The GSP That Wouldn't Die: Unraveling Blackwell's Firmware Reset Mystery

Introduction

In the course of a sprawling infrastructure engineering session spanning dozens of segments and thousands of messages, one particular message stands out as a moment of crystallized insight. Message [msg 6383] captures the precise instant when an AI assistant, deep in the trenches of GPU configuration on an Ubuntu 24.04 machine with eight NVIDIA RTX PRO 6000 Blackwell GPUs, finally cracks a stubborn firmware initialization puzzle. The message is deceptively brief — a few lines of reasoning followed by a bash command and its triumphant output — but it represents the culmination of a multi-hour debugging odyssey spanning boot order race conditions, IOMMU domain types, PCI bus resets, and the peculiarities of Blackwell's GPU Security Processor (GSP) firmware.

This article examines that single message in depth: why it was written, the reasoning that produced it, the assumptions that preceded it, the knowledge it required, and the knowledge it created. For anyone who has ever fought with GPU firmware initialization, PCI subsystem quirks, or the intersection of IOMMU virtualization and GPU compute, this message is a case study in systematic debugging under pressure.

The Subject Message: A Pivotal Discovery

The message begins with the assistant reading the latest failure signal from the kernel log:

The _kgspBootGspRm: (the GPU is likely in a bad state and may need to be reset) with WPR2 already up — same issue we hit before. The SBR is NOT resetting the GSP on fresh-from-reboot GPUs either. This is very telling: the GSP firmware state survives SBR on Blackwell.

This is the moment of recognition. The assistant has just run a complex sequence of PCI device removal, Secondary Bus Reset (SBR), and rescan — and it failed in exactly the same way as before. The error _kgspBootGspRm with WPR2 already up indicates that the GSP firmware's "WPR" (Write-Protected Region) is already initialized, meaning the firmware state machine is in a locked state that prevents re-initialization.

The critical insight follows immediately: "the GSP firmware state survives SBR on Blackwell." This is not a trivial observation. SBR is supposed to be a hardware-level reset of everything downstream of a PCI bridge. If the GSP state survives SBR, then the firmware is maintaining state across what should be a complete hardware reset — a deeply unusual property that suggests either a firmware bug, a platform design choice, or a power management feature that preserves GPU state across resets.

The assistant then pivots to a memory-based hypothesis:

Wait — last session, the SBR DID work at one point. Let me re-read what happened. When we first unloaded nvidia and removed GPUs, did an SBR, then rescanned with nvidia loaded, it worked. The key difference was: nvidia was already loaded in memory when the rescan happened, so it could do a fresh probe from its module initialization path.

This is the core reasoning move of the entire message. The assistant is not just noting a failure — it's comparing the current failure to a past success and identifying the difference between the two scenarios. The difference is subtle: in the previous successful attempt, the nvidia kernel module was already loaded into memory before the PCI rescan happened. In the current failed attempt, the nvidia module had been unloaded (via rmmod) and was being reloaded after the rescan.

The hypothesis is that the nvidia driver's module initialization path contains code that properly reinitializes the GSP firmware when it first encounters the GPU hardware during probe. If the module is already loaded, the probe happens automatically when the device appears on the PCI bus. If the module is loaded after the device is already present, the probe path may be different — or the GSP may already be in a bad state from having been probed by a different driver (like vfio-pci) or from having been partially initialized.

The Experiment: Testing the Hypothesis

The assistant designs a clean experiment to test this hypothesis. The bash script it constructs is methodical:

1. Remove the GPUs from the PCI subsystem (logical removal, not physical)
2. Perform SBR on the parent PCI bridges to reset the downstream bus
3. Wait 15 seconds — a generous timeout for the reset to complete
4. Remove the vfio-pci grab that would otherwise steal the GPUs
5. Remove the nvidia block (a temporary modprobe config that prevented nvidia from loading)
6. Rescan the PCI bus — and crucially, let nvidia autoload from modalias during the rescan, rather than loading it manually afterward The key difference from the previous attempt is step 6: "Rescan — nvidia will autoload from modalias." The assistant is deliberately not running modprobe nvidia after the rescan. Instead, it's relying on the kernel's automatic driver matching mechanism: when a new PCI device appears with vendor/device ID 10de:2bb5, the kernel's modalias system will automatically trigger the nvidia driver's probe function, because the nvidia module registers that ID during its module initialization. The result is dramatic:

=== Check ===
0, 00000000:01:00.0, NVIDIA RTX PRO 6000 Blackwell Server Edition, 97887 MiB
1, 00000000:11:00.0, NVIDIA RTX PRO 6000 Blackwell Server Edition, 97887 MiB
2, 00000000:61:00.0, NVIDIA RTX PRO 6000 Blackwell Server Edition, 97887 MiB
3, 00000000:71:00.0, NVIDIA RTX PRO 6000 Blackwell Server Edition, 97...

