linux-kernel - Re: [PATCH for-next v3] RDMA/core: Avoid hmm_dma_map

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Message-ID: <aDQQyjJv9YKK_ZoV@infradead.org>
Date: Sun, 25 May 2025 23:57:14 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Leon Romanovsky <leon@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org, jgg@...pe.ca,
	zyjzyj2000@...il.com, Daisuke Matsuda <dskmtsd@...il.com>,
	hch@...radead.org
Subject: Re: [PATCH for-next v3] RDMA/core: Avoid hmm_dma_map_alloc() for
 virtual DMA devices

On Sun, May 25, 2025 at 03:51:08AM -0400, Leon Romanovsky wrote:
> 
> On Sat, 24 May 2025 14:43:28 +0000, Daisuke Matsuda wrote:
> > Drivers such as rxe, which use virtual DMA, must not call into the DMA
> > mapping core since they lack physical DMA capabilities. Otherwise, a NULL
> > pointer dereference is observed as shown below. This patch ensures the RDMA
> > core handles virtual and physical DMA paths appropriately.
> > 
> > This fixes the following kernel oops:
> > 
> > [...]
> 
> Applied, thanks!

So while this version look correct, the idea of open coding the
virtual device version of hmm_dma_map directly in the ODP code
is a nasty leaky abstraction.  Please pull it into a proper ib_dma_*
wrapper.