Re: [PATCH v1 3/4] iommu: Avoid copying the user array twice in the full-array copy helper

[Baolu Lu]

On 6/4/26 05:26, Nicolin Chen wrote:
> iommu_copy_struct_from_full_user_array() copies a whole user array into a
> kernel buffer. In the common case, where user entry_len equals destination
> entry size, it takes a fast path and copies the whole array with a single
> copy_from_user().
>
> That fast path does not return, so it falls through into the item-by-item
> copy_struct_from_user() loop and copies every entry a second time. For an
> equal entry_len that loop is just a copy_from_user() of the same bytes, so
> the whole array is copied twice for no benefit.
>
> Return right after the bulk copy. The per-item loop then runs only on the
> slow path, where entry_len differs and each entry needs size adaption.
>
> Fixes: 4f2e59ccb698 ("iommu: Add iommu_copy_struct_from_full_user_array helper")
> Assisted-by:Claude:claude-opus-4-8
> Signed-off-by: Nicolin Chen<nicolinc@xxxxxxxxxx>
> ---
>   include/linux/iommu.h | 1 +
>   1 file changed, 1 insertion(+)

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>