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 X-Spam-Level: X-Spam-Status: No, score=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F24E8C433DB for ; Tue, 16 Mar 2021 19:19:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6C997650D9 for ; Tue, 16 Mar 2021 19:19:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6C997650D9 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B31806B0036; Tue, 16 Mar 2021 15:19:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AE2646B006C; Tue, 16 Mar 2021 15:19:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 959496B006E; Tue, 16 Mar 2021 15:19:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0234.hostedemail.com [216.40.44.234]) by kanga.kvack.org (Postfix) with ESMTP id 779756B0036 for ; Tue, 16 Mar 2021 15:19:34 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 2A1CC2C37 for ; Tue, 16 Mar 2021 19:19:34 +0000 (UTC) X-FDA: 77926701468.21.DD62817 Received: from mail-ed1-f54.google.com (mail-ed1-f54.google.com [209.85.208.54]) by imf23.hostedemail.com (Postfix) with ESMTP id A7449A0000FA for ; Tue, 16 Mar 2021 19:19:33 +0000 (UTC) Received: by mail-ed1-f54.google.com with SMTP id h10so22870056edt.13 for ; Tue, 16 Mar 2021 12:19:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=h6Vzk8VT7CSO7U742Td38RGtE0keze+h9TLzW6HQXXc=; b=GydREVbKMbv810VnAeG22Q4t4zqHtGsMA9e8miBDPJGGE9w0F9kExYqC06TyXXRPc7 iEddchnK6lflk84Nu7mNvXulzjvPFLncGpGAUdnYyV/bNlTZQZiArosRQmNyVGvQF63g gbtomYgz3qPyaX36A2QZ9ug2Pp6FhwhmyKPD3mweUqrbjdBRMmGogPr/Hi2CmT/lkc2b uP+3zZ1auReC4wDx/38GAeC2FGkCg4u1uryGVuzUmFMjVeWlB3VzI5eOwnntuzHiH45C rNYx+/zNWfTkNd70LDaDJLOXfRMtlBOQSGfUrty0sXa6KW/gP1CirEWRF1kz+DAiFaek dE2w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=h6Vzk8VT7CSO7U742Td38RGtE0keze+h9TLzW6HQXXc=; b=LVkb0DzKMql9E47k8qT3bKMp/rtDRh6Nk2zIE+9QYqRaZuIy5RuYs49+37nEuoQMgW vCQdwOJH29TAkEpnOKmp3HeIKUO/bTWrzlgnwqSNfvCXzrRvpgy6eFeEQhdaypPAjQ+m ydPHjexmf1neoAIKTJ34xt6zH+DogHcjZ7ssC7hTAglJ2rO1119WwAopWv0LVtv7XiiU r3ygGuXutuCw28Cw5mnfSA6GvM02LQbtckWZR31LOgPRCoXmjTmkFpvLnwW9BXTWymcL Y0Sc6s4BKU5UorumL2G3eTCp2LM4hLJh75J5yrzBJjFY+XlcqnRYqerBETVZxdbTKwD/ v65Q== X-Gm-Message-State: AOAM5319L4p0uwA3AcnHrR6QABIKNT5CVsuD3c73yWBSg8y2Qn1BuuCm szC0lfnTc0Eps8ADm1W7L7BBtBtX+Ftz/Lx7XCcv7w== X-Google-Smtp-Source: ABdhPJzhGyum+xNFOIbL81WhK9++sMcatEGBHuDj59K3Cg00UwnFJJqkJvO+tbIT+09NtrXSAHWt2g64ElP4JLrxVQ8= X-Received: by 2002:a05:6402:304b:: with SMTP id bu11mr36682115edb.157.1615922372300; Tue, 16 Mar 2021 12:19:32 -0700 (PDT) MIME-Version: 1.0 References: <20210303175235.3308220-1-bgeffon@google.com> In-Reply-To: From: Brian Geffon Date: Tue, 16 Mar 2021 15:18:55 -0400 Message-ID: Subject: Re: [PATCH] mm: Allow shmem mappings with MREMAP_DONTUNMAP To: Hugh Dickins Cc: Andrew Morton , Axel Rasmussen , Lokesh Gidra , Mike Rapoport , Peter Xu , "Michael S . Tsirkin" , LKML , linux-mm , Andy Lutomirski , Vlastimil Babka , Andrea Arcangeli , Sonny Rao , Minchan Kim , "Kirill A . Shutemov" , Dmitry Safonov , Michael Kerrisk , Alejandro Colomar Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: 6dgdajs7eo4d3gq7b54gbx9g64sgga6q X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: A7449A0000FA Received-SPF: none (google.com>: No applicable sender policy available) receiver=imf23; identity=mailfrom; envelope-from=""; helo=mail-ed1-f54.google.com; client-ip=209.85.208.54 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615922373-603288 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: Hi Hugh, Thanks for this suggestion, responses in line. > A better patch would say: > > - if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) || > - vma->vm_flags & VM_SHARED)) > + if ((flags & MREMAP_DONTUNMAP) && > + (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))) > return ERR_PTR(-EINVAL); > > VM_DONTEXPAND is what has long been used on special mappings, to prevent > surprises from mremap changing the size of the mapping: MREMAP_DONTUNMAP > introduced a different way of expanding the mapping, so VM_DONTEXPAND > still seems a reasonable name (I've thrown in VM_PFNMAP there because > it's in the VM_DONTEXPAND test lower down: for safety I guess, and best > if both behave the same - though one says -EINVAL and the other -EFAULT). I like this idea and am happy to mail a new patch. I think it may make sense to bring the lower block up here so that it becomes more clear that it's not duplicate code and that the MREMAP_DONTUNMAP case returns -EINVAL and other cases return -EFAULT. I wonder if the -EFAULT error code would have made more sense from the start for both cases, do you have any thoughts on changing the error code at this point? > With that VM_DONTEXPAND check in, Dmitry's commit cd544fd1dc92 > ("mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio") > can still be reverted (as you agreed on 28th December), even though > vma_is_anonymous() will no longer protect it. I agree and if Dmitry does not have time I would be happy to mail a revert to cd544fd1dc92 as we discussed in [1]. Dmitry, would you like me to do that? > Was there an mremap(2) man page update for MREMAP_DONTUNMAP? > Whether or not there was before, it ought to get one now. Yes, the mremap(2) man page was updated when this flag was added and it will require a further update to reflect this expanded mapping support. Thanks Brian 1. https://lkml.org/lkml/2020/12/28/2340