From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oa1-f52.google.com (mail-oa1-f52.google.com [209.85.160.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2C4DB28504F for ; Tue, 21 Apr 2026 16:05:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.160.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776787560; cv=none; b=j/aTzfcOkZDzAlOGXSwOp7fuFVqnP/4nho9dlw5xbSUqSQl5JBFa+uVdcF5VySW+QnhSkwSriYTnOvkMb7dZ8haYrD4C/y8i2ymWR2L4BdIkIft3p/S2Rh9iwCwYNB/60AJ8kjoLc8rNZwbmfLSN3aGQAXGDhYbo1c6MMxbbHTw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776787560; c=relaxed/simple; bh=jAY4keg8FJfNurmuX9nJjOlENNYFl0V76Uqim8ZxTL8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=H5oBWEYh1Yz6Kfhk+z57AruO3wPNza0Fu5JOwEdo5HlL7C4eXaSoM4EQDHdPd1/l7e33SZdgGHiZyUMqvtIbaFOP+QpRIa6Md/H4Tvt4XzBW8Li1ZmaBnWSv7/IrOEnxmJwTLTGOqJHUBBCu5YkgUVOOhlwwXqaVCWVQA8L6Vds= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.dk; spf=pass smtp.mailfrom=kernel.dk; dkim=pass (2048-bit key) header.d=kernel-dk.20251104.gappssmtp.com header.i=@kernel-dk.20251104.gappssmtp.com header.b=B+HSde7G; arc=none smtp.client-ip=209.85.160.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.dk Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=kernel.dk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20251104.gappssmtp.com header.i=@kernel-dk.20251104.gappssmtp.com header.b="B+HSde7G" Received: by mail-oa1-f52.google.com with SMTP id 586e51a60fabf-41708f6c3feso2851922fac.3 for ; Tue, 21 Apr 2026 09:05:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20251104.gappssmtp.com; s=20251104; t=1776787557; x=1777392357; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=KE8Zb2alx5YyGRI4wpRGEaceVt7UtJzgNhyIfugfLzg=; b=B+HSde7G04Fj0qPHLo5KVoCYqZLsC9AztWMP2qmkhMA8fktTd5Kq5IZJgBGFaBrZZd OnhnrE6H6HSv4nTMFwPZKUKD0cx2cG5WIxLfgntZBUcvTpwO3YDFDudReqBoeMIe4VEy w+1C6kzJKFd5y/AM0KGup/krSQJe0uvBZgEnSXwlfp2ii5k004SmFJo9NUku8Puu+QgY nONFfT2ZK1s6as5n1R291+OpXowmZ+o9qHjOSh0juvc/tD3eKrt+4O/axpOvAqDijcKR Lqy6MA83GxhJvZk8rZYX46Y6i04Qku/jnxJSrZoMy8NmiUDVC2uPOCNB3HTS7vyvlcep D/2g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776787557; x=1777392357; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=KE8Zb2alx5YyGRI4wpRGEaceVt7UtJzgNhyIfugfLzg=; b=PNVse36qP0fzISwgSn9LapUfbStL+Nv4b750/PXEPVVevSZOT7o0/OAt1cR4Hc/f3x Z0OXDtAJLFOEMpzg3RGKG0gKKw6V+sA138aZfkR6pMeHAcSJxflmz12kb5GUynuahOZc HbHXeJSdGl29QMhLg3GSdnVRoKBqso/IYdSE+kekOzt6itGO4G8MuJwwmE8S5DC6MZdC 6ap0pzOhlBK9GZcdPWcRHnotgiQJbu8zO8joPNXbd14CXlgcEulrEO9jOr2Ev6OLiyyT rvqZAxRRz7fLAvk4S8QKOM7hqE/H16X2M9z/g8Yxu19J4GPx6SLmXwYgAWG+MSKIFMio JOmQ== X-Gm-Message-State: AOJu0YxjpRyD5HIqLJ4rxnvQd2kHVVDczA8UykZKyQ5qg+WMGXYlNwIU JS7kN/gThrLuk+XM4hHeJV7TuW+Hzkpd+LKUQ/YcjNjuZyLntFq99t9v6UvsJv5bsdm35nl35IY uoe9aJlw= X-Gm-Gg: AeBDieuIrR7AeuWCNPIaKOyGtr59aDXIidxdL/W8lBV77kCHJMZSzE+3QId5AK8tPrT Jlwqj+5akdVE6+ahRFn1YOn416IXXp0m98Wx1iJgbAzdehEfvq7DotbG3lAR1pvfeNyb+bxAhIS kWsgItQVHJfv4cP128m3wUTn2HoPM0SxQ6dZqnb7XqdF8SUML442LVPOZg4NsU0augEI/fXDIjV qEkutfAW06fCx325FCs/ILQCZYBN1ZB6isN6tqruP+L5JUMb9heoqYnEgtpb6cTU+sAKtA74lJR 7aWAq9gzHxgqM3CVrjfAdUgZq0v5i1LzGaFNVA/exEXmHBsDnfM8nm+U9eo92QKaAzUoPdCQD7/ /7+E9r56PFF/AUHWZjAfeuUZgpOAx7YjaBdZh72EGJmQCpUGKmccZ7T32rdoz1N0UonsB3/sg8K 5+vA+s9zGiSa5FuIGM7XdrnGIzaFNCiSHB6vRsXFRjJUDyd1Z3uCI5+1qLC+F0xBfqpJeY9KMAi jyfrTigrUW2Du2kfh88lCdwlBtDhw== X-Received: by 2002:a05:6870:b016:b0:417:49da:7ff8 with SMTP id 586e51a60fabf-42adeda9c9cmr10737156fac.34.1776787556662; Tue, 21 Apr 2026 09:05:56 -0700 (PDT) Received: from [192.168.1.102] ([96.43.243.2]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-42b934a2e8esm12603931fac.10.2026.04.21.09.05.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Apr 2026 09:05:55 -0700 (PDT) Message-ID: Date: Tue, 21 Apr 2026 10:05:54 -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 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 From: Jens Axboe In-Reply-To: <2026042140-arrogance-freehand-d8bd@gregkh> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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 ;-) -- Jens Axboe