Re: [PATCH 3/5] x86/mm: Introduce and export interface arch_clean_nonsnoop_dma()

Jason Gunthorpe
2024-05-21T15:49:43Z

On Mon, May 20, 2024 at 07:07:10AM -0700, Christoph Hellwig wrote:
> On Tue, May 07, 2024 at 02:20:44PM +0800, Yan Zhao wrote:
> > Introduce and export interface arch_clean_nonsnoop_dma() to flush CPU
> > caches for memory involved in non-coherent DMAs (DMAs that lack CPU cache
> > snooping).
>
> Err, no. There should really be no exported cache manipulation macros,
> as drivers are almost guaranteed to get this wrong. I've added
> Russell to the Cc list who has been extremtly vocal about this at least
> for arm.

We could possibly move this under some IOMMU core API (ie flush and
map, unmap and flush), the iommu APIs are non-modular so this could
avoid the exported symbol.

Jason