[PATCH v3 0/5] Disable ATS via iommu during PCI resets

Nicolin Chen
2025-08-11T23:00:26Z

Hi all,

PCIe permits a device to ignore ATS invalidation TLPs, while processing a
reset. This creates a problem visible to the OS where an ATS invalidation
command will time out: e.g. an SVA domain will have no coordination with a
reset event and can racily issue ATS invalidations to a resetting device.

The OS should do something to mitigate this as we do not want production
systems to be reporting critical ATS failures, especially in a hypervisor
environment. Broadly, OS could arrange to ignore the timeouts, block page
table mutations to prevent invalidations, or disable and block ATS.

The PCIe spec in sec 10.3.1 IMPLEMENTATION NOTE recommends to disable and
block ATS before initiating a Function Level Reset. It also mentions that
other reset methods could have the same vulnerability as well.

Provide a callback from the PCI subsystem that will enclose the reset and
have the iommu core temporarily change domains to group->blocking_domain,
so IOMMU drivers would fence any incoming ATS queries, synchronously stop
issuing new ATS invalidations, and wait for existing ATS invalidations to
complete. Doing this can avoid any ATS invaliation timeouts.

When a device is resetting, any new domain attachment should be deferred,
until the reset is finished, to prevent ATS activity from being activated
between the two callback functions. Introduce a new pending_reset flag to
allow iommu core to cache the target domains in the SW level but bypass
the driver-level attachment. Later, iommu_dev_reset_done() will re-attach
these soft-attached domains via __iommu_attach_device/set_group_pasid().

Finally, apply these iommu_dev_reset_prepare/done() functions in the PCI
reset functions.

This is on Github:
https://github.com/nicolinc/iommufd/commits/iommu_dev_reset-v3

Changelog
v3
* Add Reviewed-by from Jason
* [iommu] Add a fast return in iommu_deferred_attach()
* [iommu] Update kdocs, inline comments, and commit logs
* [iommu] Use group->blocking_domain v.s. ops->blocked_domain
* [iommu] Drop require_direct, iommu_group_get(), and xa_lock()
* [iommu] Set the pending_reset flag after RID/PASID domain setups
* [iommu] Do not bypass PASID domains when RID domain is already the
blocking_domain
* [iommu] Add iommu_get_domain_for_dev_locked to correctly return the
blocking_domain
v2
https://lore.kernel.org/all/cover.1751096303.git.nicolinc@nvidia.com/
* [iommu] Update kdocs, inline comments, and commit logs
* [iommu] Replace long-holding group->mutex with a pending_reset flag
* [pci] Abort reset routines if iommu_dev_reset_prepare() fails
* [pci] Apply the same vulnerability fix to other reset functions
v1
https://lore.kernel.org/all/cover.1749494161.git.nicolinc@nvidia.com/

Thanks
Nicolin

Nicolin Chen (5):
iommu: Lock group->mutex in iommu_deferred_attach
iommu: Pass in gdev to __iommu_device_set_domain
iommu: Add iommu_get_domain_for_dev_locked() helper
iommu: Introduce iommu_dev_reset_prepare() and iommu_dev_reset_done()
pci: Suspend iommu function prior to resetting a device

include/linux/iommu.h | 13 ++
.../arm/arm-smmu-v3/arm-smmu-v3-iommufd.c | 2 +-
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 9 +-
drivers/iommu/arm/arm-smmu/qcom_iommu.c | 2 +-
drivers/iommu/dma-iommu.c | 2 +-
drivers/iommu/fsl_pamu_domain.c | 2 +-
drivers/iommu/iommu.c | 205 +++++++++++++++++-
drivers/iommu/ipmmu-vmsa.c | 2 +-
drivers/iommu/msm_iommu.c | 2 +-
drivers/iommu/mtk_iommu.c | 2 +-
drivers/iommu/omap-iommu.c | 2 +-
drivers/iommu/tegra-smmu.c | 2 +-
drivers/pci/pci-acpi.c | 17 +-
drivers/pci/pci.c | 68 +++++-
drivers/pci/quirks.c | 23 +-
15 files changed, 323 insertions(+), 30 deletions(-)

--
2.43.0