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

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Message-ID: <tf2zu6gqaii2bjipbo2mn2hz64px2624rfcmyg36rkq4bskxiw@zgjzznig6e22>
Date:   Mon, 2 Oct 2023 00:50:21 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 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.

Regards,
Jerry