On 2025/3/18 9:37, Gurchetan Singh wrote:
On Thu, Mar 6, 2025 at 2:52 AM Huang, Honglei1 <Honglei1.Huang@xxxxxxx
<mailto:Honglei1.Huang@xxxxxxx>> 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@xxxxxxx
<mailto:Honglei1.Huang@xxxxxxx>>
>>
>> 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.
I think userptr can be emulated by udmabuf if the sg list is from guest
user sapce and not moveable, amdkfd can operate dma-buf, and the userptr
feature can be achieved by partial functions of dma-buf as far as I can see.
But the udmabuf need managed by UMD, this will result in some
performance loss, and we are planning to implement virtio GPU userptr
using hmm_rang_fault, udmabuf solution may be completely different from
this one.
I saw the feature VIRTIO_GPU_BLOB_FLAG_CREATE_GUEST_HANDLE is used by
the crosvm in beta branch, but I can not find the kernel virtio gpu
part, how to access it? Maybe I can try or help.
Regards,
Honglei
