Re: [PATCH] dma-mapping: remove bogus test for pfn_valid from dma_map_resource

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, May 08, 2026 at 06:01:01PM +0800, Jianpeng Chang wrote:
> > As I said last time, I think pfn_valid() && !PageReserved(pfn_to_page())
> > would be enough for what we want here, although now it's strictly under
> > CONFIG_DMA_API_DEBUG, perhaps the overhead of memblock_is_map_memory()
> > might be less of an issue. Either way though, now that it's all
> > channelled through the single dma_map_phys() path, it would probably
> > make sense to consolidate any MMIO sanity-checking into
> > dma_debug_map_phys() anyway :/

> Thanks for the suggestion. Move the check into debug_dma_map_phys() is
> indeed better, and I will replace pfn_valid() with pfn_valid() &&
> !PageReserved() as you suggested.

I'm not sure that is right. IIRC pfn_valid() is true for ZONE_DEVICE
P2P pages that are used with map_phys but never with map_resource.

PageReserved isn't enough to fix it.

Jason