linux-kernel - Re: [PATCH v3 3/4] scsi: core: Cap shost max_sectors according to DMA optimum mapping limits

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Date:   Fri, 10 Jun 2022 16:37:54 +0100
From:   John Garry <john.garry@...wei.com>
To:     Bart Van Assche <bvanassche@....org>,
        <damien.lemoal@...nsource.wdc.com>, <joro@...tes.org>,
        <will@...nel.org>, <jejb@...ux.ibm.com>,
        <martin.petersen@...cle.com>, <hch@....de>,
        <m.szyprowski@...sung.com>, <robin.murphy@....com>
CC:     <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-ide@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
        <linux-scsi@...r.kernel.org>, <liyihang6@...ilicon.com>,
        <chenxiang66@...ilicon.com>, <thunder.leizhen@...wei.com>
Subject: Re: [PATCH v3 3/4] scsi: core: Cap shost max_sectors according to DMA
 optimum mapping limits

On 09/06/2022 21:34, Bart Van Assche wrote:
> On 6/9/22 10:54, John Garry wrote:
>> ok, but do you have a system where the UFS host controller is behind 
>> an IOMMU? I had the impression that UFS controllers would be mostly 
>> found in embedded systems and IOMMUs are not as common on there.
> 
> Modern phones have an IOMMU. Below one can find an example from a Pixel 
> 6 phone. The UFS storage controller is not controller by the IOMMU as 
> far as I can see but I wouldn't be surprised if the security team would 
> ask us one day to enable the IOMMU for the UFS controller.

OK, then unfortunately it seems that you have no method to test. I might 
be able to test USB MSC but I am not even sure if I can even get DMA 
mappings who length exceeds the IOVA rcache limit there.

Thanks,
John