[PATCH v4 0/5] iommu: Standardize ATS robustness and state tracking

[Pranjal Shrivastava <praan@google.com>]

The primary motivation for this series is an ATS state mismatch observed
under heavy load (via iova_stress). A failure in pci_enable_ats() leaves
IOMMU drivers like arm-smmu-v3 with inconsistent state leading to PCI core
warnings during device detach.

While David's recent work [1] addressed a discovery race for specific
quirked devices by moving them to the HEADER phase, gaps remained
regarding how Virtual Functions (VFs) inherit state from their Physical
Functions (PFs). Specifically, pci_ats_supported() did not account for
PF-level quirked status, and pci_prepare_ats() lacked STU validation for
VFs.

Based on discussion with Jason in v3 it was decided that IOMMU drivers 
should explicitly check pci_ats_supported before calling pci_prepare_ats
and the device probe should fail if pci_prepare_ats fails. Since these
early gates preclude software configuration errors, any remaining failure
during pci_enable_ats() is treated as a kernel bug & reported via WARN().

This series standardizes this pattern across ARM SMMUv3, Intel VT-d, &
AMD IOMMU drivers.

[1] https://lore.kernel.org/linux-pci/20260403222750.1215002-1-dmatlack@google.com/

[v4]
 - Standardized the pattern across Intel VT-d and AMD IOMMU drivers.
 - Replaced the SMMUv3 ats_prepared gate with a fatal probe-fail logic.
 - Utilized WARN() macros for runtime enablement failures in all drivers.
 - Collected R-b tags from Jason and Sami.

[v3] https://lore.kernel.org/all/20260519135323.1558777-1-praan@google.com/
[v2] https://lore.kernel.org/all/20260504163842.2692314-1-praan@google.com/

Pranjal Shrivastava (5):
  PCI/ATS: Ensure pci_ats_supported() is PF-aware for VFs
  PCI/ATS: Validate STU for VFs in pci_prepare_ats()
  iommu/arm-smmu-v3: Fix ATS state tracking
  iommu/vt-d: Fail probe on ATS configuration failure
  iommu/amd: Fail probe on ATS configuration failure

 drivers/iommu/amd/iommu.c                   | 27 ++++++++++++++++-----
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 21 +++++++++++++---
 drivers/iommu/intel/iommu.c                 | 15 +++++++++---
 drivers/pci/ats.c                           | 14 ++++++++---
 4 files changed, 61 insertions(+), 16 deletions(-)

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2.54.0.746.g67dd491aae-goog