Re: [PATCH v5 5/5] media: virtio: Add USERPTR memory type support

On Mon, Aug 10, 2026 at 7:21 AM Laurent Pinchart
<[email protected]> wrote:
>
> On Thu, Jul 23, 2026 at 02:32:19PM -0400, Brian Daniels wrote:
> > From: Alexandre Courbot <[email protected]>
> >
> > This patch adds support for the USERPTR memory type to the virtio-media
> > driver.
> >
> > It adds the allow_userptr module parameter, implements the userptr
> > mapping logic in the scatterlist builder, and enables USERPTR in
> > reqbufs if allowed.
>
> USERPTR is deprecated, it shouldn't be used in new drivers or in new
> userspace code.

Good to know. Shall I remove this patch from the next revision then?

> > Signed-off-by: Alexandre Courbot <[email protected]>
> > Assisted-by: Antigravity:gemini-3.5-flash
> > Co-developed-by: Brian Daniels <[email protected]>
> > Signed-off-by: Brian Daniels <[email protected]>
> > ---
> >  drivers/media/virtio/scatterlist_builder.c | 64 ++++++++++++++++++++++
> >  drivers/media/virtio/scatterlist_builder.h |  3 +
> >  drivers/media/virtio/virtio_media_driver.c | 42 +++++++++-----
> >  drivers/media/virtio/virtio_media_ioctls.c | 11 +++-
> >  4 files changed, 104 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/media/virtio/scatterlist_builder.c b/drivers/media/virtio/scatterlist_builder.c
> > index 97925b277..85c6a36b4 100644
> > --- a/drivers/media/virtio/scatterlist_builder.c
> > +++ b/drivers/media/virtio/scatterlist_builder.c
> > @@ -349,14 +349,30 @@ static int scatterlist_builder_add_userptr(struct scatterlist_builder *builder,
> >  int scatterlist_builder_add_buffer(struct scatterlist_builder *builder,
> >                                  struct v4l2_buffer *b)
> >  {
> > +     int i;
> >       int ret;
> >
> > +     /* Fixup: plane length must be zero if userptr is NULL */
> > +     if (!V4L2_TYPE_IS_MULTIPLANAR(b->type) &&
> > +         b->memory == V4L2_MEMORY_USERPTR && b->m.userptr == 0)
> > +             b->length = 0;
> > +
> >       /* v4l2_buffer */
> >       ret = scatterlist_builder_add_data(builder, b, sizeof(*b));
> >       if (ret)
> >               return ret;
> >
> >       if (V4L2_TYPE_IS_MULTIPLANAR(b->type) && b->length > 0) {
> > +             /* Fixup: plane length must be zero if userptr is NULL */
> > +             if (b->memory == V4L2_MEMORY_USERPTR) {
> > +                     for (i = 0; i < b->length; i++) {
> > +                             struct v4l2_plane *plane = &b->m.planes[i];
> > +
> > +                             if (plane->m.userptr == 0)
> > +                                     plane->length = 0;
> > +                     }
> > +             }
> > +
> >               /* Array of v4l2_planes */
> >               ret = scatterlist_builder_add_data(builder, b->m.planes,
> >                                                  sizeof(struct v4l2_plane) *
> > @@ -368,6 +384,54 @@ int scatterlist_builder_add_buffer(struct scatterlist_builder *builder,
> >       return 0;
> >  }
> >
> > +/**
> > + * scatterlist_builder_add_buffer_userptr() - Add the payload of a ``USERPTR``
> > + *                                            &struct v4l2_buffer to the
> > + *                                            descriptor chain.
> > + * @builder: builder to use.
> > + * @b: &struct v4l2_buffer whose ``USERPTR`` payload we want to add.
> > + *
> > + * Add an array of &struct virtio_media_sg_entry pointing to a ``USERPTR``
> > + * buffer's contents. Does nothing if the buffer is not of type ``USERPTR``.
> > + * This is split out of scatterlist_builder_add_buffer() because we only want
> > + * to add these to the device-readable part of the descriptor chain.
