RE: [PATCH v5 07/15] iommupt: Add map_pages op

Tian, Kevin
2025-09-26T07:47:40Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Thursday, September 4, 2025 1:47 AM
>
> map is slightly complicated because it has to handle a number of special
> edge cases:
> - Overmapping a previously shared table with an OA - requries validating
> and freeing the possibly empty tables
> - Doing the above across an entire to-be-created contiguous entry
> - Installing a new shared table level concurrently with another thread
> - Expanding the table by adding more top levels

what is 'shared table'? Looks this term doesn't appear in previous patches.

also it's unclear to me why overmapping a previously shared table can
succeed while overmapping leaf entries cannot (w/ -EADDRINUSE)

> +
> + /* Calculate target page size and level for the leaves */
> + if (pt_has_system_page(common) && pgsize == PAGE_SIZE &&
> pgcount == 1) {
> + PT_WARN_ON(!(pgsize_bitmap & PAGE_SIZE));
> + if (log2_mod(iova | paddr, PAGE_SHIFT))
> + return -ENXIO;
> + map.leaf_pgsize_lg2 = PAGE_SHIFT;
> + map.leaf_level = 0;
> + single_page = true;
> + } else {
> + map.leaf_pgsize_lg2 = pt_compute_best_pgsize(
> + pgsize_bitmap, range.va, range.last_va, paddr);
> + if (!map.leaf_pgsize_lg2)
> + return -ENXIO;
> + map.leaf_level =
> + pt_pgsz_lg2_to_level(common, map.leaf_pgsize_lg2);

Existing driver checks alignment on pgsize, e.g. intel-iommu:

if (!IS_ALIGNED(iova | paddr, pgsize))
return -EINVAL;

But pt_compute_best_pgsize() doesn't use 'pgsize' and only have checks
on calculated pgsz_lg2:

pgsz_lg2 = log2_fls(pgsz_bitmap);
if (!pgsz_lg2)
return 0;

pgsz_lg2--;

PT_WARN_ON(log2_mod(va, pgsz_lg2) != 0);
PT_WARN_ON(oalog2_mod(oa, pgsz_lg2) != 0);

Looks not identical.

> +/**
> + * struct pt_iommu_flush_ops - HW IOTLB cache flushing operations
> + *
> + * The IOMMU driver should implement these using
> container_of(iommu_table) to
> + * get to it's iommu_domain dervied structure. All ops can be called in
> atomic
> + * contexts as they are buried under DMA API calls.

s/dervied/derived/