linux-kernel - Re: [PATCH v5 0/4] UIO_MEM_DMA

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Message-ID: <ZcE8JC0o9swkNzmr@rhel-developer-toolbox-latest>
Date: Mon, 5 Feb 2024 11:51:00 -0800
From: Chris Leech <cleech@...hat.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nilesh Javali <njavali@...vell.com>, Christoph Hellwig <hch@....de>,
	John Meneghini <jmeneghi@...hat.com>, Lee Duncan <lduncan@...e.com>,
	Mike Christie <michael.christie@...cle.com>,
	Hannes Reinecke <hare@...nel.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	GR-QLogic-Storage-Upstream@...vell.com
Subject: Re: [PATCH v5 0/4] UIO_MEM_DMA_COHERENT for cnic/bnx2/bnx2x

On Mon, Feb 05, 2024 at 05:57:58PM +0100, Alexander Lobakin wrote:
> From: Chris Leech <cleech@...hat.com>
> Date: Thu,  1 Feb 2024 15:33:56 -0800
> 
> > During bnx2i iSCSI testing we ran into page refcounting issues in the
> > uio mmaps exported from cnic to the iscsiuio process, and bisected back
> > to the removal of the __GFP_COMP flag from dma_alloc_coherent calls.
> 
> IIRC Jakub mentioned some time ago that he doesn't want to see
> third-party userspace <-> kernel space communication in the networking
> drivers, to me this looks exactly like that :z

This isn't something anyone likes, but it's an interface that's been in
the kernel and in use since 2009.  I'm trying to see if it can be fixed
"enough" to keep existing users functioning.  If not, maybe the cnic
interface and the stacking protocol drivers (bnx2i/bnx2fc) should be
marked as broken.

- Chris