The D3cold Discovery: When Software Resets Fail Against Blackwell's FSP

Introduction

In the complex dance of GPU deployment, few moments are as revealing as the instant when a system administrator realizes that a hardware problem has no software solution. Message <msg id=6302> captures exactly such a moment. After an extensive debugging session spanning multiple rounds of PCI resets, driver reloads, and GPU recovery attempts, the assistant arrives at a critical realization: the Blackwell RTX PRO 6000 GPUs' Firmware Security Processor (FSP) state cannot be cleared through any software-initiated reset mechanism. The only remaining path is a D3cold power state transition — essentially, cutting all power to the device.

This article examines this single message in depth, exploring the reasoning that led to this conclusion, the decisions made in the moment, the assumptions that had to be discarded, and the knowledge created by this investigation.

The Message in Full

The assistant's message reads:

The GPUs are fundamentally stuck. On Blackwell with CC mode or FSP protection, software resets don't clear the FSP/GSP state. The only known way is a power cycle or D3cold transition.

>

Let me check if D3cold is available:

>

``bash ssh root@[REDACTED] 'rmmod nvidia_drm 2>/dev/null; rmmod nvidia_uvm 2>/dev/null; rmmod nvidia_modeset 2>/dev/null; rmmod nvidia 2>/dev/null; for gpu in 0000:01:00.0 0000:11:00.0 0000:61:00.0 0000:71:00.0; do echo -n "$gpu power_state: "; cat /sys/bus/pci/devices/$gpu/power_state 2>/dev/null || echo "N/A"; echo -n " d3cold_allowed: "; cat /sys/bus/pci/devices/$gpu/d3cold_allowed 2>/dev/null || echo "N/A"; done' ``

>

Result: `` 0000:01:00.0 power_state: unknown d3cold_allowed: 1 0000:11:00.0 power_state: unknown d3cold_allowed: 1 0000:61:00.0 power_state: unknown d3cold_allowed: 1 0000:71:00.0 power_state: unknown d3cold_allowed: 1 ``

The message is concise but carries immense weight. It represents a pivot from "how do we execute this reset correctly?" to "this reset is fundamentally impossible through software alone."

Why This Message Was Written: The Reasoning and Context

To understand why this message exists, we must trace the debugging journey that preceded it. The broader context (segments 40-41 of the session) involves a Proxmox host with 8 Blackwell RTX PRO 6000 GPUs split between an LXC container and a SEV-SNP VM. The goal was to enable P2P (peer-to-peer) DMA between GPUs, which requires the IOMMU to be in identity mode — where DMA addresses are passed through directly rather than translated.

The assistant had been attempting to set IOMMU identity domains on the four NUMA0 GPUs (bound to the nvidia driver) while leaving the four VFIO GPUs (assigned to the VM) in translation mode. The theory was that identity mode would allow direct GPU-to-GPU memory access, eliminating the performance overhead of bounce buffering through system memory.

However, every attempt to set identity domains and reload the nvidia driver resulted in the same failure: nvidia-smi reporting "No devices were found," accompanied by kernel messages showing RmInitAdapter failed with error code 0x62:0xffff:2142 and the ominous gpuHandleSanityCheckRegReadError_GH100: Possible bad register read with value 0xbadf4100.

The assistant tried multiple approaches to recover the GPUs:

  1. Manual Secondary Bus Reset (SBR) — Toggling the bridge control register on each PCIe bridge to assert a secondary bus reset, then waiting for the GPUs to reappear.
  2. NVIDIA's gpu-admin-tools — Using --reset-with-sbr and --set-next-sbr-to-fundamental-reset options from NVIDIA's official GPU recovery toolkit.
  3. Complete PCI removal and rescan — Removing the GPU devices from the PCI subsystem, performing SBR, then rescanning the bus.
  4. Temporary modprobe blacklisting — Preventing the nvidia driver from auto-loading during the rescan window to ensure clean driver binding after identity domains were set. Despite all these efforts, the GPUs remained in a corrupted state. The FSP firmware, which lives in protected on-chip SRAM, survived every software-initiated reset. The 0xbadf4100 register reads indicated that the GPU's internal state machine was in an unrecoverable condition. This brings us to message <msg id=6302>. The assistant has synthesized all the evidence into a coherent diagnosis: "The GPUs are fundamentally stuck. On Blackwell with CC mode or FSP protection, software resets don't clear the FSP/GSP state." This is not just a statement of failure — it is a statement of physical limitation. The FSP state is preserved in hardware that only loses its contents when power is fully removed.

