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 09838C433EF for ; Mon, 25 Jul 2022 13:51:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 87F44900002; Mon, 25 Jul 2022 09:51:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 82F5A8E0001; Mon, 25 Jul 2022 09:51:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 71F57900002; Mon, 25 Jul 2022 09:51:30 -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 642058E0001 for ; Mon, 25 Jul 2022 09:51:30 -0400 (EDT) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 38E74C11A8 for ; Mon, 25 Jul 2022 13:51:30 +0000 (UTC) X-FDA: 79725759540.03.8072774 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by imf06.hostedemail.com (Postfix) with ESMTP id 75F3B18008F for ; Mon, 25 Jul 2022 13:51:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1658757089; x=1690293089; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:in-reply-to; bh=oTuDloTSJTh/mR+M/XiSHbTOyhEzShF3fA4W384Cvww=; b=Ds2pSLlWVIidDbEe9Xc9ZYqVrdbnK68WOZl7DX2D7CQlLCaDWO2W0Up/ btEtc8A4bf8nqknKYDO2ocpxzueK7Tb89nT4I7m2nCps495GAU9YhFtHS AP9EyVv1lWGor4qdhbBTGiIKdSOqY4bMOyGH7C19RFH2+eS3awr13/RLE 94giyYNuAh77EqIBwKme6Hr/uLahikXQfJUfGAuPNq1INlcNmiZgoYxqG z3YFBjnxrEfcBcEbKSkc+oa3szRNeIHiAadnPeTs4ArMaGmle7JgtmSLh oRguUyBelWCcxA/RWDOv53VbICQ5HctswfwUfsOCkkoVckW0+kY0DXKDI w==; X-IronPort-AV: E=McAfee;i="6400,9594,10418"; a="288886684" X-IronPort-AV: E=Sophos;i="5.93,193,1654585200"; d="scan'208";a="288886684" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Jul 2022 06:51:28 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.93,193,1654585200"; d="scan'208";a="627458071" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.193.75]) by orsmga008.jf.intel.com with ESMTP; 25 Jul 2022 06:51:16 -0700 Date: Mon, 25 Jul 2022 21:46:28 +0800 From: Chao Peng To: Sean Christopherson 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 , 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: <20220725134628.GC304216@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> <39067d09-b32b-23a6-ae0e-00ac2fe0466c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658757089; a=rsa-sha256; cv=none; b=ULsXJUxTT2WfCYPMnF6MAVMfTP8cTBCh1mxJfhxZbukJs+sTz+WL9/sS0f+QmbpeqJuoaT oOcTX2yAe+uki6H26lvnI9YG6oqzFHRXEnlEHmyAkcJxRNVkCT6YPUDX0Ka0pNj8RFINt8 8vbsC8jrjDvMfCZHMBwpi0JpFHRwncg= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=Ds2pSLlW; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf06.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 134.134.136.65) smtp.mailfrom=chao.p.peng@linux.intel.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658757089; 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=n4oMSroqC6jZx25iZAe+AdjGV0RDiU18++7bb4XGq4Q=; b=L39YFgOAZ/VN603CfAguQ1+hllaTYX0W63JCnyuelCDerS54v+Q90xoL4Nq4bUrRYvMjH7 DM8HjoM5webhAD10fEGrkxElNOqxjuLB0cGXsGCigtp1Pxek9fLUDNFLXQhvBl1RTui4/4 JzflT90m6+lDnqsvwnYl4gyfEFLTLVE= X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 75F3B18008F Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=Ds2pSLlW; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf06.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 134.134.136.65) smtp.mailfrom=chao.p.peng@linux.intel.com X-Stat-Signature: muu5xspwpwqg1jfm1yf881gedhy9rg4m X-HE-Tag: 1658757089-893149 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 03:05:09PM +0000, Sean Christopherson wrote: > On Thu, Jul 21, 2022, David Hildenbrand wrote: > > On 21.07.22 11:44, David Hildenbrand wrote: > > > On 06.07.22 10:20, Chao Peng 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. > > > > Correction: on read() we don't allocate a fresh page. But on read faults > > we would. So this comment here needs clarification. > > Not just the comment, the code too. The intent of F_SEAL_AUTO_ALLOCATE is very > much to block _all_ implicit allocations (or maybe just fault-based allocations > if "implicit" is too broad of a description). So maybe still your initial suggestion F_SEAL_FAULT_ALLOCATIONS? One reason I don't like it is the write() ioctl also cause allocation and we want to prevent it. Chao