[PATCH stable 6.12 0/2] iommu/vt-d+dma: fix stale DMA PTE WARN on IOVA reuse (regression v6.12.75)

[avinash pal]

Two-patch series addressing the stale-DMA-PTE WARN_ON regression that
hits kernels 6.12.75 and 6.12.76 when Intel IOMMU is enabled.

  Bugzilla : https://bugzilla.kernel.org/show_bug.cgi?id=221389
  Unaffected: v6.12.74   (confirmed: Giovanni Pancotti, 2026-04-22)
  Affected  : v6.12.76   (WARN on ATA/SCSI DMA workloads)
  Workaround: intel_iommu=off

Root cause
==========
The lazy-flush path in __iommu_dma_unmap_sg() releases an IOVA back to
the allocator via free_iova_fast() before iommu_iotlb_sync() drains the
hardware TLB.  A concurrent map() on the same domain receives the same
IOVA and hits a live PTE in __domain_mapping():

  CPU 0 (unmap, lazy path)        CPU 1 (concurrent map)
  ──────────────────────────      ───────────────────────────────
  iommu_unmap(iova)
  free_iova_fast(iova)  ← live
                                  alloc_iova_fast() → same iova
                                  __domain_mapping()
                                    dma_pte_present() == true
                                    WARN_ON_ONCE()          ← hit

Patches
=======
1/2  iommu/vt-d: fail map loudly on stale DMA PTE
     - Replaces bare WARN(1,...) with pr_err_ratelimited + WARN_ON_ONCE
     - Prints vPFN + old PTE value for debugging
     - Returns -EEXIST; no silent double-map

2/2  iommu/dma: sync IOTLB before releasing IOVA on sg unmap
     - Adds iommu_iotlb_sync() before free_iova_fast() on lazy path
     - Closes the race window; strict-mode path already does this

ACTION NEEDED by reviewer: run
  git log v6.12.74..v6.12.76 -- drivers/iommu/dma-iommu.c
to identify the offending commit for the Fixes: tag in patch 2/2.

avinash pal (2):
  iommu/vt-d: fail map loudly on stale DMA PTE
  iommu/dma: sync IOTLB before releasing IOVA on sg unmap

 drivers/iommu/dma-iommu.c   |  9 +++++++
 drivers/iommu/intel/iommu.c | 50 ++++++++++++++++++++++++++++---------
 2 files changed, 47 insertions(+), 12 deletions(-)


base-commit: 444b39ef6108313e8452010b22aaba588e8fb92b
-- 
2.53.0