linux-kernel - Re: [PATCH v2 6/9] Revert "iommu/arm-smmu: Make arm-smmu-v3 explicitly non-modular"

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Date:   Fri, 8 Nov 2019 18:00:52 +0000
From:   John Garry <john.garry@...wei.com>
To:     Will Deacon <will@...nel.org>
CC:     <iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>,
        "Isaac J. Manjarres" <isaacm@...eaurora.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Saravana Kannan <saravanak@...gle.com>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v2 6/9] Revert "iommu/arm-smmu: Make arm-smmu-v3
 explicitly non-modular"

On 08/11/2019 17:48, Will Deacon wrote:
> On Fri, Nov 08, 2019 at 05:32:48PM +0000, Will Deacon wrote:
>> On Fri, Nov 08, 2019 at 05:25:09PM +0000, John Garry wrote:
>>> On 08/11/2019 16:47, Will Deacon wrote:
>>>> On Fri, Nov 08, 2019 at 04:44:25PM +0000, John Garry wrote:
>>>>> BTW, it now looks like it was your v1 series I was testing there, on your
>>>>> branch iommu/module. It would be helpful to update for ease of testing.
>>>>
>>>> Yes, sorry about that. I'll update it now (although I'm not sure it will
>>>> help with this -- I was going to see what happens with other devices such
>>>> as the intel-iommu or storage controllers)
>>>
>>> So I tried your v2 series for this - it has the same issue, as I
>>> anticipated.
>>
>> Right, I'm just not sure how resilient drivers are expected to be to force
>> unbinding like this. You can break lots of stuff with root...
>>
>>> It seems that some iommu drivers do call iommu_device_register(), so maybe a
>>> decent reference. Or simply stop the driver being unbound.
>>
>> I'm not sure what you mean about iommu_device_register() (we call that
>> already), but I guess we can keep the '.suppress_bind_attrs = true' if
>> necessary. I'll have a play on my laptop and see how well that works if
>> you start unbinding stuff.
> 
> So unbinding the nvme driver goes bang:
> 
> [90139.090158] nvme nvme0: failed to set APST feature (-19)
> [90141.966780] Aborting journal on device dm-1-8.
> [90141.967124] Buffer I/O error on dev dm-1, logical block 26247168, lost sync page write
> [90141.967169] JBD2: Error -5 detected when updating journal superblock for dm-1-8.
> [90141.967403] Buffer I/O error on dev dm-1, logical block 0, lost sync page write
> [90141.967454] EXT4-fs (dm-1): I/O error while writing superblock
> [90141.967467] EXT4-fs error (device dm-1): ext4_journal_check_start:61: Detected aborted journal
> [90141.967473] EXT4-fs (dm-1): Remounting filesystem read-only
> [90141.967569] Buffer I/O error on dev dm-1, logical block 0, lost sync page write
> [90141.967682] EXT4-fs (dm-1): I/O error while writing superblock
> 
> and I've not managed to recover the thing yet (it's stuck trying to reboot.)
> 

Not surprised. I guess the device backing your root directory disappeared.

> What state was your system in after unbinding the SMMU?

Unusable again. For me the storage controller backing the root directory 
is compromised by disabling the SMMU unsafely.

Thanks,
John