The FSP That Wouldn't Die: A Blackwell GPU Reset Odyssey

Message Overview

In message <msg id=6314> of this opencode session, the assistant issues a single bash command to the remote server 10.1.2.6:

ssh root@10.1.2.6 'dmesg | grep -E "NVRM.*(failed|error|Error|Cannot|bad|WPR2)" | tail -10'

The output returns a damning set of kernel log entries:

[84521.041695] NVRM: GPU 0000:01:00.0: RmInitAdapter failed! (0x62:0xffff:2142)
[84521.042094] NVRM: GPU 0000:01:00.0: rm_init_adapter failed, device minor number 1
[84521.042356] NVRM: GPU2 gpuHandleSanityCheckRegReadError_GH100: Possible bad register read: addr: 0x110094,  regvalue: 0xbadf4100,  error code: Unknown SYS_PRI_ERROR_CODE
[84521.043147] NVRM: GPU2 RmInitAdapter: Cannot initialize GSP firmware RM
[84521.044265] NVRM: GPU 0000:61:00.0: RmInitAdapter failed! (0x62:0xffff:2142)

On its surface, this is a trivial diagnostic command — check the kernel log for NVIDIA driver errors. But in the arc of the conversation, this message represents a critical turning point: the moment the assistant confronts the grim reality that Blackwell GPUs possess a firmware-level security processor (FSP) that cannot be reset through any software mechanism, and that the entire IOMMU identity domain strategy — the central objective of the past several hours of work — is fundamentally incompatible with the hardware.

This article examines this single message in depth: why it was written, what assumptions led to this point, the knowledge it produced, and how it reshaped the trajectory of the session.

Context: The Quest for P2P DMA

To understand <msg id=6314>, one must understand the larger mission. The system under management is a Proxmox host with 8 NVIDIA RTX PRO 6000 Blackwell GPUs, split between an LXC container and a SEV-SNP (Secure Encrypted Virtualization - Secure Nested Paging) virtual machine. The assistant has been deploying large language models using SGLang, and a critical performance bottleneck has emerged: peer-to-peer (P2P) DMA between GPUs is broken.

Under SEV-SNP, the AMD IOMMU operates in a strict translation mode that intercepts all DMA transactions. When GPU A tries to directly access GPU B's memory (as NCCL requires for tensor-parallel communication), the IOMMU generates page faults because it doesn't recognize the peer GPU's PCI address space. The symptom is NCCL hangs and communication errors.

The standard fix for this on AMD systems is to set the IOMMU group type to identity — a mode that bypasses translation for that group's devices, allowing direct P2P DMA. The assistant has spent dozens of messages attempting to achieve this, cycling through an increasingly elaborate series of hardware reset techniques: driver unbind/rebind, PCI device removal and rescan, Secondary Bus Reset (SBR) on parent bridges, CXL bus resets, and even a full system reboot with modprobe hooks designed to set identity before the nvidia driver loads.

Why This Message Was Written

Message <msg id=6314> is written in direct response to the failure of the CXL bus reset approach attempted in <msg id=6312> and <msg id=6313>. The assistant had discovered that the Blackwell GPUs expose a cxl_bus reset method (alongside the standard flr and bus methods), and had successfully executed a CXL bus reset on all four NUMA0 GPUs:

0000:01:00.0: cxl_bus reset OK
0000:11:00.0: cxl_bus reset OK
0000:61:00.0: cxl_bus reset OK
0000:71:00.0: cxl_bus reset OK

This was a moment of optimism. CXL (Compute Express Link) bus reset operates at a lower hardware level than FLR (Function Level Reset) or standard PCI bus reset, and the assistant hoped it might clear the GPU's firmware state where other resets had failed. After the CXL reset, the assistant attempted to load the nvidia driver with identity domains already set — and got "No devices were found" from nvidia-smi.

Message <msg id=6314> is the diagnostic follow-up: the assistant needs to understand why the GPUs are invisible to nvidia despite the CXL reset succeeding. The specific grep pattern — NVRM.*(failed|error|Error|Cannot|bad|WPR2) — is carefully crafted to catch all known NVIDIA kernel module error signatures, including the WPR2 pattern that appeared in earlier FSP boot failures.

The message is thus motivated by a specific, urgent question: Did the CXL bus reset actually clear the FSP state, or are the GPUs still in the same corrupted condition?

The Output Knowledge Created

The output of this message is devastatingly clear. The error messages are identical to those seen in <msg id=6301> — the very first attempt to load nvidia after setting identity domains:

• RmInitAdapter failed! (0x62:0xffff:2142) — same error code
• gpuHandleSanityCheckRegReadError_GH100: Possible bad register read — same register address (0x110094), same bad value (0xbadf4100)
• Cannot initialize GSP firmware RM — same failure point The error code 0x62 is particularly significant. In NVIDIA's driver architecture, this corresponds to a GSP (GPU System Processor) firmware initialization failure. The 0xffff sub-code and 2142 detail code point to the FSP (Firmware Security Processor) boot sequence specifically — the FSP is a security-focused microcontroller embedded in Blackwell GPUs that handles firmware validation, cryptographic operations, and secure boot. It is designed to be tamper-resistant, which unfortunately means it is also resistant to software-initiated reset. The knowledge produced by this message is a negative result of profound importance: CXL bus reset, despite being the lowest-level software-initiated reset available, does not clear the Blackwell FSP state. The FSP's boot-time initialization — which includes setting up DMA mappings that the IOMMU must provide — has been corrupted, and no software mechanism can recover it. This message also implicitly confirms something even more troubling: the identity domain setting itself may be causing the FSP boot failure. The FSP appears to require specific DMA mappings that are set up by the kernel's DMA API during translation mode. When IOMMU is in identity mode, those mappings are never created, and the FSP's boot sequence fails with error 0x177 (as discovered in the subsequent chunk analysis).

