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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4FBFC6379F for ; Wed, 22 Feb 2023 10:11:42 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EEDCB6B0071; Wed, 22 Feb 2023 05:11:41 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E9DD86B0073; Wed, 22 Feb 2023 05:11:41 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D8C846B0074; Wed, 22 Feb 2023 05:11:41 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id CA9726B0071 for ; Wed, 22 Feb 2023 05:11:41 -0500 (EST) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 9195C1A09FD for ; Wed, 22 Feb 2023 10:11:41 +0000 (UTC) X-FDA: 80494511202.24.6F68F15 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by imf18.hostedemail.com (Postfix) with ESMTP id 9BEB81C0019 for ; Wed, 22 Feb 2023 10:11:38 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=THO6C2nl; spf=pass (imf18.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com; dmarc=pass (policy=reject) header.from=collabora.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1677060699; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=QfYbnIJVMnR8NDXSAC1rHjqQlzXJL9w9+ZZI4VSPtKQ=; b=GQR9fKePaGp53v3SNYQJT+VaPNuOHA7KIv2F/NMgC+RNyaLt7ABmFnwW+SzDXtiko9tqUi 4KDh3UjtU3iGTXgvEB6ByKLsXz5iglygpVqaC8Lx6p/5CWgLYSAK9xFjxGxbiTlNra41at GkDbs02MwBZYYZg28MVweKQND4oN//4= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=THO6C2nl; spf=pass (imf18.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com; dmarc=pass (policy=reject) header.from=collabora.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1677060699; a=rsa-sha256; cv=none; b=RrJ0rEXGTM9P2AauGl8BtmQP9j1cMllbhGsFTORU6/NuBZaxfJl31NHs3Mfk6qCA/+ZN3q NVWPNAMgTki3aloZa3hI+zfCIrQhppsw51DZQzfG47WXOK1g4woSHWvCvp65/KX9imwZ7H 7pUlVcrbdT1K9wbKKh2Gk/chYZ7A4rc= Received: from [192.168.10.12] (unknown [39.45.217.110]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id A5DDC660215E; Wed, 22 Feb 2023 10:11:13 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1677060696; bh=NXcADlIg87ZcIH/rmsyo4aL3MQ7pMgv/uza3wicJzPE=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=THO6C2nljd7jwF7SJMnlnE7I332qeIT0Y2k8E29LrPGIExRXzjvMgw2wW1j8gtrfj 7HIfAe/s+pErJgN8cPqOVUFTraUY0QBLiW7zuNwVh2QSz2yv7BI1HRD+MVET5GEVvO Pba592XrXyPsLQHCWUkk9rL1Yxodfefnz9GqUDJdle0ki/yLi2TxYibwN5M3e1gdtZ k0vOAPGfooR81D9X2QnPI1IMAAYSMNkDI9vH0iyVrxnIiuqQZj5sUtAjLUbMB2IgPK szoZfOQEwiY4wu8Loq7NoTH+jIoW8Rq4kmmH+GrhvSjYbbDo7d2Gb3r7OX+BlQxBWv NxJtjfUNiZ0Ow== Message-ID: <6d2b40c6-bed9-69a6-e198-537b50953acd@collabora.com> Date: Wed, 22 Feb 2023 15:11:06 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Cc: Muhammad Usama Anjum , 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 Subject: Re: [PATCH v10 3/6] fs/proc/task_mmu: Implement IOCTL to get and/or the clear info about PTEs To: =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= References: <20230202112915.867409-1-usama.anjum@collabora.com> <20230202112915.867409-4-usama.anjum@collabora.com> <36ddfd75-5c58-197b-16c9-9f819099ea6d@collabora.com> Content-Language: en-US From: Muhammad Usama Anjum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9BEB81C0019 X-Stat-Signature: hiknqd746rsjqf9g7giao39hguneuxry X-Rspam-User: X-HE-Tag: 1677060698-684532 X-HE-Meta: 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 X26Z6aK5 dZ9BPiZnejxs+pjIAeFqMBzjyy2Ki7JBa05/gSsGwUZnfT4oimIkBX/cbKfnzntM5h1LHuEpQuGri5RPj829nAa7qjsVA4Ta9+qk7zb2tCk9DKBqBqjVQPOFVtVzEvA2gdGMx/e6hnMPFcy6T+T1eNx2pAGbq1AuNCrCgehI7lvGX5lPZ+MirB2hRnU4fVfKiDSTGVBeKjef+thINjg6dEuwW9c2AUJGokldDpz1V/uRYVOSYlcKQHJjRa+JRrCAyOjDLuxSlidKLCUsN8SCOrS6FavN/DHqeh+PRfPM77S+KRhNroICdt8YYCImSH4QLQ8LFmYOLWxUxU2IbtCLSLoVfphKXjPZenOLCPHLb5yWY0MiReT8DKJlaNQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2/21/23 5:42 PM, Michał Mirosław wrote: > On Tue, 21 Feb 2023 at 11:28, Muhammad Usama Anjum > wrote: >> >> Hi Michał, >> >> Thank you so much for comment! >> >> On 2/17/23 8:18 PM, Michał Mirosław 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 selected. >> 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 applying >>> the page selection using following masks; >> Sorry I'm unable to understand the negation (which is XOR?). Lets look 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 which has >> changed the page flag. It isn't making sense to me. Why the page flag bit >> is being fliped? >> >> When Anrdei had proposed these masks, they seemed like a fancy way of >> filtering inside kernel and it was straight forward to understand. These >> 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. For a page to get selected, the page flags must fulfill the criterion of all the specified masks. If a flag is present in both required_mask and excluded_mask, the required_mask would select a page. But exculded_mask would drop the page. So page page would be dropped. It is responsibility of the user to correctly specify the flags. matched = true; if (p->required_mask) matched = ((p->required_mask & bitmap) == p->required_mask); if (matched && p->anyof_mask) matched = (p->anyof_mask & bitmap); if (matched && p->excluded_mask) matched = !(p->excluded_mask & bitmap); if (matched && bitmap) { // page selected } Do you accept/like this behavior of masks after explaintation? > (Note: the XOR is applied only to the value of the flags for the > purpose of testing page-selection criteria.) > > So: > 1. if a flag is not set in negated_flags, but set in required_flags, > then it means "this flag must be one" - equivalent to it being set in > required_flag (in your current version of the API). > 2. if a flag is set in negated_flags and also in required_flags, then > it means "this flag must be zero" - equivalent to it being set in > excluded_flags. Lets translate words into table: pageflags required_flags negated_flags matched 1 1 0 yes 0 1 1 yes > > The same thing goes for anyof_flags: if a flag is set in anyof_flags, > then for it to be considered matched: > 1. it must have a value of 1 if it is not set in negated_flags > 2. it must have a value of 0 if it is set in negated_flags pageflags anyof_flags negated_flags matched 1 1 0 yes 0 1 1 yes > > 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. > The example > code has a bug though, in that if anyof_flags is zero it will never > match. Let me fix the selection part: > > // calc. a mask of flags that have expected ("active") values > tested_flags = page_flags ^ negated_flags; > // are all required flags in "active" state? [== all zero when negated] > if (~tested_flags & required_mask) > skip page; > // is any extra flag "active"? > if (anyof_flags && !(tested_flags & anyof_flags)) > skip page; > After taking a while to understand this and compare with already present flag system, `negated flags` is comparatively difficult to understand while already present flags seem easier. > > Best Regards > Michał Mirosław -- BR, Muhammad Usama Anjum