linux-kernel - Re: [PATCH] mm/vmalloc: fix mischeck pfn valid in vmap

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Message-ID: <Z-DKKQcc0dSdSrw8@casper.infradead.org>
Date: Mon, 24 Mar 2025 02:57:45 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Christoph Hellwig <hch@....de>
Cc: Huan Yang <link@...o.com>, akpm@...ux-foundation.org,
	bingbu.cao@...ux.intel.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, lorenzo.stoakes@...cle.com,
	opensource.kernel@...o.com, rppt@...nel.org, ryan.roberts@....com,
	urezki@...il.com, ziy@...dia.com, vivek.kasireddy@...el.com,
	"Vishal Moola (Oracle)" <vishal.moola@...il.com>
Subject: Re: [PATCH] mm/vmalloc: fix mischeck pfn valid in vmap_pfns

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@gmail.com/
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.