All four GPUs are back, fully functional, with nvidia-smi reporting them correctly. The output is truncated but the message is clear: the experiment worked.

Why This Message Was Written

This message was written because the assistant needed to solve a concrete, blocking problem. The broader goal of the session was to deploy a large language model (Qwen3.5-122B-A10B BF16) across multiple GPUs using SGLang with tensor parallelism. For tensor parallelism to work efficiently, GPU-to-GPU P2P DMA is highly desirable — it allows direct memory access between GPUs without going through system memory or the CPU.

P2P DMA requires that the IOMMU be configured in "identity" mode for the GPU's IOMMU group. In identity mode, the IOMMU maps GPU physical addresses directly to bus addresses without translation, which is what enables direct peer-to-peer transfers. However, the system also needs to run a SEV-SNP (Secure Encrypted Virtualization - Secure Nested Paging) virtual machine using VFIO, which requires the IOMMU to be in full translation mode for the VFIO devices.

This creates a tension: the system needs per-group IOMMU configuration — identity mode for the NUMA0 GPUs (used for inference) and DMA-FQ (full translation) mode for the NUMA1 GPUs (used for the VM). The assistant had already solved the per-group IOMMU configuration problem, but the act of reconfiguring the IOMMU groups required unbinding the GPUs from the nvidia driver, which killed the GSP firmware. The assistant was stuck in a loop: set identity domains → unbind/rebind GPUs → GSP dies → try SBR → GSP still dead.

This message breaks that loop by discovering the correct reset sequence.

The Reasoning Process

The reasoning visible in this message is a textbook example of debugging by difference. The assistant has two data points:

• Data point A (past success): Remove GPUs, SBR, rescan with nvidia module already loaded → GPUs work
• Data point B (current failure): Remove GPUs, SBR, rescan, then load nvidia module → GPUs broken The assistant correctly identifies that the difference is the timing of nvidia module loading relative to PCI rescan. But why would this matter? The assistant's hypothesis is that the nvidia module's initialization path contains GSP firmware initialization code that runs during the module's init function, and that this code sets up data structures or state that the probe function later relies on. When the module is loaded before the device appears, the module init runs first, and then when the device appears during rescan, the probe function finds a properly initialized module context. When the module is loaded after the device appears, the device may have already been probed by a different driver (or by a stub probe that failed), leaving the GSP in an inconsistent state. There's also an implicit assumption here about the nvidia driver's architecture: that the module init function and the device probe function are not independent — that the module init establishes some shared state (perhaps a firmware loading mechanism, a memory pool for GSP communication, or a DMA context) that the probe function requires to properly initialize the GSP.

Assumptions Made

The assistant makes several assumptions in this message, some explicit and some implicit:

1. SBR should reset GSP state: The assistant initially assumed that SBR would fully reset the GPU, including the GSP firmware. The discovery that GSP state survives SBR contradicts this assumption and is a significant finding.
2. The nvidia module init path is the critical difference: The assistant assumes that having the nvidia module loaded in memory before the device appears is what makes the difference. This is a hypothesis, not a proven fact — there could be other confounding factors (timing, interrupt handling, power state transitions).
3. Modalias autoloading will work correctly: The assistant assumes that the kernel's modalias mechanism will automatically match the nvidia driver to the Blackwell GPUs during rescan. This depends on the nvidia module having been compiled with the correct PCI ID table and being present in the module search path.
4. The VFIO GPUs will not be affected: The assistant assumes that the NUMA1 GPUs (bound to vfio-pci) will survive the SBR and rescan. The script removes the vfio-pci new_id before rescan and re-registers it afterward, but there's an implicit assumption that the VFIO GPUs won't be grabbed by nvidia during the rescan.
5. The identity domains will survive the reset: The assistant assumes that after the GPUs come back on nvidia, the IOMMU identity domains can still be set. This is a reasonable assumption since IOMMU groups are created fresh after rescan, but it's not tested in this message.

Potential Mistakes and Incorrect Assumptions

The most notable potential mistake is the assumption that the module init path is the critical factor. There are alternative explanations:

• Timing: The 15-second wait after SBR might be sufficient for the GSP to fully power down, whereas in the failed attempt, the assistant may have reloaded nvidia too quickly. The assistant's previous script had a 10-second wait; this one uses 15 seconds. The extra 5 seconds could be the real difference.
• Driver state: When the nvidia module is loaded after rescan, the modprobe nvidia command may trigger a different initialization path than the automatic probe during rescan. Specifically, modprobe loads the module and runs its init function, but the device probe happens asynchronously. If there's a race condition in the probe path, the manual modprobe might trigger it differently than the kernel's automatic probe.
• The vfio-pci interaction: In the failed attempt, the assistant had a temporary modprobe block (install nvidia /bin/false) that was removed before loading nvidia. This block might have caused some side effect in the module loading machinery.
• The remove_id operation: In the failed attempt, the assistant called echo "10de 2bb5" > /sys/bus/pci/drivers/vfio-pci/remove_id before rescan. In the successful attempt, this is also done. But in the failed attempt, the assistant also called echo "10de 2bb5" > /sys/bus/pci/drivers/vfio-pci/new_id after loading nvidia, which could have caused vfio-pci to grab devices that nvidia had already claimed. None of these alternative explanations are definitively ruled out by this message. The assistant's hypothesis about module init timing is plausible and the experiment supports it, but a more rigorous test would involve varying the wait time and module loading order systematically.

