Re: [PATCH v2] iommu: Always fill in gather when unmapping

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Apr 02, 2026 at 11:25:16AM -0300, Jason Gunthorpe wrote:
> The fixed commit assumed that the gather would always be populated if an
> iotlb_sync was required.
> 
> arm-smmu-v3, amd, VT-d, riscv, s390, and mtk all use information from the
> gather during their iotlb_sync() and this approach works for them.
> 
> However, arm-smmu, qcom_iommu, ipmmu-vmsa, sun50i, sprd, virtio, and
> apple-dart all ignore the gather during their iotlb_sync(). They mostly
> issue a full flush.
> 
> Unfortunately the latter set of drivers often don't bother to add anything
> to the gather since they don't intend on using it. Since the core code now
> blocks gathers that were never filled, this caused those drivers to stop
> getting their iotlb_sync() calls and breaks them.
> 
> Since it is impossible to tell the difference between gathers that are
> empty because there is nothing to do and gathers that are empty because
> they are not used, fill in the gathers for the missing cases.
> 
> mtk uses io-pgtable-arm-v7s but added the range to the gather in the unmap
> callback. Move this into the io-pgtable-arm-v7s unmap itself. That will
> fix all the armv7 using drivers (arm-smmu, qcom_iommu, ipmmu-vmsa).
> 
> io-pgtable-arm needs to accommodate drivers like arm-smmu that don't want
> to use the gather by just adding a simple range, and drivers like SMMUv3
> that need to use gather->pgsize and also have a disjoint check. Move
> SMMUv3 to a new tlb_add_range() op which replaces calling
> iommu_iotlb_gather_add_page() in a loop with a single call to update the
> gather with the range and required pgsize.
> 
> iommu_iotlb_gather_add_page() is repurposed since nothing but SMMUv3 uses it
> now that amd, VT-d and riscv are using iommupt.
> 
> Add a trivial gather population to io-pgtable-dart.
> 
> Add trivial populations to sprd, sun50i and virtio-iommu in their unmap
> functions.
> 
> Fixes: 90c5def10bea ("iommu: Do not call drivers for empty gathers")
> Reported-by: Jon Hunter <jonathanh@nvidia.com>
> Closes: https://lore.kernel.org/r/8800a38b-8515-4bbe-af15-0dae81274bf7@nvidia.com
> Tested-by: Jon Hunter <jonathanh@nvidia.com>
> Acked-by: Pranjal Shrivastava <praan@google.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 11 ++++++-----
>  drivers/iommu/io-pgtable-arm-v7s.c          |  4 ++++
>  drivers/iommu/io-pgtable-arm.c              | 19 ++++++++++++++++---
>  drivers/iommu/io-pgtable-dart.c             |  3 +++
>  drivers/iommu/mtk_iommu.c                   |  1 -
>  drivers/iommu/sprd-iommu.c                  |  1 +
>  drivers/iommu/sun50i-iommu.c                |  1 +
>  drivers/iommu/virtio-iommu.c                |  2 ++
>  include/linux/io-pgtable.h                  |  3 +++
>  include/linux/iommu.h                       | 19 ++++++++++---------
>  10 files changed, 46 insertions(+), 18 deletions(-)
> 

<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>