This is an RFC to discuss the preservation of DMA allocations for
devices that are using direct allocation mode. Note preservation here
means preservation of physical memory only using KHO. IOVAs and IOMMU
mappings are out of scope.

The complexity and need of this was discussed in the thread mentioned
below. It was proposed to allow preservation of only a subset of
allocations with minimum support.

https://lore.kernel.org/all/aepfYzkI7NsVGCF0@google.com/
https://lore.kernel.org/all/aepRy7Gp7Ng85Zr7@willie-the-truck/

Note DMA allocation allows allocation from various allocators in various
configurations. This RFC supports preservation with,

- Direct Allocation Only.
- Pages allocated through alloc_page (Buddy allocator).
- No CMA support.
- No DMA allocators.

The changes are also pushed here:
https://github.com/samikhawaja/linux/tree/dma-alloc-preserve-direct

Looking forward to your feedback on this.

Thanks

Samiullah Khawaja (4):
  dma: Add DMA allocation preservation KHO ABI
  dma/pool: Add an API to check if DMA allocation is from pool
  dma-direct: Add API to preserve/restore allocations
  dma-mapping: Add API to preserve/restore DMA allocation

 include/linux/dma-direct.h        |  29 ++++++
 include/linux/dma-map-ops.h       |   1 +
 include/linux/dma-mapping.h       |  50 +++++++++
 include/linux/kho/abi/dma_alloc.h |  30 ++++++
 kernel/dma/Kconfig                |   3 +
 kernel/dma/direct.c               | 163 ++++++++++++++++++++++++++++++
 kernel/dma/mapping.c              |  52 ++++++++++
 kernel/dma/pool.c                 |  13 +++
 8 files changed, 341 insertions(+)
 create mode 100644 include/linux/kho/abi/dma_alloc.h


base-commit: 9974969c14031a097d6b45bcb7a06bb4aa525c40
prerequisite-patch-id: 41f13f37cb3b439f17dfa4e3f2d5c767aaef0346
-- 
2.54.0.545.g6539524ca2-goog

On Tue, May 05, 2026 at 12:23:16AM +0000, Samiullah Khawaja wrote:
>This is an RFC to discuss the preservation of DMA allocations for
>devices that are using direct allocation mode. Note preservation here
>means preservation of physical memory only using KHO. IOVAs and IOMMU
>mappings are out of scope.
>

Sorry, please ignore this separate cover letter email. It was sent by
mistake and has wrong prerequisite-patch-id.