Assumptions and Their Failure

Several assumptions underpin this message and the work that led to it:

Assumption 1: Software resets are sufficient. The assistant assumed that one of the available reset mechanisms (FLR, SBR, CXL bus) would be able to clear the GPU's firmware state. This assumption was rooted in decades of PCIe device management experience — on previous GPU generations (including Hopper/GH100), these resets worked reliably. Blackwell's FSP represents a fundamental architectural change that breaks this assumption.

Assumption 2: IOMMU group type is a per-group setting that can be changed at any time. The assistant assumed that writing identity to /sys/kernel/iommu_groups/$group/type would take effect immediately and be compatible with any driver. In reality, the IOMMU group type determines how DMA mappings are created during device initialization, and changing it after a device has already been initialized by a driver can leave the device in an inconsistent state.

Assumption 3: The nvidia driver can survive unbind/rebind. On previous GPU generations, unbinding and rebinding the nvidia driver was a standard troubleshooting technique. Blackwell's FSP architecture makes this destructive — once the driver unbinds, the FSP state is left in a limbo that no subsequent bind can recover.

Assumption 4: The identity domain approach is the only path to P2P DMA. The assistant had not yet fully explored the DmaRemapPeerMmio=1 nvidia driver parameter, which provides an alternative mechanism for P2P DMA that works within translation mode. This parameter was already enabled but producing incomplete IOMMU mappings.

Input Knowledge Required

To fully understand <msg id=6314>, the reader needs:

1. Understanding of IOMMU concepts: What DMA translation is, what identity domains do, and why P2P DMA requires either identity mode or special remapping.
2. Knowledge of NVIDIA GPU architecture: The distinction between GSP (GPU System Processor) and FSP (Firmware Security Processor), and how Blackwell's security architecture differs from previous generations.
3. Familiarity with PCIe reset mechanisms: FLR (Function Level Reset, PCIe capability), SBR (Secondary Bus Reset, bridge-level), and CXL bus reset (a newer mechanism for CXL-attached devices).
4. Context of SEV-SNP: AMD's Secure Encrypted Virtualization with Secure Nested Paging, which enables encrypted VM memory and strict IOMMU enforcement.
5. The session's history: The assistant has been working on this problem for dozens of messages, cycling through increasingly elaborate reset sequences. The reader needs to know that this is not the first failure but the culmination of a long chain of failed attempts.
6. NVIDIA error code semantics: Error 0x62:0xffff:2142 maps to GSP firmware initialization failure, and the 0xbadf4100 register value is a known "poison" pattern indicating a corrupted or uninitialized hardware state.

The Thinking Process Visible in This Message

The assistant's reasoning is visible in the structure of the diagnostic command itself. The grep pattern NVRM.*(failed|error|Error|Cannot|bad|WPR2) reveals what the assistant is looking for:

• failed and error/Error: Standard error indicators from the NVIDIA kernel module
• Cannot: Catches messages like "Cannot initialize GSP firmware RM"
• bad: Catches the "Possible bad register read" pattern with the 0xbadf4100 value
• WPR2: A specific error code seen in earlier FSP boot failures related to write-protected register access The assistant is not just checking "did it work?" — it's performing a differential diagnosis. It knows the exact error signatures from previous failures and is checking whether the CXL reset changed anything. The tail -10 limit is pragmatic: the NVIDIA driver can produce hundreds of log lines during initialization, and the critical errors are always in the last few lines. The thinking process also reveals a methodical, scientific approach. The assistant has been systematically testing each available reset mechanism and checking the results with the same diagnostic pattern. This consistency allows for clean comparisons across attempts.

The Broader Impact

Message <msg id=6314> is the moment the assistant accepts that per-group IOMMU identity domains are fundamentally incompatible with Blackwell GPUs. The CXL bus reset was the last software-level reset mechanism available, and its failure closes the door on this entire approach.

The subsequent messages (immediately following <msg id=6314>) show the assistant working through this realization. In <msg id=6315>, the assistant tries the "remove → SBR → rescan" sequence with nvidia loaded first (the only sequence that previously worked), and succeeds in restoring the GPUs — but they come back with DMA-FQ type, not identity. In <msg id=6319>, the assistant tests whether identity itself is the problem by setting DMA-FQ and trying to load nvidia — and finds that even DMA-FQ fails because the FSP is permanently corrupted from the earlier unbind attempts.

The final resolution comes when the assistant realizes that the only working sequence is: load nvidia module first, then rescan PCI (so nvidia probes fresh GPUs). This produces working GPUs with DMA-FQ type. The identity domain approach is abandoned, and the assistant pivots to alternative P2P strategies.

Conclusion

Message <msg id=6314> is a deceptively simple diagnostic command that carries enormous weight in the conversation. It is the moment of reckoning — when the assistant must accept that Blackwell's FSP architecture has defeated a standard Linux device management technique that has worked reliably for decades. The message produces critical negative knowledge: CXL bus reset does not clear FSP state, and the identity domain approach cannot work on this hardware.

The message also exemplifies the assistant's methodical approach to troubleshooting: formulate a hypothesis (CXL reset will clear FSP state), test it, and check with a consistent diagnostic pattern. When the output shows the same errors as before, the hypothesis is falsified, and the assistant must pivot.

For the broader session, this message marks the transition from the IOMMU identity domain quest to alternative P2P strategies (like DmaRemapPeerMmio=1), and ultimately to accepting the working configuration with MTP speculation as the primary optimization. The FSP that wouldn't die became the immovable object that forced a change in strategy.