P2P shows CNS on kernel 7.0.0-3-pve (Debian 13) with 2× RTX 3090

[svilendotorg]

Problem

P2P shows CNS (Chipset Not Supported) on Linux kernel 7.0.0-3-pve (Proxmox VE / Debian 13) even with the patched P2P modules. The same patch works perfectly on 6.17.13-6-pve on identical hardware.

Hardware

Component	Detail
CPU	AMD EPYC 7443P (24C/48T, PCIe 4.0)
Mobo	Supermicro MBD-H12SSL-CT (SP3, ATX)
GPU #1	RTX 3090 @ PCIe x16 (01:00.0, Gen4 x16)
GPU #2	RTX 3090 @ PCIe x16 (c1:00.0, Gen4 x16)
OS	Proxmox VE (Debian 13)

Driver & Kernel

Item	Value
Driver	595.58.03
CUDA	13.2.1
Branch	595.58.03-p2p
Working kernel	6.17.13-6-pve ✅ (P2P OK)
Broken kernel	7.0.0-3-pve ❌ (P2P CNS)

Reproduction

# Install from the p2p branch
git clone -b 595.58.03-p2p --single-branch https://github.com/aikitoria/open-gpu-kernel-modules
cd open-gpu-kernel-modules && ./install.sh

# Check P2P
nvidia-smi topo -p2p r

On 6.17.13-6-pve → P2P reads/writes show OK.
On 7.0.0-3-pve → P2P reads/writes show CNS.

Additional Notes

• Kernel 7.0.0 also ships nova_core (NVIDIA's open-source Rust GPU driver) that auto-binds to one of the two GPUs, causing 0xbadf5720 PCIe register errors. This was worked around with modprobe blacklisting (blacklist nova + blacklist nova_core), but the P2P CNS issue persists even after that is fixed.
• Both GPUs are on independent PCIe lanes (GPP0 and GPP3) — no shared switch.
• Full system details available on request.

Expected Behavior

P2P should show OK on 7.0.0-3-pve the same as on 6.17.13-6-pve.

[aikitoria]

I'll be able to investigate this once Debian testing ships kernel 7.0.0

[frenzybiscuit]

I can confirm this issue on Ubuntu 26.04.

[frenzybiscuit]

Let me know if you need a test setup for 4x3090. I would be more then happy to give you SSH access to the node so you can work on this driver.

[aikitoria]

I can't reproduce the issue locally, just updated to kernel 7 and it works completely fine on my 8x 5090 setup after rebuilding the driver.

[frenzybiscuit]

Happens to me on Ubuntu 26.04.

I installed Proxmox with 6.17.2-1-pve and P2P works.

[aikitoria]

I don't use proxmox or any kind of hypervisor on my local server. Perhaps that is the difference.

[frenzybiscuit]

I don't use proxmox or any kind of hypervisor on my local server. Perhaps that is the difference.

Ubuntu 26.04 is just the base install; no hybervisor.

I'm just saying kernel 6.17.2-1 works for me whereas the Ubuntu 26.04 kernel did not.