DisplayOnly Driver and Memory Reporting

NTDEV
1

Hello,

I am maintaining a display only driver (DOD) responsible for providing certain graphic services from the host into virtual machine(s). The driver is based on Microsoft’s KMDOD sample. My question is: is it possible to report “GPU RAM/VRAM” used by the adapter represented by the driver (so you can see the values in the display adapter settings windows)?

My (current) understanting of this problem is that Windows reports GPU RAM and VRAM based on the information provided by the driver through the DxgkDdiQueryAdapterInfo callback. The driver reports this information by specifying memory segments used by GPU through DXGKQAITYPE_QUERYSEGMENT (or DXGKQAITYPE_QUERYSEGMENT3) type. This seems to work fine for the Display Miniport drivers, however, not for DODs – I never get DxgkDdiQueryAdapterInfo called for these information types, thus, nothing can be reported. So, it seems that DODs are abstracted from this thing by WDDM/miniport driver.

Does anyone have more experience with this? Basically, I just need to report the GRU memory and VRAM sizes, that’s all.

Thank you!

2

From discussions with the owners of the DirectX Kernel (regarding different things, but still KMDOD-related), I don’t believe this is possible with the KMDOD interface. The whole point of the KMDOD setup is that the device in question is not and can not be considered a full GPU by the OS, and therefor a vast majority of the “GPU” aspects that a full WDDM driver provides are skipped entirely. For example, there is no requirement that the hardware being driven by a KMDOD even have its own memory - as long as it can perform a DMA, it could be configured to scan out the rendered image directly from the location provided by the DXGKARG_PRESENT_DISPLAYONLY structure in its DdiPresentDisplayOnly callback.

The KMDOD interface works very well for the very limited use case it supports, but for everything else… you need a full WDDM stack.