[v4,0/5] iommu/arm-smmu, drm/msm: Fixes for stall-on-fault

Message

Connor Abbott March 4, 2025, 4:56 p.m. UTC

drm/msm uses the stall-on-fault model to record the GPU state on the
first GPU page fault to help debugging. On systems where the GPU is
paired with a MMU-500, there were two problems:

1. The MMU-500 doesn't de-assert its interrupt line until the fault is
   resumed, which led to a storm of interrupts until the fault handler
   was called. If we got unlucky and the fault handler was on the same
   CPU as the interrupt, there was a deadlock.
2. The GPU is capable of generating page faults much faster than we can
   resume them. GMU (GPU Management Unit) shares the same context bank
   as the GPU, so if there was a sudden spurt of page faults it would be
   effectively starved and would trigger a watchdog reset, made even
   worse because the GPU cannot be reset while there's a pending
   transaction leaving the GPU permanently wedged.

Patches 1-3 fixes the first problem and is independent of the rest of the
series. Patch 5 fixes the second problem and is dependent on patch 4, so
there will have to be some cross-tree coordination.

I've rebased this series on the latest linux-next to avoid rebase
troubles.

Signed-off-by: Connor Abbott <[e-mail]>
---
Changes in v4:
- Add patches 1-2, which fix reading registers in drm/msm when
  acknowledging the fault early. This was Robin's preferred solution
  compared to making drm/msm's fault handler tell arm-smmu to resume the
  fault.
- Link to v3: https://lore.kernel.org/r/[e-mail]

Changes in v3:
- Acknowledge the fault before resuming the transaction in patch 1.
- Add suggested extra context to commit messages.
- Link to v2: https://lore.kernel.org/r/[e-mail]

Changes in v2:
- Remove unnecessary _irqsave when locking in IRQ handler (Robin)
- Reuse existing spinlock for CFIE manipulation (Robin)
- Lock CFCFG manipulation against concurrent CFIE manipulation
- Don't use timer to re-enable stall-on-fault. (Rob)
- Use more descriptive name for the function that re-enables
  stall-on-fault if the cooldown period has ended. (Rob)
- Link to v1: https://lore.kernel.org/r/[e-mail]

---
Connor Abbott (5):
      iommu/arm-smmu: Save additional information on context fault
      iommu/arm-smmu-qcom: Don't read fault registers directly
      iommu/arm-smmu: Fix spurious interrupts with stall-on-fault
      iommu/arm-smmu-qcom: Make set_stall work when the device is on
      drm/msm: Temporarily disable stall-on-fault after a page fault

 drivers/gpu/drm/msm/adreno/a5xx_gpu.c            |  2 +
 drivers/gpu/drm/msm/adreno/a6xx_gpu.c            |  4 ++
 drivers/gpu/drm/msm/adreno/adreno_gpu.c          | 42 ++++++++++++-
 drivers/gpu/drm/msm/adreno/adreno_gpu.h          | 24 ++++++++
 drivers/gpu/drm/msm/msm_iommu.c                  |  9 +++
 drivers/gpu/drm/msm/msm_mmu.h                    |  1 +
 drivers/iommu/arm/arm-smmu/arm-smmu-qcom-debug.c |  4 +-
 drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c       | 64 ++++++++++++++-----
 drivers/iommu/arm/arm-smmu/arm-smmu.c            | 78 ++++++++++++++++++------
 drivers/iommu/arm/arm-smmu/arm-smmu.h            | 19 +++---
 10 files changed, 204 insertions(+), 43 deletions(-)
---
base-commit: 866e43b945bf98f8e807dfa45eca92f931f3a032
change-id: 20250117-msm-gpu-fault-fixes-next-96e3098023e1

Best regards,