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 ED141C433F5 for ; Mon, 10 Oct 2022 08:29:55 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EF782900002; Mon, 10 Oct 2022 04:29:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E7FD76B0073; Mon, 10 Oct 2022 04:29:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CD2CF900002; Mon, 10 Oct 2022 04:29:54 -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 B29656B0071 for ; Mon, 10 Oct 2022 04:29:54 -0400 (EDT) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 797731C6531 for ; Mon, 10 Oct 2022 08:29:54 +0000 (UTC) X-FDA: 80004366708.25.23AECFD Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by imf13.hostedemail.com (Postfix) with ESMTP id DCD7220022 for ; Mon, 10 Oct 2022 08:29:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1665390592; x=1696926592; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:in-reply-to; bh=5AUxEww8V8qWvvG5bCArmS7RBRQUNOLUMKgyDwR1O0k=; b=mC0prYi4XCb2fnmmDbKr5ZHMRDx9mqzE9wwo9ChA1hExPGhdnHFSz5jJ H3qljG6LEBcGoyP12aVXoN3q6QsrOg0Dze95/twoHjvhdulfwTdeCpkz3 2zfiT1ap23hlrgfritrSHLg/F877ePbjRWn5TcW+MXKFq/PJ1kZ48Rghk sAt+AGhkAlcl1ueHyVkobJo5zHiksMZo427qUZhGXJSzDi1uLiVXr9VLD +eMpYrNA2F0o+alTsCtHDL4VAUEelTgSudZfGU1YcoDd3Z9Gauoi5jqoH LKN6SLpquJbRVVf17YvQv3u6Wr4J9rqEKnmIdQzGz2OGxHfA6j11otA1A A==; X-IronPort-AV: E=McAfee;i="6500,9779,10495"; a="368311404" X-IronPort-AV: E=Sophos;i="5.95,173,1661842800"; d="scan'208";a="368311404" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Oct 2022 01:29:51 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10495"; a="656853060" X-IronPort-AV: E=Sophos;i="5.95,173,1661842800"; d="scan'208";a="656853060" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.193.75]) by orsmga008.jf.intel.com with ESMTP; 10 Oct 2022 01:29:40 -0700 Date: Mon, 10 Oct 2022 16:25:07 +0800 From: Chao Peng To: Jarkko Sakkinen Cc: Sean Christopherson , 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, 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, david@redhat.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com, Muchun Song , wei.w.wang@intel.com Subject: Re: [PATCH v8 2/8] KVM: Extend the memslot to support fd-based private memory Message-ID: <20221010082507.GA3144879@chaop.bj.intel.com> Reply-To: Chao Peng References: <20220915142913.2213336-1-chao.p.peng@linux.intel.com> <20220915142913.2213336-3-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=1665390593; 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=5ILT35YzUwso9MTk7fnZmM+Qn0n6tMqDEE/ok6TvgAw=; b=RO1a5QlDxXgdfoh9X6jSULFC8IfUwxYfcphYUJPeaLpwL/V8Ss7+S9fAwB8jqmN3eT8W6p K64aGpE4Vpg+8fcA44xurASkcezAwIkd5j2Ehtkbmw85oWsdORb6wpuMBWKt3TuxTHw/Ms i11wmWBlWMq2zguaTM2VtGnNNRjLUd4= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=mC0prYi4; spf=none (imf13.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 134.134.136.100) smtp.mailfrom=chao.p.peng@linux.intel.com; dmarc=fail reason="No valid SPF" header.from=intel.com (policy=none) ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1665390593; a=rsa-sha256; cv=none; b=0xvZ1rkiVHG8hqvIw5sTy7tqbpGsBakZ2fCkq69WnevF5CUep6RfqaKAIhCS9tDYdj51nM W4lKeTa2Q5JQc1/9mz3KdHJQRCy8SM2Rab2kDAp9VaNM+1/SEanCvE/uJGwlY22zhNeAPt 8befBmtsviyWGlSga08JugEcxjedBWE= X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: DCD7220022 X-Stat-Signature: 8y9tub9k4out155hpdy5ywbk4auoxmn5 Authentication-Results: imf13.