When the GPUs Wouldn't Wake Up: A Blackwell GSP Firmware Crisis

Introduction

In the high-stakes world of large-scale ML inference deployment, the difference between a successful optimization and a catastrophic system failure can be a single kernel parameter. Message 6268 of this opencode session captures one such moment: the instant when a carefully planned GPU P2P DMA restoration attempt through per-group IOMMU identity domains went spectacularly wrong, leaving four NVIDIA RTX PRO 6000 Blackwell GPUs in an unrecoverable state. This message is the pivot point — the moment where the assistant transitions from executing a planned optimization to diagnosing a system-level crisis.

The Context: A Quest for P2P DMA

To understand the gravity of this message, we must first understand what led to it. The session had been working on deploying large language models (specifically Qwen3.5-122B-A10B BF16) across 4 NVIDIA RTX PRO 6000 Blackwell GPUs with tensor parallelism (TP=4). The system was running under a Proxmox host with amd_iommu=on for SEV-SNP virtual machine support, which meant GPU P2P DMA was broken — NCCL's peer-to-peer transfers were faulting on the IOMMU, forcing the deployment to use NCCL_P2P_DISABLE=1 and suffer the performance penalty of staging all-reduce operations through system memory.

The assistant had researched a promising solution: Linux kernels since v5.11 support per-IOMMU-group domain type switching via the sysfs interface at /sys/kernel/iommu_groups/<grp_id>/type. By setting specific GPU groups to identity mode (which bypasses IOMMU translation for those devices) while keeping other groups (like the VFIO GPUs assigned to the SEV-SNP VM) in DMA-FQ translation mode, the system could theoretically have both working P2P DMA for the inference GPUs and full SEV-SNP protection for the VM. The plan was elegant, well-researched, and had been explicitly approved by the user.

The Execution and the Failure

The assistant had executed the plan methodically. It stopped the SGLang service ([msg 6257]), unbound all 4 GPUs from the nvidia driver ([msg 6263]), set the IOMMU group types to identity ([msg 6263]), and rebinded the nvidia driver ([msg 6265]). On paper, this should have worked. The kernel documentation supported it, the hardware was compatible, and the sequence was textbook.

But message 6268 reveals the brutal reality: it didn't work. Not even close.

The assistant opens the message with a stark summary:

All 4 GPUs failed to initialize — RmInitAdapter failed! (0x62:0xffff:2142) and kfspSendBootCommands_HAL failures. The GPUs are in a bad state after the unbind/rebind. This is likely because the GSP firmware context was lost during unbind and the GPU needs a proper PCI reset before rebinding.

This single sentence packs an enormous amount of diagnostic insight. The assistant correctly identifies that the issue is not a simple driver loading failure but a firmware-level problem. The RmInitAdapter error (0x62) is NVIDIA's resource manager initialization failure, and the kfspSendBootCommands_HAL error points to the GPU System Processor (GSP) — a dedicated microcontroller embedded in modern NVIDIA GPUs that handles boot, power management, and security functions.

The GSP Firmware Problem: A Deeper Look

The GSP (GPU System Processor) is a relatively recent addition to NVIDIA's GPU architecture, introduced with the Turing generation and significantly expanded in Ampere and subsequent architectures. On Blackwell GPUs (the RTX PRO 6000 series), the GSP handles critical boot-time initialization, including loading firmware into Write Protected Regions (WPRs) of the GPU's internal memory. When the assistant unbound the nvidia driver from the GPUs, the GSP firmware context — including the WPR2 region — was left in a "locked" state. When the driver was rebinded, it tried to reinitialize the GSP and found WPR2 already active, causing it to abort with the error _kgspBootGspRm: unexpected WPR2 already up, cannot proceed with booting GSP.

