linux-kernel - Re: [PATCH v18 5/6] vfio: ABI for mdev display dma-buf operation

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Date:   Wed, 15 Nov 2017 21:11:42 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Zhenyu Wang <zhenyuw@...ux.intel.com>
Cc:     Tina Zhang <tina.zhang@...el.com>, kevin.tian@...el.com,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, joonas.lahtinen@...ux.intel.com,
        linux-kernel@...r.kernel.org, chris@...is-wilson.co.uk,
        kwankhede@...dia.com, zhiyuan.lv@...el.com, daniel@...ll.ch,
        hang.yuan@...el.com, intel-gvt-dev@...ts.freedesktop.org,
        zhi.a.wang@...el.com, kraxel@...hat.com
Subject: Re: [PATCH v18 5/6] vfio: ABI for mdev display dma-buf operation

On Thu, 16 Nov 2017 11:21:56 +0800
Zhenyu Wang <zhenyuw@...ux.intel.com> wrote:

> On 2017.11.15 11:48:42 -0700, Alex Williamson wrote:
> > On Wed, 15 Nov 2017 17:11:54 +0800
> > Tina Zhang <tina.zhang@...el.com> wrote:
> >   
> > > Add VFIO_DEVICE_QUERY_GFX_PLANE ioctl command to let user query and get
> > > a plane and its information. So far, two types of buffers are supported:
> > > buffers based on dma-buf and buffers based on region.
> > > 
> > > This ioctl can be invoked with:
> > > 1) Either DMABUF or REGION flag. Vendor driver returns a plane_info
> > > successfully only when the specific kind of buffer is supported.
> > > 2) Flag PROBE. And at the same time either DMABUF or REGION must be set,
> > > so that vendor driver returns success only when the specific kind of
> > > buffer is supported.
> > > 
> > > Add VFIO_DEVICE_GET_GFX_DMABUF ioctl command to let user get a specific
> > > dma-buf fd of an exposed MDEV buffer provided by dmabuf_id which was
> > > returned in VFIO_DEVICE_QUERY_GFX_PLANE ioctl command.
> > > 
> > > The life cycle of an exposed MDEV buffer is handled by userspace and
> > > tracked by kernel space. The returned dmabuf_id in struct vfio_device_
> > > query_gfx_plane can be a new id of a new exposed buffer or an old id of
> > > a re-exported buffer. Host user can check the value of dmabuf_id to see
> > > if it needs to create new resources according to the new exposed buffer
> > > or just re-use the existing resource related to the old buffer.
> > > 
> > > v18:
> > > - update comments for VFIO_DEVICE_GET_GFX_DMABUF. (Alex)
> > > 
> > > v17:
> > > - modify VFIO_DEVICE_GET_GFX_DMABUF interface. (Alex)
> > > 
> > > v16:
> > > - add x_hot and y_hot fields. (Gerd)
> > > - add comments for VFIO_DEVICE_GET_GFX_DMABUF. (Alex)
> > > - rebase to 4.14.0-rc6.
> > > 
> > > v15:
> > > - add a ioctl to get a dmabuf for a given dmabuf id. (Gerd)
> > > 
> > > v14:
> > > - add PROBE, DMABUF and REGION flags. (Alex)
> > > 
> > > v12:
> > > - add drm_format_mod back. (Gerd and Zhenyu)
> > > - add region_index. (Gerd)
> > > 
> > > v11:
> > > - rename plane_type to drm_plane_type. (Gerd)
> > > - move fields of vfio_device_query_gfx_plane to vfio_device_gfx_plane_info.
> > >   (Gerd)
> > > - remove drm_format_mod, start fields. (Daniel)
> > > - remove plane_id.
> > > 
> > > v10:
> > > - refine the ABI API VFIO_DEVICE_QUERY_GFX_PLANE. (Alex) (Gerd)
> > > 
> > > v3:
> > > - add a field gvt_plane_info in the drm_i915_gem_obj structure to save
> > >   the decoded plane information to avoid look up while need the plane
> > >   info. (Gerd)
> > > 
> > > Signed-off-by: Tina Zhang <tina.zhang@...el.com>
> > > Cc: Gerd Hoffmann <kraxel@...hat.com>
> > > Cc: Alex Williamson <alex.williamson@...hat.com>
> > > Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> > > ---
> > >  include/uapi/linux/vfio.h | 62 +++++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 62 insertions(+)
> > > 
> > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > > index ae46105..5c1cca2 100644
> > > --- a/include/uapi/linux/vfio.h
> > > +++ b/include/uapi/linux/vfio.h
> > > @@ -502,6 +502,68 @@ struct vfio_pci_hot_reset {
> > >  
> > >  #define VFIO_DEVICE_PCI_HOT_RESET	_IO(VFIO_TYPE, VFIO_BASE + 13)
> > >  
> > > +/**
> > > + * VFIO_DEVICE_QUERY_GFX_PLANE - _IOW(VFIO_TYPE, VFIO_BASE + 14,
> > > + *                                    struct vfio_device_query_gfx_plane)
> > > + *
> > > + * Set the drm_plane_type and flags, then retrieve the gfx plane info.
> > > + *
> > > + * flags supported:
> > > + * - VFIO_GFX_PLANE_TYPE_PROBE and VFIO_GFX_PLANE_TYPE_DMABUF are set
> > > + *   to ask if the mdev supports dma-buf. 0 on support, -EINVAL on no
> > > + *   support for dma-buf.
> > > + * - VFIO_GFX_PLANE_TYPE_PROBE and VFIO_GFX_PLANE_TYPE_REGION are set
> > > + *   to ask if the mdev supports region. 0 on support, -EINVAL on no
> > > + *   support for region.
> > > + * - VFIO_GFX_PLANE_TYPE_DMABUF or VFIO_GFX_PLANE_TYPE_REGION is set
> > > + *   with each call to query the plane info.
> > > + * - Others are invalid and return -EINVAL.
> > > + *
> > > + * Note:
> > > + * 1. Plane could be disabled by guest. In that case, success will be
> > > + *    returned with zero-initialized drm_format, size, width and height
> > > + *    fields.
> > > + * 2. x_hot/y_hot is set to 0xFFFFFFFF if no hotspot information available
> > > + *
> > > + * Return: 0 on success, -errno on other failure.
> > > + */
> > > +struct vfio_device_gfx_plane_info {
> > > +	__u32 argsz;
> > > +	__u32 flags;
> > > +#define VFIO_GFX_PLANE_TYPE_PROBE (1 << 0)
> > > +#define VFIO_GFX_PLANE_TYPE_DMABUF (1 << 1)
> > > +#define VFIO_GFX_PLANE_TYPE_REGION (1 << 2)
> > > +	/* in */
> > > +	__u32 drm_plane_type;	/* type of plane: DRM_PLANE_TYPE_* */
> > > +	/* out */
> > > +	__u32 drm_format;	/* drm format of plane */
> > > +	__u64 drm_format_mod;   /* tiled mode */
> > > +	__u32 width;	/* width of plane */
> > > +	__u32 height;	/* height of plane */
> > > +	__u32 stride;	/* stride of plane */
> > > +	__u32 size;	/* size of plane in bytes, align on page*/
> > > +	__u32 x_pos;	/* horizontal position of cursor plane */
> > > +	__u32 y_pos;	/* vertical position of cursor plane*/
> > > +	__u32 x_hot;    /* horizontal position of cursor hotspot */
> > > +	__u32 y_hot;    /* vertical position of cursor hotspot */
> > > +	union {
> > > +		__u32 region_index;	/* region index */
> > > +		__u32 dmabuf_id;	/* dma-buf id */
> > > +	};
> > > +};
> > > +
> > > +#define VFIO_DEVICE_QUERY_GFX_PLANE _IO(VFIO_TYPE, VFIO_BASE + 14)
> > > +
> > > +/**
> > > + * VFIO_DEVICE_GET_GFX_DMABUF - _IOW(VFIO_TYPE, VFIO_BASE + 15, __u32)
> > > + *
> > > + * Return a new dma-buf file descriptor for an exposed guest framebuffer
> > > + * described by the provided dmabuf_id. The dmabuf_id is returned from VFIO_
> > > + * DEVICE_QUERY_GFX_PLANE as a token of the exposed guest framebuffer.
> > > + */
> > > +
> > > +#define VFIO_DEVICE_GET_GFX_DMABUF _IO(VFIO_TYPE, VFIO_BASE + 15)
> > > +
> > >  /* -------- API for Type1 VFIO IOMMU -------- */
> > >  
> > >  /**  
> > 
> > Looks good to me.  Kirti, have you had a chance yet to verify this is
> > sufficient for your region-based approach?  It would be great to get
> > confirmation of that ASAP so we can get this in.  Thanks,
> >   
> 
> Alex, do you mind by merging this just through gvt tree? Or you would
> like to merge this then send pull request for us then we can apply left?

I'm fine with this going through the gvt tree, but I want some
confirmation from nvidia that this meets their needs as well before I
provide an ack.  Thanks,

Alex