On 4 July 2018 at 18:00, Gerd Hoffmann <kraxel@xxxxxxxxxx> wrote: > On Wed, Jul 04, 2018 at 09:26:39AM +0200, Tomeu Vizoso wrote: >> On 07/04/2018 07:53 AM, Gerd Hoffmann wrote: >> > On Tue, Jul 03, 2018 at 10:37:57AM +0200, Daniel Vetter wrote: >> > > On Tue, Jul 03, 2018 at 09:53:58AM +0200, Gerd Hoffmann wrote: >> > > > A driver to let userspace turn memfd regions into dma-bufs. >> > > > >> > > > Use case: Allows qemu create dmabufs for the vga framebuffer or >> > > > virtio-gpu ressources. Then they can be passed around to display >> > > > those guest things on the host. To spice client for classic full >> > > > framebuffer display, and hopefully some day to wayland server for >> > > > seamless guest window display. >> > > > >> > > > qemu test branch: >> > > > https://git.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf >> > > > >> > > > Cc: David Airlie <airlied@xxxxxxxx> >> > > > Cc: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx> >> > > > Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> >> > > > Cc: Daniel Vetter <daniel@xxxxxxxx> >> > > > Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx> >> > > >> > > I think some ack for a 2nd use-case, like virtio-wl or whatever would be >> > > really cool. To give us some assurance that this is generically useful. >> > >> > Tomeu? Laurent? >> >> Sorry, but I think I will need some help to understand how this could help >> in the virtio-wl case [adding Zach Reizner to CC]. >> >> Any graphics buffers that are allocated with memfd will be shared with the >> compositor via wl_shm, without need for dmabufs. > > Within one machine, yes. Once virtualization is added to the mix things > become more complicated ... > > When using virtio-gpu the guest will allocate graphics buffers from > normal (guest) ram, then register these buffers (which are allowed to be > scattered) with the host as resource. > > qemu can use memfd to allocate guest ram. Now, with the help of > udmabuf, qemu can create a *host* dma-buf for the *guest* graphics > buffer. > > That dma-buf can be used by qemu internally (mmap it to get a linear > mapping of the resource, to avoid copying). It can be passed on to > spice-client, to display the guest framebuffer. > > And I think it could also be quite useful to pass guest wayland windows > to the host compositor, without mapping host-allocated buffers into the > guest, so we don't have do deal with the "find some address space for > the mapping" issue in the first place. There are more things needed to > complete this of course, but it's a building block ... There is a use case where I think we have to deal with the "find some address space" problem. For GL4.4 ARB_buffer_storage and Vulkan memory mangement there is the concept of coherent buffers between GPU and CPU. From the virgl point of view, we'd create a host buffer in GL, and then create a mapping from it on the host that we'd need to present in the guest userspace as a linear buffer. Just in case we think this can solve all our problems :-) Dave. -- To unsubscribe from this list: send the line "unsubscribe linux-kselftest" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
