Re: [PATCH v7 04/22] dma: free atomic pool pages by physical address

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Jul 01, 2026 at 11:19:08AM +0530, Aneesh Kumar K.V (Arm) wrote:
> dma_direct_alloc_pages() may satisfy atomic allocations from the coherent
> atomic pools. The pool allocation is keyed by the virtual address stored in
> the gen_pool, but the pages API returns only the backing struct page.
> 
> On architectures with CONFIG_DMA_DIRECT_REMAP, atomic pool chunks are added
> to the gen_pool using their remapped virtual address.
> dma_direct_free_pages() reconstructs a linear-map address with
> page_address(page) and passes that to dma_free_from_pool(). That address
> does not match the gen_pool virtual range, so the pool lookup can fail and
> the code can fall through to freeing a pool-owned page through the normal
> page allocator path.
> 
> Add a page-based pool free helper that looks up the owning pool chunk by
> physical address, translates it back to the gen_pool virtual address, and
> frees that address to the pool. Use it from dma_direct_free_pages() while
> keeping the existing virtual-address helper for coherent allocation frees.
> 
> Tested-by: Michael Kelley <mhklinux@outlook.com>
> Tested-by: Mostafa Saleh <smostafa@google.com>
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
> ---
>  include/linux/dma-map-ops.h |  1 +
>  kernel/dma/direct.c         |  4 +--
>  kernel/dma/pool.c           | 54 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 57 insertions(+), 2 deletions(-)

This seems pretty suboptimal?

If !CONFIG_DMA_DIRECT_REMAP then page_to_virt() was used to compute
the genpool's addr so dma_free_from_pool_page() can use the same
logic, which is how things must be working at all today

The CONFIG_DMA_DIRECT_REMAP scenario does look broken, so I'm
surprised there isn't a Fixes line on this commit? I don't have an
opinion on the search, but since alloc_pages() is used there is 8
bytes in the struct page that could be used to store the remapped
vaddr to avoid the search if someday someone wants to improve
this. Maybe a small comment hinting that direction would be a nice
addition.

Jason