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 and Baolu in v3/v5, it was decided that the
IOMMU drivers should explicitly check pci_ats_supported() before calling
pci_prepare_ats(). To enforce this, pci_prepare_ats() now noisily checks
for support via WARN_ON(). Furthermore, 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.

Following the discussion with the community, the driver-specific series
have been posted separately:

 - Intel IOMMU fixes reported by Sashiko [2]
 - Refactors for AMD IOMMU [3]

[1] https://lore.kernel.org/linux-pci/20260403222750.1215002-1-dmatlack@google.com/
[2] https://lore.kernel.org/all/20260531170254.60493-1-praan@google.com/
[3] https://lore.kernel.org/all/20260601134204.2150602-1-praan@google.com/

[v8]
 - Collected R-b tags from Kevin & Lu
 - Dropped the SMMU dev_iommu_priv_set(dev, NULL) patch.

[v7]
 - https://lore.kernel.org/all/20260601143644.2358771-1-praan@google.com/
 - Moved patch PCI/ATS: Mandate checking pci_ats_supported() before pci_prepare_ats()
    to the AMD series [3] to maintain bisectibility
 - Added a UAF fix for arm-smmu-v3 to set iommu->priv = NULL

[v6]
  - Reverted the decoupling of pci_ats_supported() from pci_prepare_ats().
  - Added a WARN_ON() to the internal support check in pci_prepare_ats().
  - Dropped the standalone Intel bugfixes (RB-tree and UAF) to be sent as a
   separate standalone series per maintainer request.
  - Kept the folded UAF fix in the AMD IOMMU patch to ensure the new error
   path is immediately safe.
  - Collected Reviewed-by tags from Lu Baolu for PCI core patches.

[v5]
  - https://lore.kernel.org/all/20260528202353.3422206-1-praan@google.com/
  - Decoupled pci_ats_supported() from pci_prepare_ats() in the PCI core.
  - Rebased SMMUv3 support on top of Nicolin Chen's "Always-On ATS" series.
  - Fixed pre-existing RB-tree corruption in VT-d probe (Baolu/Sashiko).
  - Addressed the pre-existing UAF in AMD IOMMU probe suggested by Sashiko.

[v4]
  - https://lore.kernel.org/all/20260525184347.4059549-1-praan@google.com/
  - 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.

Pranjal Shrivastava (4):
  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: Standardize ATS enablement failure reporting
  iommu/vt-d: Fail probe on ATS configuration failure

 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c |  7 ++++++-
 drivers/iommu/intel/iommu.c                 | 15 ++++++++++++---
 drivers/pci/ats.c                           | 13 ++++++++++---
 3 files changed, 28 insertions(+), 7 deletions(-)


base-commit: 542627e4a4aad76ccdf66436d7a8ea0d29069796
-- 
2.54.0.1032.g2f8565e1d1-goog