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Tue, 21 Apr 2026 09:21:05 -0700 (PDT) Received: from [192.168.1.102] ([96.43.243.2]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-7dccfe912edsm3490231a34.16.2026.04.21.09.21.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Apr 2026 09:21:05 -0700 (PDT) Message-ID: Date: Tue, 21 Apr 2026 10:21:04 -0600 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] io_uring: take page references for NOMMU pbuf_ring mmaps From: Jens Axboe To: Greg Kroah-Hartman Cc: io-uring@vger.kernel.org References: <2026042115-body-attention-d15b@gregkh> <842a9dff-b12c-4cec-bc8d-8c1adb3ba280@kernel.dk> <2026042108-fiscally-unglazed-56c7@gregkh> <2026042140-arrogance-freehand-d8bd@gregkh> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/21/26 10:05 AM, Jens Axboe wrote: > On 4/21/26 10:01 AM, Greg Kroah-Hartman wrote: >> On Tue, Apr 21, 2026 at 03:55:38PM +0200, 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. >>> >>>>> 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... >> >> Ok, attached is a poc.c and a script to run it. If you run this on a >> 7.0 kernel today, it "should" crash. and then if you apply the patch it >> doesn't (or at least that's what happened in my testing.) >> >> Note, I have run this locally, and it seems to work, but be careful, I >> can't guarantee anything, it does seem quite odd in that it "crashes" >> the kernel with a sysrq call to show "proof". Although that is a cool >> trick, I need to remember that... > > I'll try and run a nommu qemu and see what pops out on my end. What a > waste of time for a nothing burger ;-) What is fix-paddr.py? It's referenced in the build script. -- Jens Axboe