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=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 71BFCC433E9 for ; Tue, 2 Feb 2021 14:36:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3F84064F51 for ; Tue, 2 Feb 2021 14:36:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234676AbhBBOfq (ORCPT ); Tue, 2 Feb 2021 09:35:46 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:51205 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234620AbhBBOe3 (ORCPT ); Tue, 2 Feb 2021 09:34:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612276382; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=MOfLz2ooS1YVxqAqeLs03INDucXpuqKyLYasthASKR4=; b=UERma3UKTpOegbcM6USO7RvqJT6o1WZKHH1W1Kn10cFUe8SGQi43Yg9IDAMCQzl2OqZbZ+ IUovxp2eMpEgZI5ECZsnR8+Zf2sO5ZK24fle/+ym82euOD0aw8Lg1oLBpBI6AvlNiAtuhu rVw5wFRfKdsWNGcfevJ5XmRvMSUY+IU= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-586-QGq7qQrGPZmiYRqNjGj6Aw-1; Tue, 02 Feb 2021 09:33:00 -0500 X-MC-Unique: QGq7qQrGPZmiYRqNjGj6Aw-1 Received: by mail-wr1-f69.google.com with SMTP id u3so12572871wri.19 for ; Tue, 02 Feb 2021 06:33:00 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=MOfLz2ooS1YVxqAqeLs03INDucXpuqKyLYasthASKR4=; b=Dm0B+r9DcO+qfjqBZjwvy047U69v4xfMDeg+vMaAQsOFyvuI+7Lxi2l7tFXpJeHXC2 Tb/04suX87jfOXhBKT5Nc7ucMRCdZi1TSnsZt9Nt32gLnaExYfehClxW1VhxijBm3Efl tqwp2yHL56FIbnPP+MJOuWdEu7hCOxaheNjsX/6wqfO0DxS+Qja6C7LGtQgrwtDkMmpp eH+1J+79jGPFazqPGLIzIUxpNwi+luGYEvHeLPJm4tdsSa34ndw8wyOL4E9C2Lsjo6mZ IKUix7NpZU0OaLG2RTdzvch0/5cOYACQf9oTGor0WKQyv2XhlKX7Q9px2ubokJwmDAPh 2mxQ== X-Gm-Message-State: AOAM533fDrsrez3AX6vhlctTk4lpntWzNisM6DjbQZHJghpI0BEw8bsl 8fRNQUhYhvbuUmEPL37QdVkubPTARuMAIFlseOBFQKzQUZx/OvrrJqtlLOfw2ZQ2UqMK2MnBW7D 6EGaa/04yR6gN5sqhf+epTHOD X-Received: by 2002:adf:d1cb:: with SMTP id b11mr24388392wrd.118.1612276379287; Tue, 02 Feb 2021 06:32:59 -0800 (PST) X-Google-Smtp-Source: ABdhPJzNlKeX+el7cMOrZK5yq6RtSBJMhNR+o0snQl4QXFgxLrVEgd3S6vtJXgCeHmPNLUWxDwZ7tg== X-Received: by 2002:adf:d1cb:: with SMTP id b11mr24388360wrd.118.1612276379086; Tue, 02 Feb 2021 06:32:59 -0800 (PST) Received: from redhat.com (bzq-79-177-39-148.red.bezeqint.net. [79.177.39.148]) by smtp.gmail.com with ESMTPSA id b138sm3242759wmb.35.2021.02.02.06.32.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Feb 2021 06:32:54 -0800 (PST) Date: Tue, 2 Feb 2021 09:32:50 -0500 From: "Michael S. Tsirkin" To: Pavel Machek Cc: Adrian Catangiu , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org, gregkh@linuxfoundation.org, graf@amazon.com, arnd@arndb.de, ebiederm@xmission.com, rppt@kernel.org, 0x7f454c46@gmail.com, borntraeger@de.ibm.com, Jason@zx2c4.com, jannh@google.com, w@1wt.eu, colmmacc@amazon.com, luto@kernel.org, tytso@mit.edu, ebiggers@kernel.org, dwmw@amazon.co.uk, bonzini@gnu.org, sblbir@amazon.com, raduweis@amazon.com, corbet@lwn.net, mhocko@kernel.org, rafael@kernel.org, mpe@ellerman.id.au, areber@redhat.com, ovzxemul@gmail.com, avagin@gmail.com, ptikhomirov@virtuozzo.com, gil@azul.com, asmehra@redhat.com, dgunigun@redhat.com, vijaysun@ca.ibm.com, oridgar@gmail.com, ghammer@redhat.com