Re: [PATCH v9 0/4] iommu: Standardize ATS robustness and state tracking

[Pranjal Shrivastava <praan@google.com>]

On Mon, Jun 15, 2026 at 11:50:33PM +0000, Pranjal Shrivastava wrote:
> 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/
> 
> [v9]
>  - Collected R-b tags from Bjorn, Jason, Nicolin & Sami
>  - Folded in the dev_err into the WARN for arm-smmu-v3
> 

[...]

> 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 |  9 +++++++--
>  drivers/iommu/intel/iommu.c                 | 15 ++++++++++++---
>  drivers/pci/ats.c                           | 13 ++++++++++---
>  3 files changed, 29 insertions(+), 8 deletions(-)
> 
> 
> base-commit: 6666bde33b83cb4fc9b1f7ba6a3471479f76ce72

Hi Joerg / Will, 

Gentle ping on this, please LMK if anything else needs to be done for
this seris?

Thanks,
Praan