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

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Message-ID: <20250526090722.GY7435@unreal>
Date: Mon, 26 May 2025 12:07:22 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Christoph Hellwig <hch@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org, jgg@...pe.ca,
	zyjzyj2000@...il.com, Daisuke Matsuda <dskmtsd@...il.com>
Subject: Re: [PATCH for-next v3] RDMA/core: Avoid hmm_dma_map_alloc() for
 virtual DMA devices

On Sun, May 25, 2025 at 11:57:14PM -0700, Christoph Hellwig wrote:
> 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.

I did it on purpose as these ib_dma_* are used by all IB users (core, drivers
and ULPs) and at this point I don't want them to use any of that specific API.

Thanks