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=mC0prYi4; spf=none (imf13.hostedemail.com: domain of chao.p.peng@linux.intel.com has no SPF policy when checking 134.134.136.100) smtp.mailfrom=chao.p.peng@linux.intel.com; dmarc=fail reason="No valid SPF" header.from=intel.com (policy=none) X-HE-Tag: 1665390592-583002 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 Sat, Oct 08, 2022 at 08:35:47PM +0300, Jarkko Sakkinen wrote: > On Sat, Oct 08, 2022 at 07:15:17PM +0300, Jarkko Sakkinen wrote: > > On Sat, Oct 08, 2022 at 12:54:32AM +0300, Jarkko Sakkinen wrote: > > > On Fri, Oct 07, 2022 at 02:58:54PM +0000, Sean Christopherson wrote: > > > > On Fri, Oct 07, 2022, Jarkko Sakkinen wrote: > > > > > On Thu, Oct 06, 2022 at 03:34:58PM +0000, Sean Christopherson wrote: > > > > > > On Thu, Oct 06, 2022, Jarkko Sakkinen wrote: > > > > > > > On Thu, Oct 06, 2022 at 05:58:03PM +0300, Jarkko Sakkinen wrote: > > > > > > > > On Thu, Sep 15, 2022 at 10:29:07PM +0800, Chao Peng wrote: > > > > > > > > > This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two > > > > > > > > > additional KVM memslot fields private_fd/private_offset to allow > > > > > > > > > userspace to specify that guest private memory provided from the > > > > > > > > > private_fd and guest_phys_addr mapped at the private_offset of the > > > > > > > > > private_fd, spanning a range of memory_size. > > > > > > > > > > > > > > > > > > The extended memslot can still have the userspace_addr(hva). When use, a > > > > > > > > > single memslot can maintain both private memory through private > > > > > > > > > fd(private_fd/private_offset) and shared memory through > > > > > > > > > hva(userspace_addr). Whether the private or shared part is visible to > > > > > > > > > guest is maintained by other KVM code. > > > > > > > > > > > > > > > > What is anyway the appeal of private_offset field, instead of having just > > > > > > > > 1:1 association between regions and files, i.e. one memfd per region? > > > > > > > > > > > > Modifying memslots is slow, both in KVM and in QEMU (not sure about Google's VMM). > > > > > > E.g. if a vCPU converts a single page, it will be forced to wait until all other > > > > > > vCPUs drop SRCU, which can have severe latency spikes, e.g. if KVM is faulting in > > > > > > memory. KVM's memslot updates also hold a mutex for the entire duration of the > > > > > > update, i.e. conversions on different vCPUs would be fully serialized, exacerbating > > > > > > the SRCU problem. > > > > > > > > > > > > KVM also has historical baggage where it "needs" to zap _all_ SPTEs when any > > > > > > memslot is deleted. > > > > > > > > > > > > Taking both a private_fd and a shared userspace address allows userspace to convert > > > > > > between private and shared without having to manipulate memslots. > > > > > > > > > > Right, this was really good explanation, thank you. > > > > > > > > > > Still wondering could this possibly work (or not): > > > > > > > > > > 1. Union userspace_addr and private_fd. > > > > > > > > No, because userspace needs to be able to provide both userspace_addr (shared > > > > memory) and private_fd (private memory) for a single memslot. > > > > > > Got it, thanks for clearing my misunderstandings on this topic, and it > > > is quite obviously visible in 5/8 and 7/8. I.e. if I got it right, > > > memblock can be partially private, and you dig the shared holes with > > > KVM_MEMORY_ENCRYPT_UNREG_REGION. We have (in Enarx) ATM have memblock > > > per host mmap, I was looking into this dilated by that mindset but makes > > > definitely sense to support that. > > > > For me the most useful reference with this feature is kvm_set_phys_mem() > > implementation in privmem-v8 branch. Took while to find it because I did > > not have much experience with QEMU code base. I'd even recommend to mention > > that function in the cover letter because it is really good reference on > > how this feature is supposed to be used. That's a good point, I can mention that if people find useful. > > While learning QEMU code, I also noticed bunch of comparison like this: > > if (slot->flags | KVM_MEM_PRIVATE) > > I guess those could be just replaced with unconditional fills as it does > not do any harm, if KVM_MEM_PRIVATE is not set. Make sense, thanks. Chao > > BR, Jarkko