> > + */
> > +int scatterlist_builder_add_buffer_userptr(struct scatterlist_builder *builder,
> > +                                        struct v4l2_buffer *b)
> > +{
> > +     int i;
> > +     int ret;
> > +
> > +     if (b->memory != V4L2_MEMORY_USERPTR)
> > +             return 0;
> > +
> > +     if (V4L2_TYPE_IS_MULTIPLANAR(b->type)) {
> > +             for (i = 0; i < b->length; i++) {
> > +                     struct v4l2_plane *plane = &b->m.planes[i];
> > +
> > +                     if (b->memory == V4L2_MEMORY_USERPTR &&
> > +                         plane->length > 0) {
> > +                             unsigned long uptr = plane->m.userptr;
> > +                             unsigned long len = plane->length;
> > +
> > +                             ret =
> > +                             scatterlist_builder_add_userptr(builder,
> > +                                                             uptr,
> > +                                                             len);
> > +                             if (ret)
> > +                                     return ret;
> > +                     }
> > +             }
> > +     } else if (b->length > 0) {
> > +             ret = scatterlist_builder_add_userptr(builder, b->m.userptr,
> > +                                                   b->length);
> > +             if (ret)
> > +                     return ret;
> > +     }
> > +
> > +     return 0;
> > +}
> > +
> >  /**
> >   * scatterlist_builder_retrieve_buffer() - Retrieve a &struct v4l2_buffer
> >   *                                         written by the device on the shadow
> > diff --git a/drivers/media/virtio/scatterlist_builder.h b/drivers/media/virtio/scatterlist_builder.h
> > index 47bfd7ae0..53d964a48 100644
> > --- a/drivers/media/virtio/scatterlist_builder.h
> > +++ b/drivers/media/virtio/scatterlist_builder.h
> > @@ -90,6 +90,9 @@ int scatterlist_builder_add_ioctl_resp(struct scatterlist_builder *builder,
> >  int scatterlist_builder_add_buffer(struct scatterlist_builder *builder,
> >                                  struct v4l2_buffer *buffer);
> >
> > +int scatterlist_builder_add_buffer_userptr(struct scatterlist_builder *builder,
> > +                                        struct v4l2_buffer *b);
> > +
> >  int scatterlist_builder_retrieve_buffer(struct scatterlist_builder *builder,
> >                                       size_t sg_index,
> >                                       struct v4l2_buffer *buffer,
> > diff --git a/drivers/media/virtio/virtio_media_driver.c b/drivers/media/virtio/virtio_media_driver.c
> > index c431c3eb2..b6f79593d 100644
> > --- a/drivers/media/virtio/virtio_media_driver.c
> > +++ b/drivers/media/virtio/virtio_media_driver.c
> > @@ -7,26 +7,29 @@
> >   */
> >
> >  #include <linux/bits.h>
> > +#include <linux/delay.h>
> >  #include <linux/device.h>
> >  #include <linux/dev_printk.h>
> > +#include <linux/mm.h>
> >  #include <linux/mutex.h>
> > +#include <linux/scatterlist.h>
> >  #include <linux/types.h>
> > +#include <linux/videodev2.h>
> > +#include <linux/vmalloc.h>
> > +#include <linux/wait.h>
> > +#include <linux/workqueue.h>
> >  #include <linux/module.h>
> > +#include <linux/moduleparam.h>
> >  #include <linux/virtio.h>
> >  #include <linux/virtio_config.h>
> >  #include <linux/virtio_ids.h>
> > -#include <linux/slab.h>
> > -#include <linux/scatterlist.h>
> > -#include <linux/vmalloc.h>
> > -#include <linux/workqueue.h>
> > -#include <linux/dma-mapping.h>
> > -#include <linux/poll.h>
> > -#include <linux/mm.h>
> >
> > +#include <media/frame_vector.h>
> >  #include <media/v4l2-dev.h>
> > -#include <media/v4l2-device.h>
> > -#include <media/v4l2-fh.h>
> >  #include <media/v4l2-event.h>
> > +#include <media/videobuf2-memops.h>
> > +#include <media/v4l2-device.h>
> > +#include <media/v4l2-ioctl.h>
> >
> >  #include "uapi/linux/virtio_media.h"
> >  #include "session.h"
> > @@ -40,6 +43,15 @@
> >  /* Bit mask for the VIRTIO_MEDIA_MMAP_FLAG_RW flag */
> >  #define VIRTIO_MEDIA_MMAP_FLAG_RW_MASK BIT(VIRTIO_MEDIA_MMAP_FLAG_RW)
> >
> > +/*
> > + * Whether USERPTR buffers are allowed.
> > + *
> > + * This is disabled by default as USERPTR buffers are dangerous, but the option
> > + * is left to enable them if desired.
> > + */
> > +bool virtio_media_allow_userptr;
> > +module_param_named(allow_userptr, virtio_media_allow_userptr, bool, 0660);
> > +
> >  /**
> >   * virtio_media_session_alloc() - Allocate a new session.