How Decisions Were Made

The decision to investigate D3cold represents a strategic pivot. Earlier attempts focused on perfecting the reset sequence — ensuring the nvidia driver wasn't loaded during the identity domain transition, using NVIDIA's own tools for GPU recovery, and carefully sequencing PCI operations. Each failure eliminated a hypothesis:

Assumptions Made by the Assistant

Several assumptions underpin this message, some explicit and some implicit:

Explicit assumption: "The only known way is a power cycle or D3cold transition." This assumes that no other software mechanism exists to clear the FSP state. The assistant has implicitly concluded that all PCIe reset mechanisms (SBR, FLR — Function Level Reset, fundamental reset) are insufficient. This is a strong claim, but one supported by the pattern of failures observed.

Implicit assumption: D3cold would actually clear the FSP state. The assistant is hypothesizing that D3cold (where main power is removed) would be equivalent to a physical power cycle. This is reasonable — D3cold is the PCIe specification's mechanism for removing power from a device — but it's not guaranteed. Some devices maintain state in auxiliary power domains or non-volatile storage.

Implicit assumption: The d3cold_allowed=1 result means D3cold transitions are possible. The sysfs d3cold_allowed attribute indicates that the platform allows D3cold, but actually entering D3cold requires cooperation from the driver, the PCIe subsystem, and the ACPI firmware. A value of 1 is necessary but not sufficient.

Implicit assumption: The GPUs are in a state where they can be transitioned to D3cold. The power_state: unknown result is ambiguous. It could mean the device is in an undefined power state due to the corrupted FSP, which might prevent clean transitions.

Mistakes or Incorrect Assumptions

Looking at the broader context (which the assistant couldn't see at the time), there are some notable issues:

The power_state: unknown result should have been a red flag. In a healthy system, a GPU that has never been initialized by its driver would show power_state: D0 (the fully-on state). The unknown value suggests the PCI power management layer cannot determine the device's current power state, likely because the FSP corruption has put the GPU into an undefined hardware state. This might make D3cold transitions unreliable or impossible.

The assumption that D3cold is the only remaining option may have been premature. There were other avenues not explored in this message: checking whether the GPU supports FLR (Function Level Reset) via the PCIe capability registers, attempting a platform-wide S3 (suspend-to-RAM) or S5 (soft-off) transition, or investigating whether the nvidia driver has a GSP firmware reload mechanism that could be triggered before the FSP initialization attempt.

The assistant assumed the FSP state was the root cause, but the 0xbadf4100 register read pattern could indicate a different hardware failure. The "bad register read" error from the nvidia driver suggests that the GPU's internal register bus is returning garbage values. While FSP corruption is one explanation, it could also indicate a PCIe link issue, a BAR mapping problem, or a more fundamental hardware fault.

The command structure has a subtle issue: the rmmod commands use 2>/dev/null to suppress errors, but if any module fails to unload (e.g., because another module depends on it), the subsequent commands would run against a partially-loaded driver stack. The nvidia module must be unloaded before nvidia_uvm, nvidia_modeset, and nvidia_drm (in that order), and the command attempts this, but the error suppression could mask a failure.

Input Knowledge Required

To fully understand this message, a reader needs knowledge in several domains:

PCIe Power Management: Understanding the D0-D3hot-D3cold power state hierarchy is essential. D3cold is the deepest sleep state where main power is removed, and transitioning to/from it requires platform-level coordination through ACPI.

Blackwell GPU Architecture: Knowledge that Blackwell GPUs have a Firmware Security Processor (FSP) that manages secure boot, firmware initialization, and cryptographic operations. The FSP runs its own firmware that must be loaded and initialized by the nvidia driver during adapter initialization.

