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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A7CA6C433EF for ; Tue, 2 Nov 2021 16:01:50 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 6B15E61101 for ; Tue, 2 Nov 2021 16:01:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6B15E61101 Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=xenproject.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.220401.381681 (Exim 4.92) (envelope-from ) id 1mhwDm-0008U9-RA; Tue, 02 Nov 2021 16:01:10 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 220401.381681; Tue, 02 Nov 2021 16:01:10 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mhwDm-0008U2-OF; Tue, 02 Nov 2021 16:01:10 +0000 Received: by outflank-mailman (input) for mailman id 220401; Tue, 02 Nov 2021 16:01:09 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mhwDl-0008Tw-8y for xen-devel@lists.xenproject.org; Tue, 02 Nov 2021 16:01:09 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mhwDl-0000nT-3t for xen-devel@lists.xenproject.org; Tue, 02 Nov 2021 16:01:09 +0000 Received: from iwj (helo=mariner.uk.xensource.com) by xenbits.xenproject.org with local-bsmtp (Exim 4.92) (envelope-from ) id 1mhwDl-0003TQ-3E for xen-devel@lists.xenproject.org; Tue, 02 Nov 2021 16:01:09 +0000 Received: from iwj by mariner.uk.xensource.com with local (Exim 4.89) (envelope-from ) id 1mhwDU-0001Za-O9; Tue, 02 Nov 2021 16:00:52 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xenproject.org; s=20200302mail; h=References:In-Reply-To:Subject:Cc:To:Date :Message-ID:Content-Transfer-Encoding:Content-Type:MIME-Version:From; bh=Dai0H+tuPEb1tkqZ47Fy88yw9gcbx1FydiV2M5UUips=; b=dPfNmedWbD6vKhDLqw0GYvbMuQ 2vH83QWGnKtzozYIFQF1Hn+pHa1mh7l8gYuDJ/cCVE/X+yqf7rti7/j8pwthI4mLDgEqF0U4cBMKQ WxBdtSarmO++mFTIpfKJvpvIwd4EOa6P8wJDrQY0JI7EyjB+9S3DSwssWH/JKzN66o8I=; From: Ian Jackson MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <24961.24756.236341.888900@mariner.uk.xensource.com> Date: Tue, 2 Nov 2021 16:00:52 +0000 To: Jan Beulich Cc: Dongli Zhang , sstabellini@kernel.org, julien@xen.org, Volodymyr_Babchuk@epam.com, andrew.cooper3@citrix.com, george.dunlap@citrix.com, wl@xen.org, joe.jin@oracle.com, xen-devel@lists.xenproject.org Subject: Re: [PATCH v2 1/1] xen: update system time immediately when VCPUOP_register_vcpu_info In-Reply-To: References: <20211025173523.3647-1-dongli.zhang@oracle.com> X-Mailer: VM 8.2.0b under 24.5.1 (i686-pc-linux-gnu) Jan Beulich writes ("Re: [PATCH v2 1/1] xen: update system time immediately when VCPUOP_register_vcpu_info"): > On 25.10.2021 19:35, Dongli Zhang wrote: > > The guest may access the pv vcpu_time_info immediately after > > VCPUOP_register_vcpu_info. This is to borrow the idea of > > VCPUOP_register_vcpu_time_memory_area, where the > > force_update_vcpu_system_time() is called immediately when the new memory > > area is registered. > > > > Otherwise, we may observe clock drift at the VM side if the VM accesses > > the clocksource immediately after VCPUOP_register_vcpu_info(). > > > > Reference: > > https://lists.xenproject.org/archives/html/xen-devel/2021-10/msg00571.html > > Cc: Joe Jin > > Signed-off-by: Dongli Zhang > > Reviewed-by: Jan Beulich > > Ian - any thoughts towards 4.16 here either way? This looks like a bugfix to me, and the diff is certainly small. I am positively inclined. I would like to know what the risks are. Stefano says this does nothing on ARM so the risk would be to x86. Can you advise ? Thanks, Ian.