linux-kernel - Re: arm64 iommu groups issue

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Date:   Mon, 4 Nov 2019 12:18:01 +0000
From:   John Garry <john.garry@...wei.com>
To:     Robin Murphy <robin.murphy@....com>, Marc Zyngier <maz@...nel.org>,
        "Will Deacon" <will@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        "Guohanjun (Hanjun Guo)" <guohanjun@...wei.com>
CC:     iommu <iommu@...ts.linux-foundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linuxarm <linuxarm@...wei.com>,
        Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Saravana Kannan" <saravanak@...gle.com>
Subject: Re: arm64 iommu groups issue

+

On 19/09/2019 15:35, John Garry wrote:
> On 19/09/2019 14:25, Robin Murphy wrote:
>>> When the port eventually probes it gets a new, separate group.
>>>
>>> This all seems to be as the built-in module init ordering is as
>>> follows: pcieport drv, smmu drv, mlx5 drv
>>>
>>> I notice that if I build the mlx5 drv as a ko and insert after boot,
>>> all functions + pcieport are in the same group:
>>>
>>> [   11.530046] hisi_sas_v2_hw HISI0162:01: Adding to iommu group 0
>>> [   17.301093] hns_dsaf HISI00B2:00: Adding to iommu group 1
>>> [   18.743600] ehci-platform PNP0D20:00: Adding to iommu group 2
>>> [   20.212284] pcieport 0002:f8:00.0: Adding to iommu group 3
>>> [   20.356303] pcieport 0004:88:00.0: Adding to iommu group 4
>>> [   20.493337] pcieport 0005:78:00.0: Adding to iommu group 5
>>> [   20.702999] pcieport 000a:10:00.0: Adding to iommu group 6
>>> [   20.859183] pcieport 000c:20:00.0: Adding to iommu group 7
>>> [   20.996140] pcieport 000d:30:00.0: Adding to iommu group 8
>>> [   21.152637] serial 0002:f9:00.0: Adding to iommu group 3
>>> [   21.346991] serial 0002:f9:00.1: Adding to iommu group 3
>>> [  100.754306] mlx5_core 000a:11:00.0: Adding to iommu group 6
>>> [  101.420156] mlx5_core 000a:11:00.1: Adding to iommu group 6
>>> [  292.481714] mlx5_core 000a:11:00.2: Adding to iommu group 6
>>> [  293.281061] mlx5_core 000a:11:00.3: Adding to iommu group 6
>>>
>>> This does seem like a problem for arm64 platforms which don't support
>>> ACS, yet enable an SMMU. Maybe also a problem even if they do support
>>> ACS.
>>>
>>> Opinion?
>>
> 
> Hi Robin,
> 
>> Yeah, this is less than ideal.
> 
> For sure. Our production D05 boards don't ship with the SMMU enabled in 
> BIOS, but it would be slightly concerning in this regard if they did.
> 
>  > One way to bodge it might be to make
>> pci_device_group() also walk downwards to see if any non-ACS-isolated
>> children already have a group, rather than assuming that groups get
>> allocated in hierarchical order, but that's far from ideal.
> 
> Agree.
> 
> My own workaround was to hack the mentioned iort code to defer the PF 
> probe if the parent port had also yet to probe.
> 
>>
>> The underlying issue is that, for historical reasons, OF/IORT-based
>> IOMMU drivers have ended up with group allocation being tied to endpoint
>> driver probing via the dma_configure() mechanism (long story short,
>> driver probe is the only thing which can be delayed in order to wait for
>> a specific IOMMU instance to be ready).However, in the meantime, the
>> IOMMU API internals have evolved sufficiently that I think there's a way
>> to really put things right - I have the spark of an idea which I'll try
>> to sketch out ASAP...
>>
> 
> OK, great.
> 
> Thanks,
> John
> 
>> Robin.
>