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

[John Garry]

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