> >   * @vv: virtio-media device the session belongs to.
> > @@ -849,15 +861,11 @@ static int virtio_media_probe(struct virtio_device *virtio_dev)
> >                             VIRTIO_MEDIA_SHM_MMAP);
> >
> >       vd = &vv->video_dev;
> > +
> >       vd->v4l2_dev = &vv->v4l2_dev;
> >       vd->vfl_type = VFL_TYPE_VIDEO;
> >       vd->ioctl_ops = &virtio_media_ioctl_ops;
> >       vd->fops = &virtio_media_fops;
> > -     vd->release = video_device_release_empty;
> > -     strscpy(vd->name, "virtio-media", sizeof(vd->name));
> > -
> > -     video_set_drvdata(vd, vv);
> > -
> >       vd->device_caps = virtio_cread32(virtio_dev, 0);
> >       if (vd->device_caps & (V4L2_CAP_VIDEO_M2M | V4L2_CAP_VIDEO_M2M_MPLANE))
> >               vd->vfl_dir = VFL_DIR_M2M;
> > @@ -866,6 +874,10 @@ static int virtio_media_probe(struct virtio_device *virtio_dev)
> >               vd->vfl_dir = VFL_DIR_TX;
> >       else
> >               vd->vfl_dir = VFL_DIR_RX;
> > +     vd->release = video_device_release_empty;
> > +     strscpy(vd->name, "virtio-media", sizeof(vd->name));
> > +
> > +     video_set_drvdata(vd, vv);
> >
> >       ret = video_register_device(vd, virtio_cread32(virtio_dev, 4), 0);
> >       if (ret)
> > @@ -890,6 +902,7 @@ static int virtio_media_probe(struct virtio_device *virtio_dev)
> >       virtio_dev->config->del_vqs(virtio_dev);
> >  err_find_vqs:
> >       v4l2_device_unregister(&vv->v4l2_dev);
> > +
> >       return ret;
> >  }
> >
> > @@ -900,6 +913,7 @@ static void virtio_media_remove(struct virtio_device *virtio_dev)
> >
> >       cancel_work_sync(&vv->eventq_work);
> >       virtio_reset_device(virtio_dev);
> > +
> >       v4l2_device_unregister(&vv->v4l2_dev);
> >       virtio_dev->config->del_vqs(virtio_dev);
> >       video_unregister_device(&vv->video_dev);
> > diff --git a/drivers/media/virtio/virtio_media_ioctls.c b/drivers/media/virtio/virtio_media_ioctls.c
> > index f0b82b5ec..88465f239 100644
> > --- a/drivers/media/virtio/virtio_media_ioctls.c
> > +++ b/drivers/media/virtio/virtio_media_ioctls.c
> > @@ -273,6 +273,12 @@ static int virtio_media_send_buffer_ioctl(struct v4l2_fh *fh, u32 ioctl,
> >               return ret;
> >
> >       end_buf_sg = builder.cur_sg;
> > +
> > +     /* Payload of SHARED_PAGES buffers, if relevant */
> > +     ret = scatterlist_builder_add_buffer_userptr(&builder, b);
> > +     if (ret < 0)
> > +             return ret;
> > +
> >       num_cmd_sgs = builder.cur_sg;
> >
> >       /* Response descriptor */
> > @@ -719,7 +725,7 @@ static int virtio_media_reqbufs(struct file *file, void *fh,
> >       if (b->type > VIRTIO_MEDIA_LAST_QUEUE)
> >               return -EINVAL;
> >
> > -     if (b->memory == V4L2_MEMORY_USERPTR)
> > +     if (b->memory == V4L2_MEMORY_USERPTR && !virtio_media_allow_userptr)
> >               return -EINVAL;
> >
> >       ret = virtio_media_send_wr_ioctl(vfh, VIDIOC_REQBUFS, b, sizeof(*b),
> > @@ -752,7 +758,8 @@ static int virtio_media_reqbufs(struct file *file, void *fh,
> >       if (V4L2_TYPE_IS_MULTIPLANAR(b->type))
> >               session->uses_mplane = true;
> >
> > -     b->capabilities &= ~V4L2_BUF_CAP_SUPPORTS_USERPTR;
> > +     if (!virtio_media_allow_userptr)
> > +             b->capabilities &= ~V4L2_BUF_CAP_SUPPORTS_USERPTR;
> >
> >       /* We do not support DMABUF yet. */
> >       b->capabilities &= ~V4L2_BUF_CAP_SUPPORTS_DMABUF;
>
> --
> Regards,
>
> Laurent Pinchart