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 19145C43334 for ; Fri, 10 Jun 2022 00:11:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6637F8D0068; Thu, 9 Jun 2022 20:11:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 611CA8D0064; Thu, 9 Jun 2022 20:11:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4B2588D0068; Thu, 9 Jun 2022 20:11:35 -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 3B4F48D0064 for ; Thu, 9 Jun 2022 20:11:35 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id E335D35A25 for ; Fri, 10 Jun 2022 00:11:34 +0000 (UTC) X-FDA: 79560397308.18.47A70C1 Received: from mail-oa1-f54.google.com (mail-oa1-f54.google.com [209.85.160.54]) by imf11.hostedemail.com (Postfix) with ESMTP id 6AA1D40066 for ; Fri, 10 Jun 2022 00:11:34 +0000 (UTC) Received: by mail-oa1-f54.google.com with SMTP id 586e51a60fabf-f2cbceefb8so1381371fac.11 for ; Thu, 09 Jun 2022 17:11:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=lN+fOqwv9bBcDqIpukqHItG5mOqsK9h2lCdbXTf1cPM=; b=DayT0SdBt1ymTKyry+8RI8dWvFXfKXAgjmO8VhNnB1yoDZK63YuzcCUTHD3X1Z3+t5 KxmGEbccYszaa9LA1rH+uPvXkUot/k7y+eYJ5dVw1vcNDUZMV9ll/y/F+7N08dr0Wzcn baBzETzPA15Z2tn9QgoF5S7+WOA0j8RJa/fH3l+HKIsIdEIRN75ENG6RuJQTaJE4f7s+ tdQ6ePOMDHk+W48X2uZ7KmmqPYEcwu7pMK65fJXjpYRLWoV5X97j/IkcgrkGUpYpxwIB E5LIO66muSm/XASIShQU2K4+YUS/ejVNHYtSotPk8eFHXkkvvETkJhzMm8POKoBM9Wup sSZg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=lN+fOqwv9bBcDqIpukqHItG5mOqsK9h2lCdbXTf1cPM=; b=dB++3mYSNBF/AWk90EJ0v4gLqPl42tApMYL7Aov0idhzplfdE/AVKV8DFTCNNpwr37 H0PrFLbQ/m4XCssWFthXobb5FziCG6RTSEkWetXYWfOjbkmbV1Q34UUzQn88mzas24Ac xeDnQ0qmpzcqHKZ1UEQTPesk58YIni1nJr3RwOo9+Wegc/6CSYElPL3l5CnUsi1u7/x1 fA9S/IFNTWDUYMxRICF0VmU24dozOib/yMR80MP+3bF19bs9Pn9ZLikkhy1EcJBkKEqN Bea/JCAtyCLI+KxGt0FZNK6K0VONEEu0l40tSOqhAQMFRGtzAtR18MJJCxLP4T5PkixZ IKfg== X-Gm-Message-State: AOAM533xKHG0zxjFWOzeXY/S6DjCmsVX6nAxxS4ubH4iR490tdY+vBwj cMoxM+k12E3YTrfXryLptTKmHmGR1yp3tQEBU3mgAw== X-Google-Smtp-Source: ABdhPJzdaT0C30mX9Im9rqGsL6x1Rmi0294lLn68XE92+pqgxWwSN0AqB6f3CMYnEGDUJ7ZH1btvuZX8xfTHzXelZbU= X-Received: by 2002:a05:6870:b616:b0:e2:f8bb:5eb with SMTP id cm22-20020a056870b61600b000e2f8bb05ebmr3338490oab.218.1654819893261; Thu, 09 Jun 2022 17:11:33 -0700 (PDT) MIME-Version: 1.0 References: <20220519153713.819591-1-chao.p.peng@linux.intel.com> <20220607065749.GA1513445@chaop.bj.intel.com> <20220608021820.GA1548172@chaop.bj.intel.com> In-Reply-To: <20220608021820.GA1548172@chaop.bj.intel.com> From: Marc Orr Date: Thu, 9 Jun 2022 17:11:21 -0700 Message-ID: Subject: Re: [PATCH v6 0/8] KVM: mm: fd-based approach for supporting KVM guest private memory To: Chao Peng Cc: Vishal Annapurve , kvm list , LKML , 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 , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86 , "H . Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Yu Zhang , "Kirill A . Shutemov" , Andy Lutomirski , Jun Nakajima , Dave Hansen , Andi Kleen , David Hildenbrand , aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com Content-Type: text/plain; charset="UTF-8" ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1654819894; a=rsa-sha256; cv=none; b=HtCH+fMdVOV7LZuJmm6YXn1DJEUClNnnlB5Ndha8aVFH6nJTzyt4jjeOTKop0tG1bsYox1 6qJH7UxSQKMnL8DK08uwgdotKa1BLaRo1aV2DyqHcydBYU5vgrj0Ax6FLN/TJ1wZ2GlsJp mnchNcwULDoieIlVL2C3PEmgSCCpI6w= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=DayT0SdB; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf11.hostedemail.com: domain of marcorr@google.com designates 209.85.160.54 as permitted sender) smtp.mailfrom=marcorr@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1654819894; 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=lN+fOqwv9bBcDqIpukqHItG5mOqsK9h2lCdbXTf1cPM=; b=zbrT8EExqR9hoSyXbiPd6tA/IPIsSozJuKuGh5MWujYrYYiFwmVKEof6W32TEN10JBUAcf JL6IFQhs2aflwl+lZaFJvQj+Tvf85Ulv9rNQxvud0CM/oOpBYTN9ceKHdNA2G2VgzdPyFc wSaDo3QyTJ1hSfhtWkILIyNK8BkRpQ8= X-Stat-Signature: rodono7ega11ssgkui6gadqej4i19cke X-Rspam-User: X-Rspamd-Queue-Id: 6AA1D40066 X-Rspamd-Server: rspam07 Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=DayT0SdB; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf11.hostedemail.com: domain of marcorr@google.com designates 209.85.160.54 as permitted sender) smtp.mailfrom=marcorr@google.com X-HE-Tag: 1654819894-472622 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 