The Moment the GSP Died: Confronting Blackwell's Firmware Barrier

The Message

[assistant] nvidia-smi says no devices. The GSP issue again — vfio-pci corrupted the state. Let me check dmesg: [bash] ssh root@10.1.2.6 'dmesg | grep -E "NVRM.*(failed|error|Cannot|bad|WPR)" | tail -10' [ 2161.612703] NVRM: GPU0 kfspDumpDebugState_GB100: NV_PGSP_MAILBOX(1) = 0xbadf4100 [ 2161.612903] NVRM: GPU0 gpuHandleSanityCheckRegReadError_GH100: Possible bad register read: addr: 0x11080c, regvalue: 0xbadf4100, error code: Unknown SYS_PRI_ERROR_CODE [ 2161.613294] NVRM: GPU0 kfspDumpDebugState_GB100: NV_PGSP_MAILBOX(2) = 0xbadf4100 [ 2161.613491] NVRM: GPU0 gpuHandleSanityCheckRegReadError_GH100: Possible bad register read: addr: 0x110810, regvalue: 0xbadf4100, error code: Unknown SYS_PRI_ERROR_CODE

Context: The Quest for P2P DMA

To understand this message, one must first understand the long-running saga that preceded it. Across multiple segments spanning dozens of messages, the assistant had been pursuing a single, elusive goal: enabling GPU peer-to-peer (P2P) DMA on a system with 8 NVIDIA RTX PRO 6000 Blackwell GPUs, split between a host Linux machine (4 GPUs for inference) and a SEV-SNP confidential VM (4 GPUs). The complication was that the host required amd_iommu=on to support the SEV-SNP VM, and with IOMMU in full translation mode, GPU P2P DMA was blocked — the IOMMU would fault on peer accesses between GPUs.

The assistant had identified a promising solution: per-IOMMU-group identity domains. Linux kernel 6.14 supports switching individual IOMMU groups from the default DMA-FQ (translation) mode to identity (passthrough) mode via sysfs. By setting only the GPU groups to identity while leaving the VFIO groups in translation mode, P2P DMA could be restored without compromising the SEV-SNP VM's security. This approach had been tested at runtime in the previous session ([msg 6368]) and appeared to work — the kernel supported the switch, and the IOMMU groups could be toggled individually.

But there was a catch: the Blackwell GPUs have a Firmware Security Processor (FSP) — a dedicated management processor that runs firmware to handle GPU initialization, power management, and security functions. The nvidia driver establishes a session with the FSP during its initial probe. If the driver is unbound and rebound, the FSP retains locked state and refuses to reinitialize. This had been observed earlier when the assistant tried unbinding and rebinding GPUs at runtime — the FSP would enter a broken state, producing the telltale 0xbadf4100 mailbox errors.

The only viable path was to set identity domains at boot, before the nvidia driver first touched the GPUs. The assistant had prepared for this by creating a modprobe install hook that would switch the IOMMU groups to identity before the nvidia module loaded. The host was rebooted ([msg 6369]), and the assistant began verifying the result.

The Verification That Went Wrong

Message [msg 6376] shows the first verification attempt after the reboot. The assistant checked the IOMMU group types and found them correctly set to identity for all four NUMA0 GPU groups. The GPUs appeared to be bound to the nvidia driver. But then came the critical test: nvidia-smi returned "No devices were found."

This is the moment captured in message 6377. The assistant sees the empty nvidia-smi output and immediately recognizes the pattern: "The GSP issue again — vfio-pci corrupted the state." The dmesg output confirms the diagnosis with the familiar 0xbadf4100 error codes from the GSP (GPU System Processor, also referred to as FSP).

The sequence of events that led to this state is instructive. At boot, the modprobe hook correctly set the identity domains before the nvidia module loaded. The nvidia driver then probed the GPUs and established FSP sessions successfully — this much worked. But then the gpu-vfio-split.service ran. This service was designed to bind the NUMA1 GPUs (those destined for the SEV-SNP VM) to the vfio-pci driver by writing the GPU's PCI vendor and device ID (10de 2bb5) to vfio-pci's new_id attribute. The problem was that this new_id registration matched all GPUs with that PCI ID — including the four NUMA0 GPUs that should have remained on the nvidia driver. The vfio-pci driver, seeing a matching ID, claimed all eight GPUs, unbinding the NUMA0 GPUs from nvidia in the process.