Subject: Re: [PATCH v4 1/2] drivers/misc: sysgenid: add system generation id driver Message-ID: <20210202092418-mutt-send-email-mst@kernel.org> References: <1610453760-13812-1-git-send-email-acatan@amazon.com> <1610453760-13812-2-git-send-email-acatan@amazon.com> <20210127221505.GB24799@amd> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210127221505.GB24799@amd> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 27, 2021 at 11:15:05PM +0100, Pavel Machek wrote: > Hi! > > > - Solution > > > > The System Generation ID is a simple concept meant to alleviate the > > issue by providing a monotonically increasing u32 counter that changes > > each time the VM or container is restored from a snapshot. > > I'd make it u64. > > But as people explained, this has race problems that may be impossible > to solve? Well the read/write interface could be used in a safe way thinkably: - application checks VM gen id - application sends a transaction e.g. to database - application re-checks VM gen id - if id changed, application checks the database for duplicate transactions not sure how can the mmap interface be used safely. Drop it for now? > Best regards, > Pavel > > -- > http://www.livejournal.com/~pavelmachek 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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 85961C433E6 for ; Tue, 2 Feb 2021 14:44:31 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1959164ED7 for ; Tue, 2 Feb 2021 14:44:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1959164ED7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:51096 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l6wus-000556-2D for qemu-devel@archiver.kernel.org; Tue, 02 Feb 2021 09:44:30 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:45428) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l6wjq-0007lt-P8 for qemu-devel@nongnu.org; Tue, 02 Feb 2021 09:33:06 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:46317) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l6wjo-0005fa-Tv for qemu-devel@nongnu.org; Tue, 02 Feb 2021 09:33:06 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612276384; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=MOfLz2ooS1YVxqAqeLs03INDucXpuqKyLYasthASKR4=; b=fkp4KvtsAwTJnW0l8wYhfrP42SJuWM8LFePUnV/Bgw8XJKb7fTNRpL3m4qg7+rforVtgM/ d7XaJOscg1QQaGIfSjHKadrLwEJfXy3ezZWil2BYes07cQHVdTusPXp7denGBIGQT+ul5B df2ACjYASuvgOnD3Tc7djSitQNcSzJc= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-581-HXlLADSFPkCHQMzUz6-Xmw-1; Tue, 02 Feb 2021 09:33:00 -0500 X-MC-Unique: HXlLADSFPkCHQMzUz6-Xmw-1 Received: by mail-wr1-f71.google.com with SMTP id m7so1966524wro.12 for ; Tue, 02 Feb 2021 06:33:00 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=MOfLz2ooS1YVxqAqeLs03INDucXpuqKyLYasthASKR4=; b=KpLaiY/6t44I9IO+Qx2tTiv/ajerztzhiu98nWx/+l4y39pv2cBeO2jWy8HOP196f3 iFGcfFMDabkg/OOezHm3oVjxgWTOWtJByUGOAtM7U4CKFTn3xqY9WOX7cl+mcjafWWxV AUOE5Vyll3jb1EfKNNr5MQMMOjircbIpirIvNRa8n9Mmd1UMMzg+JGSIvds8MxZQXs8c