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

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Message-ID: <ZSgk8huR9xCUHWBi@x130>
Date:   Thu, 12 Oct 2023 09:55:14 -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 12 Oct 13:39, Niklas Schnelle wrote:
>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 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]:
>>
>> This patch works to solve the problem as well.
>>
>> >
>> > 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.
>>
>> 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.
>>
>> 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).
>>
>> Thanks,
>> Niklas
>>
>
>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.
>

Ack, will take Shay's patch then, Will add your Test-by and 
Reviewed-by.

>Thanks,
>Niklas