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 14C23C4321E for ; Wed, 12 Oct 2022 08:14:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6BB716B0071; Wed, 12 Oct 2022 04:14:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 66B286B0073; Wed, 12 Oct 2022 04:14:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 50B9B900002; Wed, 12 Oct 2022 04:14:32 -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 38DDE6B0071 for ; Wed, 12 Oct 2022 04:14:32 -0400 (EDT) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id EF3291A106F for ; Wed, 12 Oct 2022 08:14:31 +0000 (UTC) X-FDA: 80011585542.29.CEE3D39 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf27.hostedemail.com (Postfix) with ESMTP id 62E5D40026 for ; Wed, 12 Oct 2022 08:14:30 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id A8A2EB819B5; Wed, 12 Oct 2022 08:14:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF244C433D6; Wed, 12 Oct 2022 08:14:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1665562467; bh=LztmwvXdNCm1f+34a+megCcYhhpdDqS6aiTmicYdPF8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kleJYJtMEas4yS4RIXkTvXxxmFB47lcONJVV4sKjv+gcua2rPdtmCSedjkBabAc5b hURHMNdHWx7r4wowISznvsizi5Im+t49R31DXBrxGFTPbODdfTQ45XZDHhKYo+JvHL t6QsJW8EDjUc9rhZsiuHIKhUNbaOtRdEwyO+hSXYPGCmYEKpWNusDs75tgGv3i7DGB Cabm5X3AcR4lCdWi6S4ohFHrXaIkXFb5OiLHlboF0GIBH8p74FABaO+Qze8RI5WE1J AOOcOtKMetuPMcewlepYLN3mlBduTOUDyUr3WWYASoOrEnFMPOJaqW2LeRPKXF8rL8 D1OfYmz8/fNBA== Date: Wed, 12 Oct 2022 11:14:24 +0300 From: Jarkko Sakkinen To: Chao Peng 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: References: <20220915142913.2213336-3-chao.p.peng@linux.intel.com> <20221010082507.GA3144879@chaop.bj.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221010082507.GA3144879@chaop.bj.intel.com> ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=kleJYJtM; spf=pass (imf27.hostedemail.com: domain of jarkko@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=jarkko@kernel.org; dmarc=pass (policy=none) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1665562470; a=rsa-sha256; cv=none; b=iD4MsyZA9AOzx81maLeFTSrEVTH2qS70qbW3F2pVfPvufiZ2seI/Lb7cLbLYOHkoHbo0Z6 B8I7MAWQXnNswizcY9Fjyt2gBNoho4oW31+2gjEFH/KLsYxNCHpj1DJGv8Gf5rp2OtAjjt UPC61CSfCSi+bt47ydbvsIu4/Wmrtl0= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1665562470; 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=UykTJ8CCHrVodFVhG+pHMmXqqKcWQVVQmCxVhpiykbc=; b=aE4mLJJ65s8yJmhHDvybjLoZv1IuXaNYZlBeVgl29bkxRYGSq9xbC+8+66XYyB7yofzo2h xblY5tGSjiPpw1MSUuJrrMVHdoakcs2kug7EegEhxDIf+nn3Uv6RYNMsocDHn6rJktqmUX 550+wVfiZhE9qwRYlX/IaZpyyj0x0Fg= X-Rspamd-Server: rspam05 X-Rspam-User: Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=kleJYJtM; spf=pass (imf27.hostedemail.com: domain of jarkko@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=jarkko@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-Stat-Signature: e9one6ncwpfwa6ydx7rh6td8spf38nyw X-Rspamd-Queue-Id: 62E5D40026 X-HE-Tag: 1665562470-383008 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 Mon, Oct 10, 2022 at 04:25:07PM +0800, Chao Peng wrote: > 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. Yeah, I did implementation for Enarx (https://www.enarx.dev/) using just that part as a reference. It has all the essentials what you need to consider when you are already using KVM API, and want to add private regions. BR, Jarkko