When the assistant's identity script then ran (after vfio-split), it correctly unbounded the NUMA0 GPUs from vfio-pci and attempted to rebind them to nvidia. But the FSP had already been corrupted during the vfio-pci interlude. The nvidia driver could not re-establish its FSP session, leaving the GPUs in a state where they appeared in sysfs as bound to nvidia with identity domains, but were non-functional — nvidia-smi saw nothing.

The Thinking Process Revealed

This message is remarkable for what it reveals about the assistant's diagnostic process. The assistant does not merely report the failure; it immediately classifies it with a known pattern: "The GSP issue again." This tells us that the assistant has internalized a mental model of the Blackwell GPU architecture, where the GSP/FSP is a persistent stateful component that survives driver unbind/rebind cycles. The error codes 0xbadf4100 are not just random hex values — they are a signature the assistant has learned to recognize from previous encounters.

The assistant's reasoning chain is visible in the brevity and precision of the diagnosis. It knows that:

  1. nvidia-smi returning "No devices" while sysfs shows driver=nvidia means the GPU is registered with the PCI subsystem but the nvidia driver's initialization failed
  2. The specific dmesg errors (NV_PGSP_MAILBOX = 0xbadf4100, Possible bad register read) indicate GSP/FSP corruption
  3. The root cause is the vfio-pci interlude — the GPUs were briefly bound to vfio-pci, which does not manage the GPU firmware, leaving the FSP in an undefined state when nvidia tried to reclaim them The assistant also implicitly understands something deeper: the FSP corruption is not a transient software error. It persists across driver unbind/rebind cycles, across PCI remove/rescan operations, and even across Secondary Bus Reset (SBR). The only way to clear it is a full system power cycle — cutting power to the GPUs completely. This understanding drives the next phase of the investigation ([msg 6378]), where the assistant attempts increasingly aggressive hardware reset techniques: PCI remove, SBR, module blacklisting, and carefully sequenced driver loading.

Assumptions and Their Consequences

This message exposes several assumptions that, while reasonable, turned out to be incorrect.

Assumption 1: The boot-time identity domain approach would work. The assistant assumed that setting identity domains before the nvidia driver loaded would allow the driver to initialize the GPUs successfully with identity-mode IOMMU. This assumption was based on the idea that the nvidia driver's FSP initialization sequence is agnostic to the IOMMU translation mode. As later messages would reveal ([msg 6381] and the segment summary), this assumption was wrong — the Blackwell FSP boot sequence fails with error 0x177 when IOMMU is in identity mode, because the FSP requires specific DMA mappings set up by the kernel's DMA API, which only operates in translation mode.

Assumption 2: The service ordering could be fixed. The assistant assumed that the boot sequence could be restructured so that identity domains were set, then nvidia loaded, then vfio-split ran without disturbing the NUMA0 GPUs. The approach of having the identity script run after vfio-split to rebind the NUMA0 GPUs back to nvidia was based on the assumption that the FSP would survive the vfio-pci interlude. This turned out to be false — the FSP corruption from vfio-pci binding was irreversible without a full power cycle.

Assumption 3: SBR would reset the FSP. The assistant's next move ([msg 6378]) was to attempt PCI remove + Secondary Bus Reset + rescan, with the assumption that SBR would fully reset the GPU hardware, including the FSP. This was also incorrect — the Blackwell FSP survives SBR, FLR (Function-Level Reset), and CXL bus reset. It is designed to maintain state across all software-level resets for security reasons.

