Re: [PATCH rc 3/5] iommu: Handle unmap error when iommu_debug is enabled

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, May 13, 2026 at 03:13:41PM +0000, Mostafa Saleh wrote:
> On Tue, May 12, 2026 at 01:46:15PM -0300, Jason Gunthorpe wrote:
> > Sashiko noticed a latent bug where the map error flow called iommu_unmap()
> > which calls iommu_debug_unmap_begin()/iommu_debug_unmap_end() however
> > since this is an error path the map flow never actually established the
> > original iommu_debug_map() it will malfunction.
> > 
> > Lift the unmap error handling into iommu_map_nosync() and reorder it so
> > the trace_map()/iommu_debug_map() records the partial mapping and then
> > immediately unmaps it. This avoid creating the unbalanced tracking and
> > provides saner tracing instead of a unmap unmatched to any map.
> 
> There is usually littel coverage in such paths, I have been thinking
> of creating some test-suites on the IOMMU and io-pgtable/SMMUv3 level
> to cover some of the failure cases and some of the tricky page table
> operations, the problem is that there are many things to cover (starting
> from the crashes/logical issues till TLB invalidation correctness of
> some operations).

I think the existing kunit for iommupt would have caught this if it is run
with the debug option. I didn't test the io-pgtable stuff but I'm
working on removing more of that..

Jason