linux-kernel - Re: [PATCH net v2] net/mlx5: fix calling mlx5_cmd

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Date:   Wed, 04 Oct 2023 14:40:49 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Leon Romanovsky <leon@...nel.org>, Joerg Roedel <joro@...tes.org>
Cc:     Saeed Mahameed <saeedm@...dia.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Robin Murphy <robin.murphy@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Shay Drory <shayd@...dia.com>,
        Moshe Shemesh <moshe@...dia.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] net/mlx5: fix calling mlx5_cmd_init() before DMA
 mask is set

On Sat, 2023-09-30 at 10:36 +0300, Leon Romanovsky wrote:
> On Fri, Sep 29, 2023 at 02:15:49PM +0200, Niklas Schnelle wrote:
> > Since commit 06cd555f73ca ("net/mlx5: split mlx5_cmd_init() to probe and
> > reload routines") mlx5_cmd_init() is called in mlx5_mdev_init() which is
> > called in probe_one() before mlx5_pci_init(). This is a problem because
> > 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 because 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.
> > 
> > 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 scheme
> > rename it to mlx5_dma_init().
> > 
> > Link: https://lore.kernel.org/linux-iommu/cfc9e9128ed5571d2e36421e347301057662a09e.camel@linux.ibm.com/
> > Fixes: 06cd555f73ca ("net/mlx5: split mlx5_cmd_init() to probe and reload routines")
> > Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> > ---
> > Note: I ran into this while testing the linked series for converting
> > s390x to use dma-iommu. The existing s390x specific DMA API
> > implementation doesn't respect DMA masks and is thus not affected
> > despite of course also only supporting DMA addresses above 4 GiB.
> > ---
> > Changes in v2:
> > - Instead of moving the whole mlx5_pci_init() only move the
> >   set_dma_caps() call so as to keep pci_enable_device() after the FW
> >   command interface initialization (Leon)
> > - Link to v1: https://lore.kernel.org/r/20230928-mlx5_init_fix-v1-1-79749d45ce60@linux.ibm.com
> > ---
> >  drivers/net/ethernet/mellanox/mlx5/core/main.c | 18 +++++++++---------
> >  1 file changed, 9 insertions(+), 9 deletions(-)
> > 
> 
> Thanks,
> Reviewed-by: Leon Romanovsky <leonro@...dia.com>

Thank you for the review. Assuming the mlx5 tree is included in linux-
next I think it would be easiest if this goes via that tree thereby
unbreaking linux-next for s390. Or do you prefer Joerg to take this via
the IOMMU tree or even some other tree?

Thanks,
Niklas