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

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Message-ID: <20250320053147.GB12560@lst.de>
Date: Thu, 20 Mar 2025 06:31:47 +0100
From: Christoph Hellwig <hch@....de>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc: Christoph Hellwig <hch@....de>, 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,
	Huan Yang <link@...o.com>
Subject: Re: [PATCH] mm/vmalloc: fix mischeck pfn valid in vmap_pfns

On Wed, Mar 19, 2025 at 05:09:06PM +0800, Gao Xiang wrote:
> The minimum map unit is page size instead of variable-size folio.
>
> For many cases, vmap (to combine many partial folios) is useful
> (instead of split all folios to order-0 folios in advance) but
> I agree page array may be inefficient.
>
> So I don't think another folio vmap() version is better overall
> anyway.

Then just reject the mappings for now.  vmap/vm_map_ram isn't really
intended for mapping totally arbitrary scattered memory anyway.
As mentioned before udmabuf also has a grave bug in the dma mapping
part, so just marking it broken would be another very sensible
option.