Re: [PATCH] io_uring: take page references for NOMMU pbuf_ring mmaps

Jens Axboe
2026-04-21T14:02:54Z

On 4/21/26 7:55 AM, Greg Kroah-Hartman wrote:
> On Tue, Apr 21, 2026 at 07:50:32AM -0600, Jens Axboe wrote:
>> On 4/21/26 7:46 AM, Greg Kroah-Hartman wrote:
>>> Note, I have no way of testing this, I'm only forwarding this on because
>>> I got the bug report and was able to generate something that "seems"
>>
>> AI bug report I presume? Because I can't imagine anyone ever attempted
>> to run this.
>
> Yes, I got a bunch of "non-mmu" bug reports, which is a bit odd but I
> guess you can do that with qemu these days? I should dig into that,
> maybe that way I can test this and get a reproducer for you. If not,
> let's just bin the thing.

Was just pondering if I can run it in qemu. I'll take a look. But I knew
it'd be some kind of AI bs, because why else would anyone look at nommu
in the first place. But we have it in the codebase, so...

>>> correct, but it might be a total load of crap here, my knowledge of the
>>> vm layer is very low so take this for where it is coming from (i.e. a
>>> non-deterministic pattern matching system.)
>>>
>>> I do have another patch that just disables io_uring for !MMU systems, if
>>> you want that instead? Or is this feature something that !MMU devices
>>> actually care about?
>>
>> I mean, who really cares about !MMU in the first place, we should just
>> kill that off with a passion.
>>
>> Let me take a closer look at this and bounce it past some vm people, my
>> nommu knowledge is close to zero as it's never been relevant in my
>> professional life time. Which is saying something...
>
> Let me try to get a reproducer going first, let's not waste any more
> human time on this just yet, sorry for sending this out without that
> done first...

Thanks!

--
Jens Axboe