netdev - Re: [PATCH net v3] net/mlx5: fix calling mlx5_cmd

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Message-ID: <ZSbvxeLKS8zHltdg@x130>
Date: Wed, 11 Oct 2023 11:56:05 -0700
From: Saeed Mahameed <saeed@...nel.org>
To: Niklas Schnelle <schnelle@...ux.ibm.com>
Cc: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Matthew Rosato <mjrosato@...ux.ibm.com>,
	Joerg Roedel <joro@...tes.org>, 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,
	Jacob Keller <jacob.e.keller@...el.com>
Subject: Re: [PATCH net v3] net/mlx5: fix calling mlx5_cmd_init() before DMA
 mask is set

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 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().
>
>How about we just call mlx5_pci_init() before mlx5_mdev_init(), instead of
>breaking it apart ?

I just posted this RFC patch [1]:

I am working in very limited conditions these days, and I don't have strong
opinion on which approach to take, Leon, Niklas, please advise.

The three possible solutions:

1) mlx5_pci_init() before mlx5_mdev_init(), I don't think enabling pci
before initializing cmd dma would be a problem.

2) This patch.

3) Shay's patch from the link below:
[1] https://patchwork.kernel.org/project/netdevbpf/patch/20231011184511.19818-1-saeed@kernel.org/

Thanks,
Saeed.