Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.36 as permitted sender) client-ip=23.128.96.36;
Message-ID: <2554ed057e08e66dd110c3e09a27378b9a06bdd6.camel@redhat.com>
Subject: Re: [PATCH 3/3] cnic,bnx2,bnx2x: use UIO_MEM_DMA_COHERENT
From:   Paolo Abeni <pabeni@redhat.com>
To:     Hannes Reinecke <hare@suse.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jerry Snitselaar <jsnitsel@redhat.com>
Cc:     Christoph Hellwig <hch@lst.de>, Chris Leech <cleech@redhat.com>,
        Rasesh Mody <rmody@marvell.com>,
        Ariel Elior <aelior@marvell.com>,
        Sudarsana Kalluru <skalluru@marvell.com>,
        Manish Chopra <manishc@marvell.com>,
        Nilesh Javali <njavali@marvell.com>,
        Manish Rangankar <mrangankar@marvell.com>,
        John Meneghini <jmeneghi@redhat.com>,
        Lee Duncan <lduncan@suse.com>,
        Mike Christie <michael.christie@oracle.com>,
        Hannes Reinecke <hare@kernel.org>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Thu, 05 Oct 2023 12:39:05 +0200
In-Reply-To: <0e0040be-0375-4461-914d-1ea9d04ee62c@suse.de>
References: <20230929170023.1020032-1-cleech@redhat.com>
         <20230929170023.1020032-4-cleech@redhat.com>
         <2023093055-gotten-astronomy-a98b@gregkh>
         <ZRhmqBRNUB3AfLv/@rhel-developer-toolbox>
         <2023093002-unlighted-ragged-c6e1@gregkh>
         <e0360d8f-6d36-4178-9069-d633d9b7031d@suse.de>
         <2023100114-flatware-mourner-3fed@gregkh>
         <7pq4ptas5wpcxd3v4p7iwvgoj7vrpta6aqfppqmuoccpk4mg5t@fwxm3apjkez3>
         <20231002060424.GA781@lst.de>
         <tf2zu6gqaii2bjipbo2mn2hz64px2624rfcmyg36rkq4bskxiw@zgjzznig6e22>
         <2023100233-salsa-joyous-6d8c@gregkh>
         <0e0040be-0375-4461-914d-1ea9d04ee62c@suse.de>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.46.4 (3.46.4-1.fc37) 
MIME-Version: 1.0
Precedence: bulk

On Mon, 2023-10-02 at 10:59 +0200, Hannes Reinecke wrote:
> On 10/2/23 10:46, Greg Kroah-Hartman wrote:
> > 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 f=
or
> > > > > 6.2):
> > > >=20
> > > > 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 j=
ust
> > > > happened to accidentally work the trivial dma coherent allocator th=
at
> > > > is used on x86.
> > > >=20
> > >=20
> > > re-sending since gmail decided to not send plain text:
> > >=20
> > > 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.
> > >=20
> > > 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.
> >=20
> > 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?
> >=20
> Guess what triggered this mail thread.
> Some customers did notice.
>=20
> Problem is that these devices were built as the network interface in=20
> some bladecenter machines, so you can't just replace them with a=20
> different Ethernet card.

This route looks a no-go.

Out of sheer ignorance, would the iommu hack hinted in the cover letter
require similar controversial changes?

Cheers,

Paolo