netdev - Re: [PATCH 3/3] cnic,bnx2,bnx2x: use UIO_MEM_DMA

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Date: Mon, 2 Oct 2023 10:46:05 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Jerry Snitselaar <jsnitsel@...hat.com>
Cc: Christoph Hellwig <hch@....de>, Hannes Reinecke <hare@...e.de>,
	Chris Leech <cleech@...hat.com>, Rasesh Mody <rmody@...vell.com>,
	Ariel Elior <aelior@...vell.com>,
	Sudarsana Kalluru <skalluru@...vell.com>,
	Manish Chopra <manishc@...vell.com>,
	Nilesh Javali <njavali@...vell.com>,
	Manish Rangankar <mrangankar@...vell.com>,
	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
Subject: Re: [PATCH 3/3] cnic,bnx2,bnx2x: use UIO_MEM_DMA_COHERENT

On Mon, Oct 02, 2023 at 12:50:21AM -0700, Jerry Snitselaar wrote:
> On Mon, Oct 02, 2023 at 08:04:24AM +0200, Christoph Hellwig wrote:
> > On Sun, Oct 01, 2023 at 07:22:36AM -0700, Jerry Snitselaar wrote:
> > > Changes last year to the dma-mapping api to no longer allow __GFP_COMP,
> > > in particular these two (from the e529d3507a93 dma-mapping pull for
> > > 6.2):
> > 
> > That's complete BS.  The driver was broken since day 1 and always
> > ignored the DMA API requirement to never try to grab the page from the
> > dma coherent allocation because you generally speaking can't.  It just
> > happened to accidentally work the trivial dma coherent allocator that
> > is used on x86.
> > 
> 
> re-sending since gmail decided to not send plain text:
> 
> Yes, I agree that it has been broken and misusing the API. Greg's
> question was what changed though, and it was the clean up of
> __GFP_COMP in dma-mapping that brought the problem in the driver to
> light.
> 
> I already said the other day that cnic has been doing this for 14
> years. I'm not blaming you or your __GFP_COMP cleanup commits, they
> just uncovered that cnic was doing something wrong. My apologies if
> you took it that way.

As these devices aren't being made anymore, and this api is really not a
good idea in the first place, why don't we just leave it broken and see
if anyone notices?

thanks,

greg k-h