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Message-ID: <ead14a91ffaec7b9e818edf735dbc18510d7915e.camel@linux.ibm.com>
Subject: Re: [PATCH net v3] net/mlx5: fix calling mlx5_cmd_init() before DMA
 mask is set
From:   Niklas Schnelle <schnelle@linux.ibm.com>
To:     Saeed Mahameed <saeed@kernel.org>
Cc:     Saeed Mahameed <saeedm@nvidia.com>,
        Leon Romanovsky <leon@kernel.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Matthew Rosato <mjrosato@linux.ibm.com>,
        Joerg Roedel <joro@8bytes.org>,
        Robin Murphy <robin.murphy@arm.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, Shay Drory <shayd@nvidia.com>,
        Moshe Shemesh <moshe@nvidia.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        linux-s390@vger.kernel.org, netdev@vger.kernel.org,
        linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jacob Keller <jacob.e.keller@intel.com>
Date:   Thu, 12 Oct 2023 13:39:49 +0200
In-Reply-To: <5e7ec86d690ec5337052742ca75ad2ade23f291e.camel@linux.ibm.com>
References: <20231011-mlx5_init_fix-v3-1-787ffb9183c6@linux.ibm.com>
         <ZSbnUlJT1u3xUIqY@x130> <ZSbvxeLKS8zHltdg@x130>
         <5e7ec86d690ec5337052742ca75ad2ade23f291e.camel@linux.ibm.com>
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On Thu, 2023-10-12 at 12:53 +0200, Niklas Schnelle wrote:
> On Wed, 2023-10-11 at 11:56 -0700, Saeed Mahameed wrote:
> > On 11 Oct 11:20, Saeed Mahameed wrote:
> > > On 11 Oct 09:57, Niklas Schnelle wrote:
> > > > Since commit 06cd555f73ca ("net/mlx5: split mlx5_cmd_init() to prob=
e and
> > > > reload routines") mlx5_cmd_init() is called in mlx5_mdev_init() whi=
ch is
> > > > called in probe_one() before mlx5_pci_init(). This is a problem bec=
ause
> > > > mlx5_pci_init() is where the DMA and coherent mask is set but
> > > > mlx5_cmd_init() already does a dma_alloc_coherent(). Thus a DMA
> > > > allocation is done during probe before the correct mask is set. This
> > > > causes probe to fail initialization of the cmdif SW structs on s390x
> > > > after that is converted to the common dma-iommu code. This is becau=
se on
> > > > s390x DMA addresses below 4 GiB are reserved on current machines and
> > > > unlike the old s390x specific DMA API implementation common code
> > > > enforces DMA masks.
> > > >=20
> > > > Fix this by moving set_dma_caps() out of mlx5_pci_init() and into
> > > > probe_one() before mlx5_mdev_init(). To match the overall naming sc=
heme
> > > > rename it to mlx5_dma_init().
> > >=20
> > > How about we just call mlx5_pci_init() before mlx5_mdev_init(), inste=
ad of
> > > breaking it apart ?
> >=20
> > I just posted this RFC patch [1]:
>=20
> This patch works to solve the problem as well.
>=20
> >=20
> > I am working in very limited conditions these days, and I don't have st=
rong
> > opinion on which approach to take, Leon, Niklas, please advise.
> >=20
> > The three possible solutions:
> >=20
> > 1) mlx5_pci_init() before mlx5_mdev_init(), I don't think enabling pci
> > before initializing cmd dma would be a problem.
> >=20
> > 2) This patch.
> >=20
> > 3) Shay's patch from the link below:
> > [1] https://patchwork.kernel.org/project/netdevbpf/patch/20231011184511=
.19818-1-saeed@kernel.org/
> >=20
> > Thanks,
> > Saeed.
>=20
> My first gut feeling was option 1) but I'm just as happy with 2) or 3).
> For me option 2 is the least invasive but not by much.
>=20
> For me the important thing is what Jason also said yesterday. We need
> to merge something now to unbreak linux-next on s390x and to make sure
> we don't end up with a broken v6.7-rc1. This is already hampering our
> CI tests with linux-next. So let's do whatever can be merged the
> quickest and then feel free to do any refactoring ideas that this
> discussion might have spawned on top of that. My guess for this
> criteria would be 2).
>=20
> Thanks,
> Niklas
>=20

Looking closer at the patch from Shay I do like that it changes the
order in the disable/tear down path too. So since that also fixes a PPC
issue I guess that may indeed be the best solution if we can get it
merged quickly. I'll comment with my Tested-by there too.

Thanks,
Niklas