Re: [PATCH rc 5/5] iommupt: Fix the end_index calculation in __map_range_leaf()

[Pranjal Shrivastava <praan@google.com>]

On Tue, May 12, 2026 at 01:46:17PM -0300, Jason Gunthorpe wrote:
> Sashiko noticed a mismatch of units in this math: num_leaves is
> actually the number of leaf *entries* (so a 16-item contiguous leaf
> is one num_leaves), while index is in items. The mismatch in maths
> causes __map_range_leaf() to exit early instead of efficiently
> filling a larger range of contiguous PTEs.
> 
> The early exit is caught by the functions above and then
> __map_range_leaf() is re-invoked, so there is no functional issue.
> 
> Correct the misuse of units by adjusting num_leaves with the leaf
> size and avoid the performance cost of looping externally.
> 
> There are also some mismatched types for num_leaves; simplify
> things to remove the duplicated calculations.
> 
> Fixes: d6c65b0fd621 ("iommupt: Avoid rewalking during map")
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

This is an important catch! It means that today, we were redundantly
re-walking the upper page table levels.

Reviewd-by: Pranjal Shrivastava <praan@google.com>

Thanks!