RE: [PATCH v6 4/5] iommu: Introduce pci_dev_reset_iommu_prepare/done()

Tian, Kevin
2025-11-21T07:59:15Z

> From: Nicolin Chen <nicolinc@nvidia.com>
> Sent: Wednesday, November 19, 2025 8:52 AM
>
> 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 r6.0, sec 10.3.1 IMPLEMENTATION NOTE recommends SW 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 all the attached RID/PASID
> domains
> group->blocking_domain so that the IOMMU hardware would fence any
> incoming
> ATS queries. And IOMMU drivers should also synchronously stop issuing new
> ATS invalidations and wait for all ATS invalidations to complete. This can
> avoid any ATS invaliation timeouts.
>
> However, if there is a domain attachment/replacement happening during an
> ongoing reset, ATS routines may be re-activated between the two function
> calls. So, introduce a new resetting_domain in the iommu_group structure
> to reject any concurrent attach_dev/set_dev_pasid call during a reset for
> a concern of compatibility failure. Since this changes the behavior of an
> attach operation, update the uAPI accordingly.
>
> Note that there are two corner cases:
> 1. Devices in the same iommu_group
> Since an attachment is always per iommu_group, this means that any
> sibling devices in the iommu_group cannot change domain, to prevent
> race conditions.
> 2. An SR-IOV PF that is being reset while its VF is not
> In such case, the VF itself is already broken. So, there is no point
> in preventing PF from going through the iommu reset.
>
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>