This is a fundamental hardware-software interaction that the assistant's plan had not accounted for. The assumption was that unbinding and rebinding the nvidia driver would be a clean operation — that the driver would properly tear down the GPU state and reinitialize it fresh. But the GSP firmware maintains persistent state across driver unbind operations. The WPR2 region is locked by the GSP during the first boot and is not released when the driver unloads. Only a full PCI bus reset — either a Function Level Reset (FLR) or a Secondary Bus Reset (SBR) — can clear this state.

The Recovery Attempt: PCI Remove and Rescan

Faced with four bricked GPUs, the assistant's response is immediate and pragmatic. It doesn't panic or ask for help — it diagnoses and acts. The recovery strategy is a PCI remove + rescan cycle:

echo 1 > /sys/bus/pci/devices/$gpu/remove
...
echo 1 > /sys/bus/pci/rescan

This is the standard Linux kernel mechanism for hot-unplugging and re-enumerating PCI devices. The remove sysfs file triggers a full teardown of the PCI device, releasing all kernel resources and resetting the PCI configuration space. The rescan triggers the PCI subsystem to re-enumerate all buses, re-discover devices, and re-probe drivers.

The assistant's reasoning is sound: if the GSP state is stuck because the driver didn't properly clean up, then removing the device from the PCI bus entirely and rediscovering it should force a fresh initialization from power-on state. This is equivalent to a virtual hot-unplug and hot-plug of the GPU.

What the PCI Rescan Revealed

The output of the PCI rescan attempt is revealing:

=== Checking GPU states after rescan ===
  0000:01:00.0: exists, driver=nvidia, group=28, type=DMA-FQ
  0000:11:00.0: exists, driver=nvidia, group=61, type=DMA-FQ
  0000:61:00.0: exists, driver=nvidia, group=42, type=DMA-FQ
  0000:71:00.0: exists, driver=nvidia, group=10, type=DMA-FQ

The GPUs reappeared, the nvidia driver auto-probed them, but crucially, the IOMMU group types had reverted to DMA-FQ. Worse, the group numbers had changed — GPU 0000:01:00.0 was now in group 28 instead of its original group 42, and 0000:61:00.0 was now in group 42 instead of group 28. This group reassignment is a known behavior: when PCI devices are removed and rescanned, the kernel may assign them to different IOMMU groups based on the order of discovery and the underlying AMD-Vi IOMMU hardware topology. The identity domain setting, being a runtime sysfs configuration, did not survive the device removal.

But the most critical discovery — one that would only fully surface in subsequent messages — is that even the PCI remove + rescan did not clear the GSP state. The GPUs reappeared, the driver loaded, but the RmInitAdapter errors persisted. The WPR2 lock survived the PCI remove cycle, meaning that a simple software-level device removal was insufficient to reset the GSP firmware. This would force the assistant to escalate to progressively more aggressive reset techniques: FLR (Function Level Reset), bus-level reset, and ultimately Secondary Bus Reset via the parent PCIe bridge's control register.

Assumptions and Their Consequences

Message 6268 reveals several assumptions that turned out to be incorrect:

Assumption 1: Unbinding and rebinding the nvidia driver is a clean operation. The assistant assumed that the nvidia driver would properly tear down GPU state during unbind and reinitialize from scratch during rebind. In reality, the GSP firmware maintains persistent state (WPR2) that survives driver unbind, and the driver's reinitialization code does not handle the "WPR2 already up" case gracefully.

Assumption 2: The IOMMU identity domain setting would persist across driver rebind. The assistant had successfully set the group types to identity while the GPUs were unbound. The assumption was that when the nvidia driver rebinded, it would see the identity domain and work correctly. But the driver's initialization failed at the GSP level before it ever got to use the IOMMU configuration.

Assumption 3: The PCI remove/rescan would fully reset the GPU state. This is a reasonable assumption — PCI device removal should trigger a complete teardown. But the GSP firmware's WPR2 region is mapped to GPU-internal memory that is not cleared by a PCI configuration space reset. The GSP maintains its state across PCI remove/rescan because the GPU's internal power rails remain active (the GPU is not physically power-cycled).

