Re: [PATCH] mm/vmalloc: fix mischeck pfn valid in vmap_pfns

[Matthew Wilcox]

On Tue, Mar 18, 2025 at 09:33:30AM +0100, Christoph Hellwig wrote:
> On Tue, Mar 18, 2025 at 04:20:17PM +0800, Huan Yang wrote:
> > This prevents us from properly invoking vmap, which is why we have turned to using vmap_pfn instead.
> >
> > Even if a folio-based vmap is implemented, it still cannot handle mapping multiple folio ranges of physical
> >
> > memory to vmalloc regions. A range of folio is important, it maybe an offset in memfd, no need entire folio.
> >
> > So, I still consider vmap_pfn to be the optimal solution for this specific scenario. :)
> 
> No, vmap_pfn is entirely for memory not backed by pages or folios,
> i.e. PCIe BARs and similar memory.  This must not be mixed with proper
> folio backed memory.
> 
> So you'll need a vmap for folios to support this use case.

https://lore.kernel.org/linux-mm/20250131001806.92349-1-vishal.moola@xxxxxxxxx/
seems like a good match for "we need to vmap a range from a file".

Vishal has some updates since this version, and I'm sure he can send
them out after LSFMM.