Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 950B3486BA9 for ; Tue, 4 Aug 2026 17:05:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785863116; cv=none; b=PzoGJl5kd/b0gWZi8Q04cOuvQgu6A5/e110515aQmbvGGdMEjiZTpynRBXiV5XqeJbZ1QRPLr/L0XGRcuE4tXJUP+213INxJqObjcdDFe6+eMqCDbALkPG2NR3b1C2etMDVI8OQybW1DyFoO3Oi4ee6gyLO0dP5RcYTlrHpVA6I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785863116; c=relaxed/simple; bh=IIPV+uK9RzIxM4qreYDUAaEKrit9xi6m9STGo+r87Q0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OI9LlR+G6BBcWqrifo4ByW6P6uIWGeU6J8LUb7yGkHbjrUEoJH18jU5IUo+TZZSTbxtkk8H4TAxvFkIRhMc55EpalzaL0/4SYCgWfimUJkYazfcqlUG86UWc2Nryc8kR3o1YR9gswsqeX2AuRff7LxzTe6iHeE+OmVeu8ndjiuo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nhk5V3wk; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nhk5V3wk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E8721F000E9; Tue, 4 Aug 2026 17:05:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785863107; bh=YDEfVs0Bi8dTQeWZgvTkiOBxm/ntA3Pj+qKWpGUZhAA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=nhk5V3wkrUDVAWtxPRfrQm3EDSC20ZGWnFbzLCdVbKHLe/kjkLcRVxXiLC/fpqmuT s6oz3TO5LyY54d2/8z3wG2yq1YsXkfUjM7RBP/waiT3/rOvVyIZtbC1EaHLzgih/JQ gCk5ghpFp3q4QJF1UfpTsjMr2MPiKTxtMnVsaUSGQCThWNj03urvT1yTYKe/FFSYOq y8yn1/WasyUfVRfZ65K/xeWPp2lS1Uhrk9AV4iczW2Zub9+WHrkObkv6unPBpqWPr/ HeAJHGLUqzCJroT6mK1il32ogZzOLpWkj5eSi/upLIwHqTyE8sJtp2+KRKyZDhia0k NPoyi3CVzMuBA== Message-ID: <556894de-2e06-424b-9414-36fb0ecd9657@kernel.org> Date: Tue, 4 Aug 2026 19:05:02 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Fix incorrect flush address in direct page table reclaim To: Andy Lutomirski Cc: Qi Zheng , luto@kernel.org, linux-mm@kvack.org, Liam Howlett , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , Andrew Morton , stable@vger.kernel.org References: <3d3aa670-76bc-4df3-9c36-609c14354e9e@kernel.org> <0B39A63B-3697-4FEC-B6FF-2F4D5901F7E9@amacapital.net> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/4/26 15:43, Andy Lutomirski wrote: > >> On Aug 4, 2026, at 2:34 AM, David Hildenbrand (Arm) wrote: >> >> On 8/4/26 11:25, Qi Zheng wrote: >>> >>> >>> >>> We backported the PT_RECLAIM to our internal tree a while ago (excluding >>> the rework patch being fixed here), and it has been running stably ever >>> since. >> >> I'm wondering whether we should have a selftest that triggers this exact scenario: >> >> (a) Populate page table(s) >> (b) MADV_DONTNEED to reclaim the page table(s) >> (c) Allocate plenty of pages for another purpose (draining PCP where the page >> table likely ended up) and fill them with some data that looks like present page >> table entries. >> (d) Re-access the reclaimed VA space, expecting re-population of anonymous >> pages. >> > > If you want a better chance of hitting this bug, you could try: > > - First DONTNEED the range in multiple calls so none of them reclaim the table. Not required. If MADV_DONTNEED spans the full page table we always reclaim if it is empty after MADV_DONTNEED (there are some oddities around uffd-wp handling, which wouldn't apply here). > > - Then PREFETCH the range (or use your favorite speculative read gadget or even do a real read and ignore the signal). Maybe also do this from multiple CPUs. > Not sure if that's required, but if that's required to trigger it that certainly makes it less elegant. > - Trigger reclaim Also not sure if that one would really help. > > Then do c and d. > > The result might be so specialized that it would be of dubious value. > Right, if we cannot easily trigger it then it's way to special. -- Cheers, David