From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6507EC64EC4 for ; Wed, 22 Feb 2023 11:48:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231144AbjBVLsc (ORCPT ); Wed, 22 Feb 2023 06:48:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36774 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231551AbjBVLs2 (ORCPT ); Wed, 22 Feb 2023 06:48:28 -0500 Received: from mail-ed1-x52c.google.com (mail-ed1-x52c.google.com [IPv6:2a00:1450:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59FA334038 for ; Wed, 22 Feb 2023 03:48:27 -0800 (PST) Received: by mail-ed1-x52c.google.com with SMTP id ee7so14140227edb.2 for ; Wed, 22 Feb 2023 03:48:27 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=u0SkOKRxQb31uA959ab+LjFmT74FnfTe8YzbdQveaiY=; b=UqDS+6tqNYyjqohkN0RYnKWLUOdzlgyc8hyv0ooxuSLy2PIILQb1K4desrZLIb09DP MZVlPweGs4gOkRLk8WL/QYenJ4HLb3H7CtMPHKaTcuBXkzLmXH1Qa+wDP0wsqhAcRzco r1K2i0iPhcZbgToPRI4vyBH6sO8JggrUXhuS5ISy03nEazNH9t/MQRFYmU7lkHV2E0rL KoOgG2YEoYcAptDBxjJCyy1TDAo8OXHo/Q/mPZ7YncRmGQL/quWx3FlKCvlr8IZ/2oCX OjsCCtkkOKtFrAR6GvA//DLeDNTUotumhmaBWsa2KXYn9wcuEvePHKi20W1yQXRLwOiv tGbg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=u0SkOKRxQb31uA959ab+LjFmT74FnfTe8YzbdQveaiY=; b=Ik6pfugocaJMPLRzNzDjmcqTBdPaBBEU7iDPNXYH/mHO8iDASvoe/531/umfzmBfpe X74w6Q7qxzIFy6KLhRm9Sn7lRvN1AYg6bJ9KrMmNgA9TDEXORzIaSGThRE6viIb5G3Lm nAGqIGTTscA0qMjF2bLVg8bwS7VUxUERb4bDE3eTuZ7Iq9zEIAaHn//m7g7zKFK5r0Zk FThy4koOQ57NO8zrXInHdSeeAJcO3EO80oDVpLT66nosZdjlt2be9qkx0GKt6tgw4DLT ZseGC0Wqj2zGvP95dbkiTac+kIHag/Q3lsoAMn+5AIkD1APp1pF+rh6Isdb2iAXDOVRN 5/DA== X-Gm-Message-State: AO0yUKXMnH4k5fRu3eNjRuVoanHvrnuUhZMZ0OjE9LXomwJzykOXj/OU 64D9z7qd6JKXRdH69xVhZAPDAltuPV5hy5oTatVL7w== X-Google-Smtp-Source: AK7set+7jDBY525NdRoBeszWKhBVRicR26iUfAdJlIK3aE5RKh3n+8X38UCVRCGGxqOdSWAvqZonp5dnF09jL/p8IDM= X-Received: by 2002:a17:906:eb4d:b0:87b:dce7:c245 with SMTP id mc13-20020a170906eb4d00b0087bdce7c245mr7249278ejb.3.1677066505580; Wed, 22 Feb 2023 03:48:25 -0800 (PST) MIME-Version: 1.0 References: <20230202112915.867409-1-usama.anjum@collabora.com> <20230202112915.867409-4-usama.anjum@collabora.com> <36ddfd75-5c58-197b-16c9-9f819099ea6d@collabora.com> <6d2b40c6-bed9-69a6-e198-537b50953acd@collabora.com> In-Reply-To: From: =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= Date: Wed, 22 Feb 2023 12:48:13 +0100 Message-ID: Subject: Re: [PATCH v10 3/6] fs/proc/task_mmu: Implement IOCTL to get and/or the clear info about PTEs To: Muhammad Usama Anjum Cc: Andrei Vagin , Mike Rapoport , Nadav Amit , David Hildenbrand , Andrew Morton , Paul Gofman , Cyrill Gorcunov , Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Peter Xu , Matthew Wilcox , Pasha Tatashin , Axel Rasmussen , "Gustavo A . R . Silva" , Dan Williams , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Greg KH , kernel@collabora.com, Danylo Mocherniuk Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 Feb 2023 at 12:06, Muhammad Usama Anjum wrote: > > On 2/22/23 3:44=E2=80=AFPM, Micha=C5=82 Miros=C5=82aw wrote: > > On Wed, 22 Feb 2023 at 11:11, Muhammad Usama Anjum > > wrote: > >> On 2/21/23 5:42=E2=80=AFPM, Micha=C5=82 Miros=C5=82aw wrote: > >>> On Tue, 21 Feb 2023 at 11:28, Muhammad Usama Anjum > >>> wrote: > >>>> > >>>> Hi Micha=C5=82, > >>>> > >>>> Thank you so much for comment! > >>>> > >>>> On 2/17/23 8:18=E2=80=AFPM, Micha=C5=82 Miros=C5=82aw wrote: > >>> [...] > >>>>> For the page-selection mechanism, currently required_mask and > >>>>> excluded_mask have conflicting > >>>> They are opposite of each other: > >>>> All the set bits in required_mask must be set for the page to be sel= ected. > >>>> All the set bits in excluded_mask must _not_ be set for the page to = be > >>>> selected. > >>>> > >>>>> responsibilities. I suggest to rework that to: > >>>>> 1. negated_flags: page flags which are to be negated before applyin= g > >>>>> the page selection using following masks; > >>>> Sorry I'm unable to understand the negation (which is XOR?). Lets lo= ok at > >>>> the truth table: > >>>> Page Flag negated_flags > >>>> 0 0 0 > >>>> 0 1 1 > >>>> 1 0 1 > >>>> 1 1 0 > >>>> > >>>> If a page flag is 0 and negated_flag is 1, the result would be 1 whi= ch has > >>>> changed the page flag. It isn't making sense to me. Why the page fla= g bit > >>>> is being fliped? > >>>> > >>>> When Anrdei had proposed these masks, they seemed like a fancy way o= f > >>>> filtering inside kernel and it was straight forward to understand. T= hese > >>>> masks would help his use cases for CRIU. So I'd included it. Please = can you > >>>> elaborate what is the purpose of negation? > >>> > >>> The XOR is a way to invert the tested value of a flag (from positive > >>> to negative and the other way) without having the API with invalid > >>> values (with required_flags and excluded_flags you need to define a > >>> rule about what happens if a flag is present in both of the masks - > >>> either prioritise one mask over the other or reject the call). > >> At minimum, one mask (required, any or excluded) must be specified. Fo= r a > >> page to get selected, the page flags must fulfill the criterion of all= the > >> specified masks. > > > > [Please see the comment below.] > > > > [...] > >> Lets translate words into table: > > [Yes, those tables captured the intent correctly.] > > > >>> BTW, I think I assumed that both conditions (all flags in > >>> required_flags and at least one in anyof_flags is present) need to be > >>> true for the page to be selected - is this your intention? > >> All the masks are optional. If all or any of the 3 masks are specified= , the > >> page flags must pass these masks to get selected. > > > > This explanation contradicts in part the introductory paragraph, but > > this version seems more useful as you can pass all masks zero to have > > all pages selected. > Sorry, I wrote it wrongly. (All the masks are not optional.) Let me > rephrase. All or at least any 1 of the 3 masks (required, any, exclude) > must be specified. The return_mask must always be specified. Error is > returned if all 3 masks (required, anyof, exclude) are zero or return_mas= k > is zero. Why do you need those restrictions? I'd guess it is valid to request a list of all pages with zero return_mask - this will return a compact list of used ranges of the virtual address space. > >> After taking a while to understand this and compare with already prese= nt > >> flag system, `negated flags` is comparatively difficult to understand = while > >> already present flags seem easier. > > > > Maybe replacing negated_flags in the API with matched_values =3D > > ~negated_flags would make this better? > > > > We compare having to understand XOR vs having to understand ordering > > of required_flags and excluded_flags. > There is no ordering in current masks scheme. No mask is preferable. For = a > page to get selected, all the definitions of the masks must be fulfilled. > You have come up with good example that what if required_mask =3D > exclude_mask. In this case, no page will fulfill the criterion and hence = no > page would be selected. It is user's fault that he isn't understanding th= e > definitions of these masks correctly. > > Now thinking about it, I can add a error check which would return error i= f > a bit in required and excluded masks matches. Would you like it? Lets put > this check in place. > (Previously I'd left it for user's wisdom not to do this. If he'll specif= y > same masks in them, he'll get no addresses out of the syscall.) This error case is (one of) the problems I propose avoiding. You also need much more text to describe the requred/excluded flags interactions and edge cases than saying that a flag must have a value equal to corresponding bit in ~negated_flags to be matched by requried/anyof masks. > > IOW my proposal is to replace branches in the masks interpretation (if > > in one set then matches but if in another set then doesn't; if flags > > match ... ) with plain calculation (flag is matching when equals > > ~negated_flags; if flags match the masks ...). Best Regards Micha=C5=82 Miros=C5=82aw