL;
> >>> +
> >>> +     msg = vduse_dev_new_msg(dev, VDUSE_UPDATE_IOTLB);
> >>> +     msg->req.size = sizeof(struct vduse_iotlb);
> >>> +     msg->req.iotlb.offset = offset;
> >>> +     msg->req.iotlb.iova = iova;
> >>> +     msg->req.iotlb.size = size;
> >>> +     msg->req.iotlb.perm = perm;
> >>> +     msg->req.iotlb.fd = -1;
> >>> +     msg->iotlb_file = get_file(file);
> >>> +
> >>> +     ret = vduse_dev_msg_sync(dev, msg);
> >>
> >> My feeling is that we should provide consistent API for the userspace
> >> device to use.
> >>
> >> E.g we'd better carry the IOTLB message for both virtio/vhost drivers.
> >>
> >> It looks to me for virtio drivers we can still use UPDAT_IOTLB message
> >> by using VDUSE file as msg->iotlb_file here.
> >>
> > It's OK for me. One problem is when to transfer the UPDATE_IOTLB
> > message in virtio cases.
>
>
> Instead of generating IOTLB messages for userspace.
>
> How about record the mappings (which is a common case for device have
> on-chip IOMMU e.g mlx5e and vdpa simlator), then we can introduce ioctl
> for userspace to query?
>

If so, the IOTLB UPDATE is actually triggered by ioctl, but
IOTLB_INVALIDATE is triggered by the message. Is it a little odd? Or
how about trigger it when userspace call mmap() on the device fd?

Thanks,
Yongji