Re: [PATCH v1 2/2] iommu/arm-smmu-v3: Recover ATC invalidate timeouts

[Samiullah Khawaja]

On Fri, Mar 06, 2026 at 09:00:06AM -0400, Jason Gunthorpe wrote:
> On Fri, Mar 06, 2026 at 11:22:52AM +0800, Baolu Lu wrote:
> > I believe this issue is not unique to the arm-smmu-v3 driver. Device ATC
> > invalidation timeout is a generic challenge across all IOMMU
> > architectures that support PCI ATS. Would it be feasible to implement a
> > common 'fencing and recovery' mechanism in the IOMMU core so that all
> > IOMMU drivers could benefit?
>
> I think yes, for parts, but the driver itself has to do something deep
> inside it's invalidation to allow the flush to complete without
> exposing the system to memory corruption - meaning it has to block
> translated requests before completing the flush

Yes and currently the underlying drivers have software timeouts
(AMD=100millisecond, arm-smmu-v3=1second) defined which could timeout
before the actual ATC invalidation timeout occurs. Do you think maybe
the timeout needs to be propagated to the caller (flush callback) so the
memory/IOVA is not allocated to something else? Or blocking translated
requests for such devices should be enough?
> I don't see how that can be made too generalized since we are running
> this flush stuff in irq and reclaim contexts, it has to be very small
> and targtted without memory allocation or sleeping locks.

> Jason