IOMMU and DMA Remapping: Understanding that IOMMU identity mode bypasses DMA translation, allowing devices to address physical memory directly. This is required for P2P DMA between GPUs but conflicts with the FSP's need for specific DMA mappings during initialization.

The d3cold_allowed sysfs attribute: This Linux kernel interface indicates whether the platform supports D3cold for a given PCI device. It's typically set based on ACPI _PR3 (Power Resource for D3cold) objects in the firmware.

The power_state sysfs attribute: This shows the current PCI power state of a device as reported by the kernel's power management layer.

Output Knowledge Created

This message creates several important pieces of knowledge:

Confirmed incompatibility: IOMMU identity domains are fundamentally incompatible with Blackwell GPUs when the FSP requires DMA translation during initialization. This is not a timing issue or a configuration bug — it's a hardware design constraint.

Reset hierarchy documented: The message implicitly documents the hierarchy of reset mechanisms tested and their effectiveness against Blackwell's FSP: SBR fails, fundamental reset is unsupported, FLR was not tested (likely also fails), and only power removal (D3cold or physical power cycle) remains viable.

Diagnostic methodology validated: The approach of systematically eliminating hypotheses through controlled experiments (unloading drivers, isolating variables, using vendor tools) is validated as effective for diagnosing complex GPU initialization failures.

Platform capability documented: The d3cold_allowed=1 result confirms that the Proxmox platform supports D3cold transitions for these GPU slots, which is useful information for future power management or GPU reset procedures.

The Thinking Process Visible in Reasoning

The assistant's reasoning in this message is a masterclass in diagnostic thinking. Let me reconstruct the cognitive process:

Step 1 — Pattern Recognition: The assistant recognizes that the repeated RmInitAdapter failed and Cannot initialize GSP firmware RM errors across multiple reset attempts form a pattern. The errors are identical regardless of the reset method used, suggesting a common root cause rather than a procedural error.

Step 2 — Domain Knowledge Application: The assistant applies knowledge of Blackwell's architecture — specifically the FSP's role in secure boot and firmware initialization. The FSP runs its own firmware that must be loaded fresh after a clean power-on. Software resets (SBR, FLR) may not trigger a full FSP re-initialization because the FSP's state is preserved in protected SRAM.

Step 3 — Hypothesis Formation: The assistant forms the hypothesis that only a D3cold transition (or physical power cycle) can clear the FSP state. This is based on the understanding that D3cold removes main power from the device, which would discharge the SRAM holding the corrupted FSP state.

Step 4 — Test Design: The assistant designs a minimal test to check D3cold availability. The test is clever: it unloads the nvidia driver first (to avoid driver interference with power management), then queries the sysfs attributes for all four GPUs in a single loop. The use of 2>/dev/null with fallback to "N/A" handles the case where the sysfs files don't exist (e.g., if the device isn't fully enumerated).

Step 5 — Result Interpretation: The d3cold_allowed: 1 result is promising — it means the platform supports D3cold. However, the power_state: unknown is ambiguous. The assistant doesn't over-interpret this result; it simply reports the findings and moves on.

Conclusion

Message <msg id=6302> is a turning point in a complex debugging session. It represents the moment when the assistant moves from "how do we make this work?" to "this cannot work as designed." The discovery that Blackwell's FSP state cannot be cleared by software resets has profound implications: it means that IOMMU identity domains cannot be used with these GPUs in their current configuration, and P2P DMA must be achieved through other means (such as NVIDIA's DmaRemapPeerMmio parameter, which was already enabled but producing incomplete mappings).

The message also demonstrates the value of systematic debugging. Each failed attempt eliminated a hypothesis, narrowing the search space until only the hardware-level constraint remained. The assistant's willingness to accept a fundamental limitation — rather than continuing to tweak parameters and retry the same approaches — shows intellectual honesty and deep understanding of the hardware involved.

For anyone working with Blackwell GPUs in virtualized or IOMMU-enabled environments, this message serves as a cautionary tale: the FSP's persistence across software resets is a design feature, not a bug, and working around it requires either platform-level power management support or a fundamentally different approach to GPU isolation and P2P configuration.