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 X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10D8EC433EF for ; Fri, 3 Sep 2021 19:15:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 95063610CF for ; Fri, 3 Sep 2021 19:15:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 95063610CF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 3299B900002; Fri, 3 Sep 2021 15:15:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2D7F16B0072; Fri, 3 Sep 2021 15:15:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1C735900002; Fri, 3 Sep 2021 15:15:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0231.hostedemail.com [216.40.44.231]) by kanga.kvack.org (Postfix) with ESMTP id 0F5E46B0071 for ; Fri, 3 Sep 2021 15:15:55 -0400 (EDT) Received: from smtpin32.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id C24642BC01 for ; Fri, 3 Sep 2021 19:15:54 +0000 (UTC) X-FDA: 78547217028.32.137353D Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf10.hostedemail.com (Postfix) with ESMTP id 615526001988 for ; Fri, 3 Sep 2021 19:15:54 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 7F02D6108E; Fri, 3 Sep 2021 19:15:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1630696553; bh=BQ3atOGhagTKS/jN7T713TGmkTc5TaJTIHbqNKYO/50=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=k6URnp4SjueEReYTy8ipceiKt2Iy8AMtOH2L86uJVbhax1HCxnW4gA99NYB6DWHIk 9Joe/Nh3PSoX22fk4xBAlSDjCDBYg/9vfRgaeUd+tnGr40r6n3m3h6bifEQyjEue7E hfftaBQgviQPMqvuPzzkY/R7gY8+7OfBK9hCJqBun6NyAvWZrir7Hqnlpm8yf989xc JzzX1MK3uSOJUdF32phEGbtKZNdQYouK38mhHIgYTnzhOK3zmTI6lMJfJWH+lxAKgM WW8s53fcoPLqgAAD+19j3gGemnwqs2uR5aAnqLUwJBH54L30wzHLnPau9HNDFbqlDp fA/ONeF3QZeKg== Subject: Re: [RFC] KVM: mm: fd-based approach for supporting KVM guest private memory To: "Kirill A. Shutemov" , Sean Christopherson Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Borislav Petkov , Andrew Morton , Joerg Roedel , Andi Kleen , David Rientjes , Vlastimil Babka , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Varad Gautam , Dario Faggioli , x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, "Kirill A . Shutemov" , Kuppuswamy Sathyanarayanan , David Hildenbrand , Dave Hansen , Yu Zhang References: <20210824005248.200037-1-seanjc@google.com> <20210902184711.7v65p5lwhpr2pvk7@box.shutemov.name> <20210903191414.g7tfzsbzc7tpkx37@box.shutemov.name> From: Andy Lutomirski Message-ID: <02806f62-8820-d5f9-779c-15c0e9cd0e85@kernel.org> Date: Fri, 3 Sep 2021 12:15:51 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210903191414.g7tfzsbzc7tpkx37@box.shutemov.name> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=k6URnp4S; spf=pass (imf10.hostedemail.com: domain of luto@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=luto@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 615526001988 X-Stat-Signature: r54tiut9c6bt7j5739pxkhfs3mtaw9nj X-HE-Tag: 1630696554-375326 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 9/3/21 12:14 PM, Kirill A. Shutemov wrote: > On Thu, Sep 02, 2021 at 08:33:31PM +0000, Sean Christopherson wrote: >> Would requiring the size to be '0' at F_SEAL_GUEST time solve that problem? > > I guess. Maybe we would need a WRITE_ONCE() on set. I donno. I will look > closer into locking next. We can decisively eliminate this sort of failure by making the switch happen at open time instead of after. For a memfd-like API, this would be straightforward. For a filesystem, it would take a bit more thought.