linux-kernel - Re: [Patch V2 0/2] iommu/arm-smmu: Fix races in iommu domain/group creation

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Message-ID: <9c38c53c-c145-097a-4c7e-40f1c06a1f01@arm.com>
Date:   Mon, 2 Aug 2021 16:46:37 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Will Deacon <will@...nel.org>, Ashish Mhetre <amhetre@...dia.com>
Cc:     vdumpa@...dia.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [Patch V2 0/2] iommu/arm-smmu: Fix races in iommu domain/group
 creation

On 2021-08-02 16:16, Will Deacon wrote:
> On Fri, Jun 18, 2021 at 02:00:35AM +0530, Ashish Mhetre wrote:
>> Multiple iommu domains and iommu groups are getting created for the devices
>> sharing same SID. It is expected for devices sharing same SID to be in same
>> iommu group and same iommu domain.
>> This is leading to context faults when one device is accessing IOVA from
>> other device which shouldn't be the case for devices sharing same SID.
>> Fix this by protecting iommu domain and iommu group creation with mutexes.
> 
> Robin -- any chance you could take a look at these, please? You had some
> comments on the first version which convinced me that they are needed,
> but I couldn't tell whether you wanted to solve this a different way or not.

Sorry, I was lamenting that this came to light due to the 
of_iommu_configure() flow being yucky, but that wasn't meant to imply 
that there aren't - or couldn't be in future - better reasons for 
iommu_probe_device() to be robust against concurrency anyway. I do think 
these are legitimate fixes to make in their own right, even if the 
current need might get swept back under the rug in future.

I would say, however, that the commit messages seem to focus too much on 
the wrong details and aren't overly useful, and patch #2 is missing 
Ashish's sign-off.

Thanks,
Robin.