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 181F9CCA48B for ; Mon, 25 Jul 2022 13:59:19 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6D4456B0071; Mon, 25 Jul 2022 09:59:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 684466B0072; Mon, 25 Jul 2022 09:59:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 525848E0001; Mon, 25 Jul 2022 09:59:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 44B496B0071 for ; Mon, 25 Jul 2022 09:59:19 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 21BF6C01E4 for ; Mon, 25 Jul 2022 13:59:19 +0000 (UTC) X-FDA: 79725779238.26.561C7FC Received: from mga06.intel.com (mga06b.intel.com [134.134.136.31]) by imf16.hostedemail.com (Postfix) with ESMTP id 4E28F1800C0 for ; Mon, 25 Jul 2022 13:59:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1658757558; x=1690293558; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:in-reply-to; bh=SebOtSYgmnmuVPxznPkmfUK1/G0u2P5tlySsXcB/PUU=; b=GTCKUWo8tUu7OnR0tqR/RJCVcjNpubpotk7J1TEn1IQjygv5xsuPebHb BL8zoHVm4YlDF8l3KA7qjzRIPPps4z924TFLiuNRFeTmBBSy4TCeza5N9 5BQdawnZj9DfGkAjIpDMQiKx+p+4/YRS+sWjDJMcXHiput6Nh++syNsk/ qyltJ4arBDgFE+xB/xAwoG61aN4aDHKorCWAJpqualb0ao51AF9KlGAlD wizPm3nbokq0vTKW5misbyAr2Wfd0o4zKTDORAc2XkGxtCLxplAkmY3F0 7UOYxNoZI8gb9AMEpQJme9td558i21N39a+PDvOQFr1SWPUAgQummg6PX Q==; X-IronPort-AV: E=McAfee;i="6400,9594,10418"; a="349401680" X-IronPort-AV: E=Sophos;i="5.93,193,1654585200"; d="scan'208";a="349401680" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Jul 2022 06:59:16 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.93,193,1654585200"; d="scan'208";a="627460234" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.193.75]) by orsmga008.jf.intel.com with ESMTP; 25 Jul 2022 06:59:04 -0700 Date: Mon, 25 Jul 2022 21:54:16 +0800 From: Chao Peng To: "Gupta, Pankaj" Cc: David Hildenbrand , 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, linux-kselftest@vger.kernel.org, Paolo Bonzini , Jonathan Corbet , Sean Christopherson , 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" , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com, Muchun Song Subject: Re: [PATCH v7 01/14] mm: Add F_SEAL_AUTO_ALLOCATE seal to memfd Message-ID: <20220725135416.GD304216@chaop.bj.intel.com> Reply-To: Chao Peng References: <20220706082016.2603916-1-chao.p.peng@linux.intel.com> <20220706082016.2603916-2-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=1658757558; h=from:from:sender:reply-to: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=1nHQLyVJ3/1Ms7n7x5SErZ0pVhvBpRBhB4IAYhMaAbk=; b=wrgmE91gRQKb9mvamx5lSCySDzvwifcqntfeNBCGvkMt4F/xV7BHlC3sNRY14j3NKIeW96 pF07oJVRgshY2/3FG6sbiHk5g3JgHhilvGguKj9NLX93rKsnHaHmaoH8lKcpzFEJcUYgfn BhellFsEkdrOwRBDmf4JiqJxyGOnxA8= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=GTCKUWo8; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf16.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 134.134.136.31) smtp.mailfrom=chao.p.peng@linux.intel.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658757558; a=rsa-sha256; cv=none; b=0V1bF6wxcU3ghhIJHC3aYZmwM7Ffp0TCU1oeOhzLBTMuaaKytTw7to3HM28G5DzF7GzAhr HTY93pureOQOH4yXhh0pEXVr1snG+3bLmgGANito/nu9yF63i1FeUcabxVN4ruKmxWYFde f9wZ9DFfyoN4P7K7J50BdhGtiPTvoGw= X-Stat-Signature: 4mkiethd78ga8qhbqqnk8kix5poh5qy6 X-Rspamd-Queue-Id: 4E28F1800C0 X-Rspam-User: X-Rspamd-Server: rspam12 Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=GTCKUWo8; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf16.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 134.134.136.31) smtp.mailfrom=chao.p.peng@linux.intel.com X-HE-Tag: 1658757558-645815 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, Jul 21, 2022 at 12:27:03PM +0200, Gupta, Pankaj wrote: > > > > Normally, a write to unallocated space of a file or the hole of a sparse > > > file automatically causes space allocation, for memfd, this equals to > > > memory allocation. This new seal prevents such automatically allocating, > > > either this is from a direct write() or a write on the previously > > > mmap-ed area. The seal does not prevent fallocate() so an explicit > > > fallocate() can still cause allocating and can be used to reserve > > > memory. > > > > > > This is used to prevent unintentional allocation from userspace on a > > > stray or careless write and any intentional allocation should use an > > > explicit fallocate(). One of the main usecases is to avoid memory double > > > allocation for confidential computing usage where we use two memfds to > > > back guest memory and at a single point only one memfd is alive and we > > > want to prevent memory allocation for the other memfd which may have > > > been mmap-ed previously. More discussion can be found at: > > > > > > https://lkml.org/lkml/2022/6/14/1255 > > > > > > Suggested-by: Sean Christopherson > > > Signed-off-by: Chao Peng > > > --- > > > include/uapi/linux/fcntl.h | 1 + > > > mm/memfd.c | 3 ++- > > > mm/shmem.c | 16 ++++++++++++++-- > > > 3 files changed, 17 insertions(+), 3 deletions(-) > > > > > > diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h > > > index 2f86b2ad6d7e..98bdabc8e309 100644 > > > --- a/include/uapi/linux/fcntl.h > > > +++ b/include/uapi/linux/fcntl.h > > > @@ -43,6 +43,7 @@ > > > #define F_SEAL_GROW 0x0004 /* prevent file from growing */ > > > #define F_SEAL_WRITE 0x0008 /* prevent writes */ > > > #define F_SEAL_FUTURE_WRITE 0x0010 /* prevent future writes while mapped */ > > > +#define F_SEAL_AUTO_ALLOCATE 0x0020 /* prevent allocation for writes */ > > > > Why only "on writes" and not "on reads". IIRC, shmem doesn't support the > > shared zeropage, so you'll simply allocate a new page via read() or on > > read faults. > > > > > > Also, I *think* you can place pages via userfaultfd into shmem. Not sure > > if that would count "auto alloc", but it would certainly bypass fallocate(). > > I was also thinking this at the same time, but for different reason: > > "Want to populate private preboot memory with firmware payload", so was > thinking userfaulftd could be an option as direct writes are restricted? If that can be a side effect, I definitely glad to see it, though I'm still not clear how userfaultfd can be particularly helpful for that. Chao > > Thanks, > Pankaj > > > >