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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4077AF31E22 for ; Thu, 9 Apr 2026 15:17:43 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 811EC6B0005; Thu, 9 Apr 2026 11:17:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7E8E16B0089; Thu, 9 Apr 2026 11:17:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7265B6B008A; Thu, 9 Apr 2026 11:17:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 617976B0005 for ; Thu, 9 Apr 2026 11:17:42 -0400 (EDT) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 21D8714047B for ; Thu, 9 Apr 2026 15:17:42 +0000 (UTC) X-FDA: 84639371964.09.38A3963 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf09.hostedemail.com (Postfix) with ESMTP id 67409140014 for ; Thu, 9 Apr 2026 15:17:40 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="Qht0fFe/"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf09.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1775747860; 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=Nbr06xUxYlzqYLI3d13wLA/zrqb+kMb6HGm3++yLxR8=; b=lO2yOPDg9bNSHIpnYnD6i02Lj//itGk0Mcx2Dq1EOtSPUDXlhS9WyAXQ+qBJbOijJjWDey qUW6SSRzwnTqcTV/Ff0oSj+qgBZfi3NEvG1CRzjH8vkPCOZ2gpBsVWcuzkyWToxdR2fyev 3XnJao+Ycj3IyoFAJWeKkUQPtGQRXBc= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1775747860; a=rsa-sha256; cv=none; b=NNDY11tenY7bGI8JtK6TV6xTqmqDIosHheYcl8TTwQTSMHJSRh2Et6Xzs/fDxHbv0Ge5hE Bdx1R/o24eiNrzgMP3tgaW+HK5+K4Z+V/V1qxAupgis3wfgiHuEAkWZiU4KQltRhzcBWro 8BVzBUsQqv44/jkezwi94FYzQkceHPY= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="Qht0fFe/"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf09.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 6697F43FB0; Thu, 9 Apr 2026 15:17:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 926CFC19424; Thu, 9 Apr 2026 15:17:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775747859; bh=sAn4kmA/v5fslLSRk7scPloEbnAS+gMCiSVeAY7naxU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Qht0fFe/mAYbgemHSrTJUo++6CxWDoPmooLnV8Mh+eLdG0nRX6n9/3kNfXrV6fK6u 1IOsS72bzgsHmIjHQsmj6DxoD0K9xK8F+reRJx4L9gaTBzbkYf6VfezuwKZF/KpURX pvpBEUbxTUQPfmb2WFB7KZWcFgNbRMw5kbbjtRbYrhz6xu448ViLBRW7fRq/8sw/5f 99kGM+McX3C63N32vBWaWN2FBEnxBCM61AA3iAzmQbf+YgB6jJLDp3qX9VeDL9aRDR /h1GRhpWpMU+9nwBZlTNSMfqiUxIZ2WCbdPg2XlTs1P/yC7XPqvESzIz3OeKz13Lig CYrrj9wd9kEsw== Date: Thu, 9 Apr 2026 18:17:30 +0300 From: Mike Rapoport To: Pedro Falcato Cc: "Denis M. Karpov" , harry@kernel.org, akpm@linux-foundation.org, Liam.Howlett@oracle.com, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, peterx@redhat.com, brauner@kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, usama.arif@linux.dev Subject: Re: [PATCH v2] userfaultfd: allow registration of ranges below mmap_min_addr Message-ID: References: <20260409103345.15044-1-komlomal@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 67409140014 X-Stat-Signature: p876yyr1em6mfjsfajsup3jgpcis7ead X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1775747860-659269 X-HE-Meta: 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 0rk+PV1X kh8hJlR8ezYyHi1mxn4+rZnxgBbGKTkqTcR0wRlfV2prNdF/SWFoF4AKqGOE5aj1CYKoO5nHsycURM9HCoqip8kgkvMVBn767EjrxeKyfKZG1gqNWH+X1F0kezu90LE1ndwdBRuA56h4ZtVaQbJwh6N+JvMNSbeEb23lV4GYy4TaiKNJkXGjTilf+MS5KNSqxONNIDNURnhbP+VjaBlVXrJYPQgW3mhedjNvvsUw5Ou0O2H7ZqgWU6qfvjvOrUyZc/yEUDyhxmg7JhNPUsmA0/ia0a4BMgYbVEBL1ftOACGJkML67NuI4amNiPonX+J8w1GdJW1Q+eLAOwak= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 09, 2026 at 01:30:07PM +0100, Pedro Falcato wrote: > On Thu, Apr 09, 2026 at 01:33:45PM +0300, Denis M. Karpov wrote: > > The current implementation of validate_range() in fs/userfaultfd.c > > performs a hard check against mmap_min_addr. This is redundant because > > UFFDIO_REGISTER operates on memory ranges that must already be backed > > by a VMA. > > > > Enforcing mmap_min_addr or capability checks again in userfaultfd is > > unnecessary and prevents applications like binary compilers from > > using UFFD for valid memory regions mapped by application. > > > > Remove the redundant check for mmap_min_addr. > > > > Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") > > Signed-off-by: Denis M. Karpov > > Reviewed-by: Pedro Falcato > > This looks relatively safe. However, I'm not sure if we want this in stable. > This has been broken for 11 years now, with no complaints. I believe Denis has a new usecase that wasn't there for those 11 years :) Denis, can you share more details about your usecase for us to better understand importance of backporting this to stable? > -- > Pedro -- Sincerely yours, Mike.