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

[Yongji Xie <xieyongji@bytedance.com>]

On Fri, Dec 25, 2020 at 3:02 PM Jason Wang <jasowang@redhat.com> wrote:
>
>
> On 2020/12/25 上午10:37, Yongji Xie wrote:
> > On Thu, Dec 24, 2020 at 3:37 PM Yongji Xie <xieyongji@bytedance.com> wrote:
> >> 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?
> >>
> > Oh sorry, looks like mmap() needs to be called in IOTLB UPDATE message
> > handler. Is it possible for the vdpa device to know which vdpa bus it
> > is attached to?
>
>
> We'd better not. It's kind of layer violation.
>

OK. Now I think both ioctl and message are needed. The ioctl is useful
when VDUSE userspace daemon reboot. And the IOTLB_UPDATE message could
be generated during the first DMA mapping in the virtio-vdpa case.

Thanks,
Yongji