Re: [PATCH v4] PCI: Ensure ATS disabled via quirk before notifying IOMMU drivers

On 8/18/26 04:28, David Matlack wrote:
> Ensure that PCI devices always have ATS disable via quirk before IOMMU
> drivers are notified about the device. Fix this by converting the
> existing quirks from final to header fixups and changing the quirk logic
> to set a new no_ats bit in struct pci_dev that prevents pci_dev.ats_cap
> from ever getting set.
> 
> Use header fixups instead of early fixups since not enough of struct
> pci_dev is set up in during early fixups: quirk_amd_harvest_no_ats()
> needs subsystem_device and subsystem_vendor to be set.
> 
> This change ensures that pci_ats_supported() always takes quirks into
> account during iommu_ops.probe_device(), when IOMMU drivers are notified
> about devices, and that pci_ats_supported() returns the same value when
> the device is released in iommu_ops.release_device().
> 
> The Intel IOMMU driver uses pci_ats_supported() in probe/release to
> determine whether to add/remove a device from a tracking rbtree. This
> strict reliance on pci_ats_supported() remaining constant between probe
> and release was introduced by commit 89436f4f5412 ("iommu/vt-d: Fix
> WARN_ON in iommu probe path"). Because FINAL quirks evaluate too late
> (in pci_bus_add_device()), pci_ats_supported() evaluated to true during
> IOMMU probe but false during release. This mismatch bypassed the rbtree
> removal upon device release, leading to a later use-after-free.
> 
> Note that this fix only matters for PCI devices created after IOMMU bus
> notifiers are set up (e.g. hot-plugged devices and VFs).
> 
> Fixes: a18615b1cfc0 ("PCI: Disable ATS for specific Intel IPU E2000 devices")
> Fixes: 9b44b0b09dec ("PCI: Mark AMD Stoney GPU ATS as broken")
> Fixes: 3f1271b54edc ("PCI: Mark all AMD Navi10 and Navi14 GPU ATS as broken")
> Closes:https://lore.kernel.org/linux-iommu/[email protected]/
> Reviewed-by: Pranjal Shrivastava<[email protected]>
> Tested-by: Pranjal Shrivastava<[email protected]>
> Signed-off-by: David Matlack<[email protected]>
> ---
> v4:
>   - Rebase onto tip of Linus' tree
>   - Add Pranjal's Reviewed-by and Tested-by tags
> 
> v3:https://lore.kernel.org/linux-pci/20260403222750.1215002-1- 
> [email protected]/
> v2:https://lore.kernel.org/linux-pci/20260327211649.3816010-1- 
> [email protected]/
> v1:https://lore.kernel.org/linux-pci/20260223184017.688212-1- 
> [email protected]/
> 
> Cc: Raghavendra Rao Ananta<[email protected]>
> Cc: David Woodhouse<[email protected]>
> Cc: Lu Baolu<[email protected]>
> Cc: Andy Shevchenko<[email protected]>
> 
>   drivers/pci/ats.c    |  2 +-
>   drivers/pci/quirks.c | 50 ++++++++++++++++++++++----------------------
>   include/linux/pci.h  |  1 +
>   3 files changed, 27 insertions(+), 26 deletions(-)

Reviewed-by: Lu Baolu <[email protected]>