Re: [PATCH] iommu: Ensure .iotlb_sync is called correctly

Jon Hunter
2026-04-08T17:29:12Z

On 08/04/2026 15:40, Robin Murphy wrote:
> Many drivers have no reason to use the iotlb_gather mechanism, but do
> still depend on .iotlb_sync being called to properly complete an unmap.
> Since the core code is now relying on the gather to detect when there
> is legitimately something to sync, it should also take care of encoding
> a successful unmap when the driver does not touch the gather itself.
>
> 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
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> drivers/iommu/iommu.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 50718ab810a4..ee83850c7060 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2717,6 +2717,12 @@ static size_t __iommu_unmap(struct iommu_domain *domain,
>
> pr_debug("unmapped: iova 0x%lx size 0x%zx\n",
> iova, unmapped_page);
> + /*
> + * If the driver itself isn't using the gather, make sure
> + * it looks non-empty so iotlb_sync will still be called.
> + */
> + if (iotlb_gather->start >= iotlb_gather->end)
> + iommu_iotlb_gather_add_range(iotlb_gather, iova, size);
>
> iova += unmapped_page;
> unmapped += unmapped_page;

Tested-by: Jon Hunter <jonathanh@nvidia.com>

Thanks!
Jon

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