Assumption 4: The nvidia driver would not auto-probe during rescan. The assistant may have hoped that after the rescan, the GPUs would appear without a driver bound, allowing a clean identity-domain-then-bind sequence. But the nvidia driver is registered as a match for the GPU's PCI vendor/device ID (10de:2bb5), so the kernel's driver core automatically binds it during device discovery.

The Knowledge Created

Despite being a failure, message 6268 generates significant knowledge:

  1. Blackwell GSP firmware behavior: The GSP on RTX PRO 6000 Blackwell GPUs maintains persistent WPR2 state across driver unbind/rebind cycles. This is a critical piece of hardware knowledge that affects any GPU hot-swap or driver reload scenario.
  2. PCI remove/rescan limitations: Software-level PCI device removal does not reset the GPU's internal firmware state. The GSP requires a hardware-level reset (FLR, SBR, or power cycle) to clear its locked regions.
  3. IOMMU group reassignment: PCI device removal and rescan can cause IOMMU group numbers to change, as the kernel reassigns devices to groups based on the AMD-Vi hardware topology at discovery time.
  4. Error signature for GSP lock: The specific error pattern — RmInitAdapter failed (0x62:0xffff:2142) combined with _kgspBootGspRm: unexpected WPR2 already up — is a diagnostic fingerprint for a GPU that has been unbound and rebinded without a proper hardware reset.

The Thinking Process

What makes message 6268 particularly interesting is the thinking process it reveals. The assistant does not simply report the error and give up. It immediately formulates a hypothesis ("GSP firmware context was lost during unbind"), proposes a recovery strategy ("GPU needs a proper PCI reset before rebinding"), and executes that strategy with a carefully constructed bash script.

The script itself shows thoughtful design: it unbinds all GPUs first (to avoid conflicts), then removes them from the PCI bus one at a time, waits for the removal to complete, rescans the bus, and then checks the state of each GPU. The error handling is minimal but functional — the set -e ensures the script stops on any failure, and the || echo fallbacks provide visibility into what succeeded and what didn't.

The assistant also demonstrates good diagnostic practice by checking the state after the rescan rather than assuming success. It prints driver, group, and type information for each GPU, giving a complete picture of the post-rescan state.

The Broader Significance

Message 6268 is a case study in the gap between theory and practice in systems engineering. The per-group IOMMU identity domain approach was theoretically sound, well-documented, and had been successfully used by others. But it failed because of an undocumented hardware behavior — the GSP firmware's persistent WPR2 state — that no amount of kernel documentation could have predicted.

This is the reality of working with cutting-edge hardware like Blackwell GPUs. The software interfaces (sysfs, PCI hotplug, IOMMU groups) are mature and well-defined, but the hardware behaviors (GSP firmware state machines, WPR locking, reset domain boundaries) are often opaque and only discovered through painful experimentation. The assistant's response — methodical diagnosis, hypothesis formation, and systematic recovery attempts — is exactly the right approach to such situations.

The message also highlights a broader truth about ML infrastructure: the most impactful optimizations often involve the deepest hardware-software interactions. P2P DMA, IOMMU configuration, GPU firmware, PCI bus topology — these are not topics that come up in everyday ML engineering, but they can make or break the performance of a large-scale deployment. The assistant's willingness to dive into this territory, and its ability to recover when things go wrong, is a testament to the depth of systems knowledge required for this work.

Conclusion

Message 6268 is a turning point in the session. The elegant P2P restoration plan has failed, four GPUs are in a bad state, and the assistant must now escalate to more aggressive recovery techniques. But the message is also a demonstration of resilience under pressure — the ability to diagnose a complex hardware failure, formulate a recovery strategy, and execute it without hesitation. The PCI remove/rescan attempt may not have fully resolved the issue (that would require SBR, as shown in subsequent messages), but it was the right first step in a systematic recovery process. And the knowledge gained — about Blackwell GSP behavior, PCI reset limitations, and IOMMU group dynamics — would prove invaluable in the sessions to come.