Re: [PATCH v1 1/7] virtio-gpu api: add blob userptr resource

[Gurchetan Singh <gurchetansingh@chromium.org>]

[-- Attachment #1: Type: text/plain, Size: 1774 bytes --]

On Thu, Mar 6, 2025 at 2:52 AM Huang, Honglei1 <Honglei1.Huang@amd.com>
wrote:

>
> On 2025/3/1 5:21, Demi Marie Obenour wrote:
> > On 2/28/25 12:36 AM, Honglei Huang wrote:
> >> From: Honglei Huang <Honglei1.Huang@amd.com>
> >>
> >> Add a new resource for blob resource, called userptr, used for let
> >> host access guest user space memory, to acquire buffer based userptr
> >> feature in virtio GPU.
> >>
> >> - The capset VIRTIO_GPU_CAPSET_HSAKMT used for context init,
> >> in this series patches only HSAKMT context can use the userptr
> >> feature. HSAKMT is a GPU compute library in HSA stack, like
> >> the role libdrm in mesa stack.
> >
> > Userptr should not be limited to HSMKMT contexts.  Userptr can
> > accelerate shm buffers by avoiding a copy from guest to host, and
> > it can be implemented using grant tables on Xen.
>
> Yes, I totally agree userptr can accelerate shm buffers, but I currently
> don't know if there are any other projects working on similar features,
> or if maintainers have any opinions or better ways to implement them, so
> I temporarily limit this feature to HSAKMT context only.
>
> I am waiting for everyone's opinions, please provide your thoughts.
>

I wonder if you can emulate userptr using udmabuf on the host-side?

Essentially for the guest, it'll be a malloc'ed memory, which means a guest
sg list.  We can convert the guest sg-list to udmabuf using well-known
mechanisms on the host side.  I hope amdkfd can operate on dma-bufs too?

I do such a feature that would have a more generic utility outside of
HSAKMT contexts and not rely on Xen-specific grant tables  ...
checkout VIRTIO_GPU_BLOB_FLAG_CREATE_GUEST_HANDLE in crosvm for an
example.




>
> Regards,
> Honglei
>

[-- Attachment #2: Type: text/html, Size: 2552 bytes --]