Re: [PATCH v6 08/39] mm: add mmap action for discontiguous kernel page mapping

On 10/13/26 17:04, Lorenzo Stoakes (ARM) wrote:

The existing kernel page mapping mmap actions allow for partial and full
mapping of an array of struct page pointers.

However some drivers require the mapping of discontiguous ranges. Permit
this by providing discontig_kernel_page_ops which allows a driver to
specify how the operation should begin and how batches of pages should be
retrieved.

It uses the minimum exposed interface to do so, providing address, page
offset and both vm_private_data state and a local private state object.

ops->init can establish state for the operation, and ops->get outputs the
pages to map and their count. Should an error arise the core unmaps the
VMA, invoking vm_ops->close, which is therefore where any state established
by ops->init is released.

Also update the compatibility layer to do this too via
compat_mmap_action_abort().

Batches may not exceed the VMA, but may map less than its full range in
case the driver wishes to allow the user to map an area larger than the
available data.

To use it, users invoke mmap_action_map_discontig_kernel_pages() with
initial local private state and a set of operations.

Users can then use one of the provided helper functions to perform an
action:

* discontig_kernel_map_abort() - Abort and leave the mapping as it has
  been accumulated so far.
* discontig_kernel_map_page() - Map a single page, or a compound page given
  its head page, as 1..N contiguous pages.
* discontig_kernel_map_pages() - Map a struct page ** array of a specified
  count, mapping only those pages which fit in the VMA.

The userland VMA tests are updated accordingly.

Acked-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
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[...]

... indentation ;)

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David