V0wD/jC9lwZb+Jfs0wGJJpVNMY/INjs2QLLYy0tDXh8Xtqq4H8aa8q7/rANWtvuCOwYb ZckuIzkhy3htX0023prHNelu95kXeQPoeFQkDwXhdizOXNphjTGcWEV09YsMIDXV3T+6 WRhA== X-Gm-Message-State: AOAM531t2UaNzWfWQJt/YmAvd4dOhz2wXYPtlKj0YBssbvoKPKIozv6e Co9Mf1UaNDCnHkqW94UUrnyUaS9ebnvrn6/UPIqGX9dyVDhXi0ffMm5rX1mJuJIa73YQP2gmCON O68w23/hOaqO/bw8= X-Received: by 2002:adf:d1cb:: with SMTP id b11mr24388412wrd.118.1612276379289; Tue, 02 Feb 2021 06:32:59 -0800 (PST) X-Google-Smtp-Source: ABdhPJzNlKeX+el7cMOrZK5yq6RtSBJMhNR+o0snQl4QXFgxLrVEgd3S6vtJXgCeHmPNLUWxDwZ7tg== X-Received: by 2002:adf:d1cb:: with SMTP id b11mr24388360wrd.118.1612276379086; Tue, 02 Feb 2021 06:32:59 -0800 (PST) Received: from redhat.com (bzq-79-177-39-148.red.bezeqint.net. [79.177.39.148]) by smtp.gmail.com with ESMTPSA id b138sm3242759wmb.35.2021.02.02.06.32.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Feb 2021 06:32:54 -0800 (PST) Date: Tue, 2 Feb 2021 09:32:50 -0500 From: "Michael S. Tsirkin" To: Pavel Machek Subject: Re: [PATCH v4 1/2] drivers/misc: sysgenid: add system generation id driver Message-ID: <20210202092418-mutt-send-email-mst@kernel.org> References: <1610453760-13812-1-git-send-email-acatan@amazon.com> <1610453760-13812-2-git-send-email-acatan@amazon.com> <20210127221505.GB24799@amd> MIME-Version: 1.0 In-Reply-To: <20210127221505.GB24799@amd> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.386, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jason@zx2c4.com, dgunigun@redhat.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, ghammer@redhat.com, vijaysun@ca.ibm.com, 0x7f454c46@gmail.com, qemu-devel@nongnu.org, mhocko@kernel.org, oridgar@gmail.com, avagin@gmail.com, ptikhomirov@virtuozzo.com, linux-s390@vger.kernel.org, corbet@lwn.net, mpe@ellerman.id.au, rafael@kernel.org, ebiggers@kernel.org, borntraeger@de.ibm.com, sblbir@amazon.com, bonzini@gnu.org, arnd@arndb.de, jannh@google.com, raduweis@amazon.com, asmehra@redhat.com, Adrian Catangiu , graf@amazon.com, rppt@kernel.org, luto@kernel.org, gil@azul.com, colmmacc@amazon.com, tytso@mit.edu, gregkh@linuxfoundation.org, areber@redhat.com, linux-kernel@vger.kernel.org, ebiederm@xmission.com, ovzxemul@gmail.com, w@1wt.eu, dwmw@amazon.co.uk Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jan 27, 2021 at 11:15:05PM +0100, Pavel Machek wrote: > Hi! > > > - Solution > > > > The System Generation ID is a simple concept meant to alleviate the > > issue by providing a monotonically increasing u32 counter that changes > > each time the VM or container is restored from a snapshot. > > I'd make it u64. > > But as people explained, this has race problems that may be impossible > to solve? Well the read/write interface could be used in a safe way thinkably: - application checks VM gen id - application sends a transaction e.g. to database - application re-checks VM gen id - if id changed, application checks the database for duplicate transactions not sure how can the mmap interface be used safely. Drop it for now? > Best regards, > Pavel > > -- > http://www.livejournal.com/~pavelmachek