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 09643C54EE9 for ; Thu, 22 Sep 2022 19:49:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2DDC26B0071; Thu, 22 Sep 2022 15:49:24 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2669A6B0072; Thu, 22 Sep 2022 15:49:24 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 10874940007; Thu, 22 Sep 2022 15:49:24 -0400 (EDT) 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 02E0A6B0071 for ; Thu, 22 Sep 2022 15:49:24 -0400 (EDT) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id A755F805D5 for ; Thu, 22 Sep 2022 19:49:23 +0000 (UTC) X-FDA: 79940760606.23.03C9DFF Received: from mail-pl1-f177.google.com (mail-pl1-f177.google.com [209.85.214.177]) by imf29.hostedemail.com (Postfix) with ESMTP id 5BD81120011 for ; Thu, 22 Sep 2022 19:49:23 +0000 (UTC) Received: by mail-pl1-f177.google.com with SMTP id d11so2373895pll.8 for ; Thu, 22 Sep 2022 12:49:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date; bh=AOIMXA4PI9BYXrk6/Ja2mOKlrFIROrj5K/ieUQQwXS4=; b=h1quGJbzNcYbvksztMmJbAj4021+BcmdngI9oVLKqryAXjZOZrGY+bZOFcLzMWlozZ LAcA23Adi1Jic4pRnJCptlWTG4EcoRJkXHfvedp0K1HaJOCXyEXxuhzgdof/jPIDOZEe ebqjyLF5ANcpzYiinKi6eaQnqth3W4n2V8+InjN4EWNaK7npJ/bYc7FhRS+iyNb4HHPb Efk7QXZ7wTcSNyFHTH7NWGDPMQ4YLD125sVU1j3HVB2TkIAvgthLngw1wMrAfORH5ZfR U8+tmRxUsuSWAVFhBHQcUHbhvue7DyoPTDpJKMkc7xktoeaZV8RiJlYUMocHTDHlXZyf XJ3w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date; bh=AOIMXA4PI9BYXrk6/Ja2mOKlrFIROrj5K/ieUQQwXS4=; b=MkpTrkTtazsL5PJuUCjZBNFCs3NLTDfHMsf+GfXgac4O7WoKzXJ4bRHw7Q+zjtksbh Cm2FJkilGQnXEJVQWcTV1+WrbeN+WCBkTRQTHQ2eXm5wFJEXDqxuDlwwttRS57Sz8b6a H71M2AflXoA000FgqLq2cKKEBWqYzuxilVaayFFEUHpvKauplJ7DWgIa9R6KgQB8tFDd yQAzPrwslrz8eSi0/YoTLM8VLIyPVI5c/O1mMp1p/7ULStamoQ6y4ZzVpwhn2pbKJ2si CwZEBaRVzXcw+TYNIcHcqMTBcRwEgdiyaZsWM8TURdN7WHhWDKHSYEMetOr9FaFVQ8d5 1Lvw== X-Gm-Message-State: ACrzQf0X9U4bvU3WgWDod2/tONiJDlRmPyCUL9x2gnFdMh8lJym09+mC aAb/SdBAmmlpfFvJPXZnrNxhjg== X-Google-Smtp-Source: AMsMyM7xkIpUg/GEtYg3CdJDso/M2NS+vljJqn+Iz/Og0ecRlPYRkH7bufKUsfNRGuIjAMJq7OVhXg== X-Received: by 2002:a17:90a:644e:b0:200:422c:6b1 with SMTP id y14-20020a17090a644e00b00200422c06b1mr5394594pjm.183.1663876162098; Thu, 22 Sep 2022 12:49:22 -0700 (PDT) Received: from google.com (7.104.168.34.bc.googleusercontent.com. [34.168.104.7]) by smtp.gmail.com with ESMTPSA id a10-20020a170902ecca00b00172897952a0sm4576315plh.283.2022.09.22.12.49.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Sep 2022 12:49:21 -0700 (PDT) Date: Thu, 22 Sep 2022 19:49:18 +0000 From: Sean Christopherson To: "Wang, Wei W" Cc: Chao Peng , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-api@vger.kernel.org" , "linux-doc@vger.kernel.org" , "qemu-devel@nongnu.org" , Paolo Bonzini , Jonathan Corbet , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "x86@kernel.org" , "H . Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A . Shutemov" , "Lutomirski, Andy" , "Nakajima, Jun" , "Hansen, Dave" , "ak@linux.intel.com" , "david@redhat.com" , "aarcange@redhat.com" , "ddutile@redhat.com" , "dhildenb@redhat.com" , Quentin Perret , Michael Roth , "Hocko, Michal" , Muchun Song Subject: Re: [PATCH v8 1/8] mm/memfd: Introduce userspace inaccessible memfd Message-ID: References: <20220915142913.2213336-1-chao.p.peng@linux.intel.com> <20220915142913.2213336-2-chao.p.peng@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663876163; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=AOIMXA4PI9BYXrk6/Ja2mOKlrFIROrj5K/ieUQQwXS4=; b=UEjOHTjdaHw3VbVLs+M6HPdC7zgFPwcNDho2PV48KE7+E8MiGzmmLilW7fRoccKV8yYcxC T9S9IFgWcdtGv1ZVVZXqvDpF0ZUWCcZck1zfdyO3cYs9j2GQ27w/YFkmb9h2o48aLfX7+V whSJvqYT+2VUM5+XYYg7j98YpR6RTc0= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=h1quGJbz; spf=pass (imf29.hostedemail.com: domain of seanjc@google.com designates 209.85.214.177 as permitted sender) smtp.mailfrom=seanjc@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663876163; a=rsa-sha256; cv=none; b=i/dTmLLIF6cshqUOZETpVGV/rKdPDsKY2oDIrmD4nAMJOa7k2FaO4cHPlnr4F87nKNEcaT pqhEylJKAvMujFCKuw5jbVqp8dW0Y/vqdpGmwgDlWTGGXgilc4aTfhAWbbbIyYzb5ujqHJ QW+QgKfQ7cIe7cRyqtFI4EkJbQzw0tU= X-Stat-Signature: y3ci16w9of4ujdsq6w8xhsf9u8rsgwqy X-Rspamd-Queue-Id: 5BD81120011 X-Rspam-User: Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=h1quGJbz; spf=pass (imf29.hostedemail.com: domain of seanjc@google.com designates 209.85.214.177 as permitted sender) smtp.mailfrom=seanjc@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam03 X-HE-Tag: 1663876163-672365 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 Thu, Sep 22, 2022, Wang, Wei W wrote: > On Thursday, September 15, 2022 10:29 PM, Chao Peng wrote: > > +int inaccessible_get_pfn(struct file *file, pgoff_t offset, pfn_t *pfn, > > + int *order) > > Better to remove "order" from this interface? Hard 'no'. > Some callers only need to get pfn, and no need to bother with > defining and inputting something unused. For callers who need the "order", > can easily get it via thp_order(pfn_to_page(pfn)) on their own. That requires (a) assuming the pfn is backed by struct page, and (b) assuming the struct page is a transparent huge page. That might be true for the current implementation, but it most certainly will not always be true. KVM originally did things like this, where there was dedicated code for THP vs. HugeTLB, and it was a mess. The goal here is very much to avoid repeating those mistakes. Have the backing store _tell_ KVM how big the mapping is, don't force KVM to rediscover the info on its own.