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Date:   Wed, 27 Sep 2023 16:25:28 -0400
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Subject: Re: [PATCH v12 0/6] iommu/dma: s390 DMA API conversion and optimized
 IOTLB flushing
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To:     Jason Gunthorpe <jgg@ziepe.ca>,
        Niklas Schnelle <schnelle@linux.ibm.com>
Cc:     Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        Wenjia Zhang <wenjia@linux.ibm.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Gerd Bayer <gbayer@linux.ibm.com>,
        Julian Ruess <julianr@linux.ibm.com>,
        Pierre Morel <pmorel@linux.ibm.com>,
        Alexandra Winter <wintera@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
        Hector Martin <marcan@marcan.st>,
        Sven Peter <sven@svenpeter.dev>,
        Alyssa Rosenzweig <alyssa@rosenzweig.io>,
        David Woodhouse <dwmw2@infradead.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        Yong Wu <yong.wu@mediatek.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
        Orson Zhai <orsonzhai@gmail.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Chunyan Zhang <zhang.lyra@gmail.com>,
        Chen-Yu Tsai <wens@csie.org>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Samuel Holland <samuel@sholland.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Krishna Reddy <vdumpa@nvidia.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Jonathan Corbet <corbet@lwn.net>, linux-s390@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        iommu@lists.linux.dev, asahi@lists.linux.dev,
        linux-arm-kernel@lists.infradead.org,
        linux-arm-msm@vger.kernel.org, linux-mediatek@lists.infradead.org,
        linux-sunxi@lists.linux.dev, linux-tegra@vger.kernel.org,
        linux-doc@vger.kernel.org
References: <20230825-dma_iommu-v12-0-4134455994a7@linux.ibm.com>
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 <b06a14de270a63050b0d027c24b333dba25001a4.camel@linux.ibm.com>
 <e1efbbd827e34800bd7fb0ea687645cc6c65e1ab.camel@linux.ibm.com>
 <6dab29f58ac1ccd58caaee031f98f4d0d382cbcd.camel@linux.ibm.com>
 <a672b6b122c7a5f708614346885c190a6960aaea.camel@linux.ibm.com>
 <20230927154009.GN13795@ziepe.ca>
From:   Matthew Rosato <mjrosato@linux.ibm.com>
In-Reply-To: <20230927154009.GN13795@ziepe.ca>
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On 9/27/23 11:40 AM, Jason Gunthorpe wrote:
> On Wed, Sep 27, 2023 at 05:24:20PM +0200, Niklas Schnelle wrote:
> 
>> Ok, another update. On trying it out again this problem actually also
>> occurs when applying this v12 on top of v6.6-rc3 too. Also I guess
>> unlike my prior thinking it probably doesn't occur with
>> iommu.forcedac=1 since that still allows IOVAs below 4 GiB and we might
>> be the only ones who don't support those. From my point of view this
>> sounds like a mlx5_core issue they really should call
>> dma_set_mask_and_coherent() before their first call to
>> dma_alloc_coherent() not after. So I guess I'll send a v13 of this
>> series rebased on iommu/core and with an additional mlx5 patch and then
>> let's hope we can get that merged in a way that doesn't leave us with
>> broken ConnectX VFs for too long.
> 
> Yes, OK. It definitely sounds wrong that mlx5 is doing dma allocations before
> setting it's dma_set_mask_and_coherent(). Please link to this thread
> and we can get Leon or Saeed to ack it for Joerg.
> 

Hi Niklas,

I bisected the start of this issue to the following commit (only noticeable on s390 when you apply this subject series on top):

06cd555f73caec515a14d42ef052221fa2587ff9 ("net/mlx5: split mlx5_cmd_init() to probe and reload routines")

Which went in during the merge window.  Please include with your fix and/or report to the mlx5 maintainers.  Looks like the changes in this patch match what you and Jason describe; it splits up mlx5_cmd_init() and moves part of the call earlier.  The net result is we first call mlx5_mdev_init>mlx5_cmd_init->alloc_cmd_page->dma_alloc_coherent and then sometime later call mlx5_pci_init->set_dma_caps->dma_set_mask_and_coherent. 

Prior to this patch, we would not drive mlx5_cmd_init (and thus that first dma_alloc_coherent) until mlx5_init_one which happens _after_ mlx5_pci_init->set_dma_caps->dma_set_mask_and_coherent.

Thanks,
Matt