Input Knowledge Required

To fully grasp this message, the reader needs:

  1. Understanding of IOMMU and PCIe topology: The concept of IOMMU groups, DMA remapping, and how identity vs. translation modes affect DMA transactions. The system has 8 GPUs across two NUMA domains, each in its own IOMMU group.
  2. Blackwell GPU architecture: Knowledge that NVIDIA's Blackwell GPUs have a dedicated Firmware Security Processor (FSP) that handles initialization, power management, and security. The FSP runs its own firmware and maintains state independently of the GPU driver.
  3. The nvidia driver's GSP initialization sequence: The nvidia driver communicates with the GPU's GSP (GPU System Processor, a component of the FSP) during probe. If the GSP is in a bad state, the driver cannot complete initialization.
  4. vfio-pci driver behavior: Understanding that writing a PCI vendor/device ID to vfio-pci's new_id attribute causes vfio-pci to claim all devices matching that ID, not just specific ones. This is how the NUMA0 GPUs were accidentally grabbed.
  5. The 0xbadf4100 error signature: This specific mailbox error code is a known indicator of FSP corruption on Blackwell GPUs, encountered multiple times in previous sessions.
  6. The SEV-SNP constraint: The host requires amd_iommu=on for the confidential VM, which blocks GPU P2P DMA under default IOMMU configuration. This is the entire reason for the identity domain experiment.

Output Knowledge Created

This message produces several important pieces of knowledge:

  1. Confirmation that runtime driver rebinding corrupts Blackwell FSP: The pattern has now been observed multiple times — any unbind/rebind cycle (whether nvidia→vfio-pci→nvidia or nvidia→none→nvidia) leaves the FSP in a broken state.
  2. The boot-time approach is insufficient: Even with correct boot-time identity domain configuration, the service ordering problem (vfio-split grabbing all GPUs) defeated the approach. The fix requires either preventing vfio-split from touching NUMA0 GPUs or running the identity script before vfio-split with nvidia already loaded.
  3. A clear failure signature: The combination of nvidia-smi: No devices were found + sysfs showing driver=nvidia + dmesg showing 0xbadf4100 mailbox errors is a reliable diagnostic for FSP corruption.
  4. The need for a fundamentally different approach: This message marks the point where the assistant realizes that the current strategy is failing and begins exploring more aggressive hardware reset techniques (SBR, PCI remove/rescan). While these would also ultimately fail, the exploration generates valuable knowledge about the limits of software-level GPU reset.

The Broader Significance

Message 6377 is a turning point in the session. It represents the moment when a carefully planned approach — boot-time IOMMU identity domains — collides with the harsh reality of Blackwell GPU firmware behavior. The assistant had invested significant effort across multiple segments: identifying the IOMMU groups, creating the modprobe hook, setting up the service ordering, and rebooting the host. All of this was undone by a single service ordering issue: gpu-vfio-split.service claiming all GPUs via the new_id mechanism.

But the deeper significance is that even if the service ordering were fixed, the approach would still fail. As later messages would reveal, the Blackwell FSP simply cannot initialize under identity-mode IOMMU. The FSP's boot sequence requires DMA mappings that the kernel's DMA API provides only in translation mode. This is a fundamental hardware limitation, not a software configuration problem.

The message also showcases the assistant's diagnostic discipline. Faced with a failure, the assistant does not panic or guess. It checks the known error signature, confirms the pattern, and formulates a plan. The thinking is methodical: verify the symptom (nvidia-smi empty), check the known failure mode (dmesg GSP errors), identify the root cause (vfio-pci interlude), and plan the next steps (SBR-based reset). This pattern of systematic diagnosis is visible throughout the session and is particularly clear in this message.

For the reader, this message serves as a case study in the challenges of modern GPU system administration. The Blackwell GPU's FSP represents a new class of hardware complexity — a persistent, stateful management processor that cannot be reset through software means. This has profound implications for system administration workflows that involve driver rebinding, GPU hotplug, or PCIe resets. The traditional assumption that "unbind and rebind the driver" is a safe operation no longer holds for Blackwell GPUs. System administrators working with these GPUs must plan their boot-time driver binding strategy carefully, because any mistake that requires rebinding will necessitate a full power cycle to recover.