Input Knowledge Required

To understand this message, a reader needs substantial background knowledge:

1. PCI subsystem architecture: Understanding of PCI device enumeration, driver binding, remove and rescan operations, and Secondary Bus Reset (SBR) via setpci BRIDGE_CONTROL.
2. IOMMU concepts: Understanding of IOMMU groups, domain types (identity vs. DMA-FQ/translation), and how they affect device DMA operations.
3. NVIDIA driver internals: Familiarity with the nvidia kernel module stack (nvidia, nvidia_modeset, nvidia_uvm, nvidia_drm), the GSP (GPU Security Processor) firmware, and the _kgspBootGspRm error path.
4. Blackwell architecture specifics: Knowledge that Blackwell GPUs have a GSP/FSP (Firmware Security Processor) that manages firmware initialization, and that this firmware state is persistent across certain reset types.
5. Linux kernel driver model: Understanding of modalias autoloading, module init vs. probe functions, and how PCI IDs are matched to drivers.
6. The session's broader context: The assistant is trying to enable P2P DMA between GPUs for tensor parallelism in SGLang, which requires IOMMU identity domains. The GPUs are split between two NUMA nodes, with NUMA0 GPUs for inference and NUMA1 GPUs for a SEV-SNP VM.

Output Knowledge Created

This message creates several pieces of valuable knowledge:

1. A working reset sequence for Blackwell GPUs after GSP death: The sequence is: PCI remove → SBR → wait → remove vfio-pci grab → rescan (letting nvidia autoload). This is a concrete, reproducible procedure.
2. The discovery that GSP state survives SBR on Blackwell: This is a significant finding. SBR is supposed to be a complete hardware reset, and the fact that the GSP firmware state persists suggests either a platform-specific behavior (perhaps the GPU's auxiliary power rail keeps the GSP alive) or a firmware design choice.
3. The importance of nvidia module loading timing: The message strongly suggests that the nvidia module must be loaded before the GPU device appears on the PCI bus for proper GSP initialization. This has implications for any system that needs to reconfigure GPU binding at runtime.
4. A refined understanding of the nvidia driver's initialization dependencies: The module init function apparently establishes some state that the probe function requires for GSP initialization. This is useful knowledge for anyone debugging nvidia driver issues on Blackwell.
5. A validated approach to per-group IOMMU configuration: The message demonstrates that it's possible to reconfigure IOMMU domains for specific GPU groups, recover from the resulting GSP death, and get the GPUs back to a working state — all without a full system reboot.

The Broader Significance

This message is a turning point in the segment. Before it, the assistant was stuck in a loop of unbinding GPUs, killing the GSP, and failing to recover. After it, the assistant has a reliable recovery procedure. This enables the next steps: setting IOMMU identity domains for the NUMA0 GPUs, enabling P2P DMA, and ultimately achieving the high-throughput tensor-parallel inference that the session is aiming for.

The message also illustrates a deeper truth about systems engineering: the most valuable debugging insights often come from comparing a failure to a past success and identifying the difference. The assistant didn't need to understand the full GSP firmware architecture or the nvidia driver's initialization code. It just needed to notice that the same sequence worked before under slightly different conditions, and to isolate the variable that changed.

This is the essence of the scientific method applied to system administration: form a hypothesis based on observed differences, design an experiment that isolates the variable, and run it. The assistant does exactly that in this message, and the result is a clean, unambiguous success.

Conclusion

Message [msg 6383] is a masterclass in debugging by difference. Faced with a persistent GSP firmware initialization failure that survived SBR, the assistant recalled a previous success, identified the critical variable (nvidia module loading timing), designed a clean experiment, and executed it successfully. The message captures not just the solution but the reasoning process that produced it — the moment of "Wait — last session, the SBR DID work at one point" that every engineer recognizes as the turning point in a difficult debug session.

For anyone working with Blackwell GPUs, Linux PCI subsystem configuration, or IOMMU domain management, this message contains actionable knowledge: the GSP state survives SBR, and the correct recovery sequence requires letting nvidia autoload during PCI rescan rather than loading it manually afterward. But more broadly, it's a reminder that the most powerful debugging tool is not deep knowledge of the system — it's the ability to notice patterns, remember past outcomes, and systematically test hypotheses.