Tue, Jun 7, 2022 at 7:22 PM Chao Peng wrote: > > On Tue, Jun 07, 2022 at 05:55:46PM -0700, Marc Orr wrote: > > On Tue, Jun 7, 2022 at 12:01 AM Chao Peng wrote: > > > > > > On Mon, Jun 06, 2022 at 01:09:50PM -0700, Vishal Annapurve wrote: > > > > > > > > > > Private memory map/unmap and conversion > > > > > --------------------------------------- > > > > > Userspace's map/unmap operations are done by fallocate() ioctl on the > > > > > backing store fd. > > > > > - map: default fallocate() with mode=0. > > > > > - unmap: fallocate() with FALLOC_FL_PUNCH_HOLE. > > > > > The map/unmap will trigger above memfile_notifier_ops to let KVM map/unmap > > > > > secondary MMU page tables. > > > > > > > > > .... > > > > > QEMU: https://github.com/chao-p/qemu/tree/privmem-v6 > > > > > > > > > > An example QEMU command line for TDX test: > > > > > -object tdx-guest,id=tdx \ > > > > > -object memory-backend-memfd-private,id=ram1,size=2G \ > > > > > -machine q35,kvm-type=tdx,pic=no,kernel_irqchip=split,memory-encryption=tdx,memory-backend=ram1 > > > > > > > > > > > > > There should be more discussion around double allocation scenarios > > > > when using the private fd approach. A malicious guest or buggy > > > > userspace VMM can cause physical memory getting allocated for both > > > > shared (memory accessible from host) and private fds backing the guest > > > > memory. > > > > Userspace VMM will need to unback the shared guest memory while > > > > handling the conversion from shared to private in order to prevent > > > > double allocation even with malicious guests or bugs in userspace VMM. > > > > > > I don't know how malicious guest can cause that. The initial design of > > > this serie is to put the private/shared memory into two different > > > address spaces and gives usersapce VMM the flexibility to convert > > > between the two. It can choose respect the guest conversion request or > > > not. > > > > For example, the guest could maliciously give a device driver a > > private page so that a host-side virtual device will blindly write the > > private page. > > With this patch series, it's actually even not possible for userspace VMM > to allocate private page by a direct write, it's basically unmapped from > there. If it really wants to, it should so something special, by intention, > that's basically the conversion, which we should allow. I think Vishal did a better job to explain this scenario in his last reply than I did. > > > It's possible for a usrspace VMM to cause double allocation if it fails > > > to call the unback operation during the conversion, this may be a bug > > > or not. Double allocation may not be a wrong thing, even in conception. > > > At least TDX allows you to use half shared half private in guest, means > > > both shared/private can be effective. Unbacking the memory is just the > > > current QEMU implementation choice. > > > > Right. But the idea is that this patch series should accommodate all > > of the CVM architectures. Or at least that's what I know was > > envisioned last time we discussed this topic for SNP [*]. > > AFAICS, this series should work for both TDX and SNP, and other CVM > architectures. I don't see where TDX can work but SNP cannot, or I > missed something here? Agreed. I was just responding to the "At least TDX..." bit. Sorry for any confusion. > > > > Regardless, it's important to ensure that the VM respects its memory > > budget. For example, within Google, we run VMs inside of containers. > > So if we double allocate we're going to OOM. This seems acceptable for > > an early version of CVMs. But ultimately, I think we need a more > > robust way to ensure that the VM operates within its memory container. > > Otherwise, the OOM is going to be hard to diagnose and distinguish > > from a real OOM. > > Thanks for bringing this up. But in my mind I still think userspace VMM > can do and it's its responsibility to guarantee that, if that is hard > required. By design, userspace VMM is the decision-maker for page > conversion and has all the necessary information to know which page is > shared/private. It also has the necessary knobs to allocate/free the > physical pages for guest memory. Definitely, we should make userspace > VMM more robust. Vishal and Sean did a better job to articulate the concern in their most recent replies.