Re: [PATCH 1/7] iommupt: Remove the sanity check for pt_num_items_lg2() at the top level

[Mostafa Saleh <smostafa@google.com>]

On Mon, Jul 06, 2026 at 01:29:07PM -0300, Jason Gunthorpe wrote:
> This was ill conceived, the existing formats work OK because they
> happen to support pt_num_items_lg2() at the top level. However the
> documentation is clear that is not permitted because ARMv8 has
> concatenated top levels and we do not want to calculate an exact
> pt_num_items_lg2() for the top level special case.
> 
> The logic to compute the number of items of the top level is shown in
> pt_top_memsize_lg2() which is:
> 
> 	num_items_lg2 = common->max_vasz_lg2 - pt_table_item_lg2sz(&pts);
> 
> Which is pointless to try and sanity check.
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Reviewed-by: Mostafa Saleh <smostafa@google.com>

Thanks,
Mostafa

> ---
>  drivers/iommu/generic_pt/iommu_pt.h | 14 --------------
>  1 file changed, 14 deletions(-)
> 
> diff --git a/drivers/iommu/generic_pt/iommu_pt.h b/drivers/iommu/generic_pt/iommu_pt.h
> index c2752151c80af1..f1320c7e88dbbb 100644
> --- a/drivers/iommu/generic_pt/iommu_pt.h
> +++ b/drivers/iommu/generic_pt/iommu_pt.h
> @@ -1207,20 +1207,6 @@ static int pt_init_common(struct pt_common *common)
>  		     PT_FORCE_ENABLED_FEATURES))
>  		return -EOPNOTSUPP;
>  
> -	/*
> -	 * Check if the top level of the page table is too small to hold the
> -	 * specified maxvasz.
> -	 */
> -	if (!pt_feature(common, PT_FEAT_DYNAMIC_TOP) &&
> -	    top_range.top_level != PT_MAX_TOP_LEVEL) {
> -		struct pt_state pts = { .range = &top_range,
> -					.level = top_range.top_level };
> -
> -		if (common->max_vasz_lg2 >
> -		    pt_num_items_lg2(&pts) + pt_table_item_lg2sz(&pts))
> -			return -EOPNOTSUPP;
> -	}
> -
>  	if (common->max_oasz_lg2 == 0)
>  		common->max_oasz_lg2 = pt_max_oa_lg2(common);
>  	else
> -- 
> 2.43.0
>