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

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Apr 23, 2026 at 03:39:02PM +0530, avinash pal wrote:
> 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
> 
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>