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[34.168.104.7]) by smtp.gmail.com with ESMTPSA id e14-20020a63db0e000000b0042c2def703asm7191167pgg.22.2022.09.13.02.44.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Sep 2022 02:44:31 -0700 (PDT) Date: Tue, 13 Sep 2022 09:44:27 +0000 From: Sean Christopherson To: "Kirill A. Shutemov" Cc: "Kirill A . Shutemov" , Hugh Dickins , Chao Peng , 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" , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , 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 , "Gupta, Pankaj" , Elena Reshetova Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory Message-ID: References: <20220706082016.2603916-1-chao.p.peng@linux.intel.com> <20220818132421.6xmjqduempmxnnu2@box> <20220820002700.6yflrxklmpsavdzi@box.shutemov.name> <20220831142439.65q2gi4g2d2z4ofh@box.shutemov.name> <20220908011037.ez2cdorthqxkerwk@box.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220908011037.ez2cdorthqxkerwk@box.shutemov.name> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663062273; a=rsa-sha256; cv=none; b=hCPGtexX8C4S2POofxoMcizAGsvhj+1K2M5zbY/B+6/56+8lkgmVSODaXQHGDOaCYVkaYY td+JuNF0PWzychBpR2jDsBjceqltWtQsqussT6HYu4Ac1ygZhim7E1WoSiOzXs1Fp33I7b bWmjZE6RFhOjb9Eo/Y+n5JwbBr6ALvw= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b="kjd/plfm"; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf06.hostedemail.com: domain of seanjc@google.com designates 209.85.210.182 as permitted sender) smtp.mailfrom=seanjc@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663062273; 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=ZmfmFbMYmaq0ZyQMdMN01+8jHfJN0luS93tqSO/DBY4=; b=KR4qZ4ppxoDh8qG1ik4kVnJzZdWQJXtmaYuBC8lBjPwbMIHf0Y2IYYjHuU6hIAsCdPrjFh cCJzE39HnyQMIOG3Y+FmPAaSTLDk20gp1bp2EDTPIr8tQ//iY+xKidemAWKCQJL8IIjaw2 uGubxdq3lDkHBc3BOeG57ROvNhejfcs= Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b="kjd/plfm"; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf06.hostedemail.com: domain of seanjc@google.com designates 209.85.210.182 as permitted sender) smtp.mailfrom=seanjc@google.com X-Rspam-User: X-Rspamd-Server: rspam06 X-Stat-Signature: 9hgtfurta6kdk9d3s3njt6qten94f4h5 X-Rspamd-Queue-Id: 088EF180087 X-HE-Tag: 1663062272-127612 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, Sep 08, 2022, Kirill A. Shutemov wrote: > On Wed, Aug 31, 2022 at 05:24:39PM +0300, Kirill A . Shutemov wrote: > > On Sat, Aug 20, 2022 at 10:15:32PM -0700, Hugh Dickins wrote: > > > > I will try next week to rework it as shim to top of shmem. Does it work > > > > for you? > > > > > > Yes, please do, thanks. It's a compromise between us: the initial TDX > > > case has no justification to use shmem at all, but doing it that way > > > will help you with some of the infrastructure, and will probably be > > > easiest for KVM to extend to other more relaxed fd cases later. > > > > Okay, below is my take on the shim approach. > > > > I don't hate how it turned out. It is easier to understand without > > callback exchange thing. > > > > The only caveat is I had to introduce external lock to protect against > > race between lookup and truncate. As before, I think this lock is unnecessary. Or at least it's unnessary to hold the lock across get/put. The ->invalidate() call will ensure that the pfn is never actually used if get() races with truncation. Switching topics, what actually prevents mmapp() on the shim? I tried to follow, but I don't know these areas well enough.