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

[Yongji Xie <xieyongji@bytedance.com>]

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.

>
> > +     vduse_dev_msg_put(msg);
> > +     fput(file);
> > +
> > +     return ret;
> > +}
> > +
> > +static int vduse_dev_invalidate_iotlb(struct vduse_dev *dev,
> > +                                     u64 iova, u64 size)
> > +{
> > +     struct vduse_dev_msg *msg;
> > +     int ret;
> > +
> > +     if (!size)
> > +             return -EINVAL;
> > +
> > +     msg = vduse_dev_new_msg(dev, VDUSE_INVALIDATE_IOTLB);
> > +     msg->req.size = sizeof(struct vduse_iotlb);
> > +     msg->req.iotlb.iova = iova;
> > +     msg->req.iotlb.size = size;
> > +
> > +     ret = vduse_dev_msg_sync(dev, msg);
> > +     vduse_dev_msg_put(msg);
> > +
> > +     return ret;
> > +}
> > +
> > +static unsigned int perm_to_file_flags(u8 perm)
> > +{
> > +     unsigned int flags = 0;
> > +
> > +     switch (perm) {
> > +     case VHOST_ACCESS_WO:
> > +             flags |= O_WRONLY;
> > +             break;
> > +     case VHOST_ACCESS_RO:
> > +             flags |= O_RDONLY;
> > +             break;
> > +     case VHOST_ACCESS_RW:
> > +             flags |= O_RDWR;
> > +             break;
> > +     default:
> > +             WARN(1, "invalidate vhost IOTLB permission\n");
> > +             break;
> > +     }
> > +
> > +     return flags;
> > +}
> > +
> >   static ssize_t vduse_dev_read_iter(struct kiocb *iocb, struct iov_iter *to)
> >   {
> >       struct file *file = iocb->ki_filp;
> >       struct vduse_dev *dev = file->private_data;
> >       struct vduse_dev_msg *msg;
> > -     int size = sizeof(struct vduse_dev_request);
> > +     unsigned int flags;
> > +     int fd, size = sizeof(struct vduse_dev_request);
> >       ssize_t ret = 0;
> >
> >       if (iov_iter_count(to) < size)
> > @@ -349,6 +418,18 @@ static ssize_t vduse_dev_read_iter(struct kiocb *iocb, struct iov_iter *to)
> >               if (ret)
> >                       return ret;
> >       }
> > +
> > +     if (msg->req.type == VDUSE_UPDATE_IOTLB && msg->req.iotlb.fd == -1) {
> > +             flags = perm_to_file_flags(msg->req.iotlb.perm);
> > +             fd = get_unused_fd_flags(flags);
> > +             if (fd < 0) {
> > +                     vduse_dev_enqueue_msg(dev, msg, &dev->send_list);
> > +                     return fd;
> > +             }
> > +             fd_install(fd, get_file(msg->iotlb_file));
> > +             msg->req.iotlb.fd = fd;
> > +     }
> > +
> >       ret = copy_to_iter(&msg->req, size, to);
> >       if (ret != size) {
> >               vduse_dev_enqueue_msg(dev, msg, &dev->send_list);
> > @@ -565,6 +646,69 @@ static void vduse_vdpa_set_config(struct vdpa_device *vdpa, unsigned int offset,
> >       vduse_dev_set_config(dev, offset, buf, len);
> >   }
> >
> > +static void vduse_vdpa_invalidate_iotlb(struct vduse_dev *dev,
> > +                                     struct vhost_iotlb_msg *msg)
> > +{
> > +     vduse_dev_invalidate_iotlb(dev, msg->iova, msg->size);
> > +}
> > +
> > +static int vduse_vdpa_update_iotlb(struct vduse_dev *dev,
> > +                                     struct vhost_iotlb_msg *msg)
> > +{
> > +     u64 uaddr = msg->uaddr;
> > +     u64 iova = msg->iova;
> > +     u64 size = msg->size;
> > +     u64 offset;
> > +     struct vm_area_struct *vma;
> > +     int ret;
> > +
> > +     while (uaddr < msg->uaddr + msg->size) {
> > +             vma = find_vma(current->mm, uaddr);
> > +             ret = -EINVAL;
> > +             if (!vma)
> > +                     goto err;
> > +
> > +             size = min(msg->size, vma->vm_end - uaddr);
> > +             offset = (vma->vm_pgoff << PAGE_SHIFT) + uaddr - vma->vm_start;
> > +             if (vma->vm_file && (vma->vm_flags & VM_SHARED)) {
> > +                     ret = vduse_dev_update_iotlb(dev, vma->vm_file, offset,
> > +                                                     iova, size, msg->perm);
> > +                     if (ret)
> > +                             goto err;
>
>
> My understanding is that vma is something that should not be known by a
> device. So I suggest to move the above processing to vhost-vdpa.c.
>

Will do it.

Thanks,
Yongji