Re: [PATCH] iommupt: Do not allow PTEs to be split when dirty logging

[Samiullah Khawaja <skhawaja@google.com>]

On Thu, Oct 15, 2026 at 02:20:10PM -0300, Jason Gunthorpe wrote:
>If a single PTE cannot be stored in the current bitmap that should be a
>failure and reported back to userspace. Allowing a PTE to be split creates
>a possibility that dirty memory will be reported as clean.
>
>The gather must also cover the entire PTE that is being cleaned, not just
>the part that fits within the bitmap.
>
>Fix both issues by computing the full IOVA range of every PTE and using
>that to update the bitmap and the gather. The bitmap code now rejects
>ranges that don't fit in it, and the gather always combined ranges.
>
>The selftest quietly relied on a bug where the CONT was split, that is why
>the half page size for the mock domain saw alternating dirties. Increase
>the dirty test page size to PAGE_SIZE so it still works as intended.
>
>Cc: stable@vger.kernel.org
>Fixes: 4a00f9434891 ("iommupt: Add read_and_clear_dirty op")
>Reported-by: Samarth Narang <samarth.colleges@gmail.com>
>Closes: https://lore.kernel.org/all/20261013165814.309255
>Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
>---
> drivers/iommu/generic_pt/iommu_pt.h     | 30 +++++++------------------
> tools/testing/selftests/iommu/iommufd.c | 10 ++++-----
> 2 files changed, 13 insertions(+), 27 deletions(-)
>
>This relies on other changes in the iommufd tree so I will take it
>

Reviewed-by: Samiullah Khawaja <skhawaja@google.com>