[PATCH v7 07/15] iommupt: Add map_pages op

[Tian, Kevin]

> From: Jason Gunthorpe <jgg at nvidia.com>
> Sent: Friday, October 24, 2025 2:21 AM
> 
> map is slightly complicated because it has to handle a number of special
> edge cases:
>  - Overmapping a previously shared, but now empty, table level 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
> 
> Table expansion is a unique feature of AMDv1, this version is quite
> similar except we handle racing concurrent lockless map. The table top
> pointer and starting level are encoded in a single uintptr_t which ensures
> we can READ_ONCE() without tearing. Any op will do the READ_ONCE() and
> use
> that fixed point as its starting point. Concurrent expansion is handled
> with a table global spinlock.
> 
> When inserting a new table entry map checks that the entire portion of the
> table is empty. This includes freeing any empty lower tables that will be
> overwritten by an OA. A separate free list is used while checking and
> collecting all the empty lower tables so that writing the new entry is
> uninterrupted, either the new entry fully writes or nothing changes.
> 
> A special fast path for PAGE_SIZE is implemented that does a direct walk
> to the leaf level and installs a single entry. This gives ~15% improvement
> for iommu_map() when mapping lists of single pages.
> 
> This version sits under the iommu_domain_ops as map_pages() but does not
> require the external page size calculation. The implementation is actually
> map_range() and can do arbitrary ranges, internally handling all the
> validation and supporting any arrangment of page sizes. A future series
> can optimize iommu_map() to take advantage of this.
> 
> Tested-by: Alejandro Jimenez <alejandro.j.jimenez at oracle.com>
> Signed-off-by: Jason Gunthorpe <jgg at nvidia.com>

Reviewed-by: Kevin Tian <kevin.tian at intel.com>