Re: WARNING: drivers/iommu/io-pgtable-arm.c:639

[Sebastian Ott <sebott@redhat.com>]

On Wed, 10 Dec 2025, Keith Busch wrote:
> On Wed, Dec 10, 2025 at 12:08:36PM +0100, Sebastian Ott wrote:
>> On Wed, 10 Dec 2025, Keith Busch wrote:
>>> On Tue, Dec 09, 2025 at 12:43:31PM +0100, Sebastian Ott wrote:
>>>> got the following warning after a kernel update on Thurstday, leading to a
>>>> panic and fs corruption. I didn't capture the first warning but I'm pretty
>>>> sure it was the same. It's reproducible but I didn't bisect since it
>>>> borked my fs. The only hint I can give is that v6.18 worked. Is this a
>>>> known issue? Anything I should try?
>>>
>>> Could you check if your nvme device supports SGLs? There are some new
>>> features in 6.19 that would allow merging IO that wouldn't have happened
>>> before. You can check from command line:
>>>
>>>  # nvme id-ctrl /dev/nvme0 | grep sgl
>>
>> # nvme id-ctrl /dev/nvme0n1 | grep sgl
>> sgls      : 0xf0002
>
> Oh neat, so you *do* support SGL. Not that it was required as arm64
> can support iommu granularities larger than the NVMe PRP unit, so the
> bug was possible to hit in either case for you (assuming the smmu was
> configured with 64k io page size).
>
> Anyway, thanks for the report, and sorry for the fs trouble the bug
> caused you.

No worries, it was a test system in need for an upgrade anyway.
Thanks for the quick fix!

> I'm working on a blktest to specifically target this
> condition so we don't regress again. I just need to make sure to run it
> on a system with iommu enabled (usually it's off on my test machine).

Great!