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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 71F7EC433F5 for ; Wed, 24 Nov 2021 05:08:07 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.229903.397698 (Exim 4.92) (envelope-from ) id 1mpkVV-0006a8-A3; Wed, 24 Nov 2021 05:07:45 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 229903.397698; Wed, 24 Nov 2021 05:07:45 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mpkVV-0006Zh-53; Wed, 24 Nov 2021 05:07:45 +0000 Received: by outflank-mailman (input) for mailman id 229903; Tue, 23 Nov 2021 18:13:40 +0000 Received: from se1-gles-sth1-in.inumbo.com ([159.253.27.254] helo=se1-gles-sth1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1mpaIW-0005KS-Sd for xen-devel@lists.xenproject.org; Tue, 23 Nov 2021 18:13:40 +0000 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by se1-gles-sth1.inumbo.com (Halon) with ESMTP id 14a584a7-4c89-11ec-9787-a32c541c8605; Tue, 23 Nov 2021 19:13:39 +0100 (CET) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BC8E71FB; Tue, 23 Nov 2021 10:13:37 -0800 (PST) Received: from e113632-lin (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7F59E3F5A1; Tue, 23 Nov 2021 10:13:35 -0800 (PST) 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" X-Inumbo-ID: 14a584a7-4c89-11ec-9787-a32c541c8605 From: Valentin Schneider To: Sebastian Andrzej Siewior , "Longpeng \(Mike\, Cloud Infrastructure Service Product Dept.\)" Cc: linux-kernel@vger.kernel.org, "Gonglei \(Arei\)" , x86@kernel.org, xen-devel@lists.xenproject.org, Peter Zijlstra , Ingo Molnar , Boris Ostrovsky , Juergen Gross , Stefano Stabellini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Subject: Re: [PATCH] cpu/hotplug: Allow the CPU in CPU_UP_PREPARE state to be brought up again. In-Reply-To: <20211122154714.xaoxok3fpk5bgznz@linutronix.de> References: <20211122154714.xaoxok3fpk5bgznz@linutronix.de> Date: Tue, 23 Nov 2021 18:13:30 +0000 Message-ID: <87r1b6d9kl.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain On 22/11/21 16:47, Sebastian Andrzej Siewior wrote: > From: "Longpeng(Mike)" > > A CPU will not show up in virtualized environment which includes an > Enclave. The VM splits its resources into a primary VM and a Enclave > VM. While the Enclave is active, the hypervisor will ignore all requests > to bring up a CPU and this CPU will remain in CPU_UP_PREPARE state. > The kernel will wait up to ten seconds for CPU to show up > (do_boot_cpu()) and then rollback the hotplug state back to > CPUHP_OFFLINE leaving the CPU state in CPU_UP_PREPARE. The CPU state is > set back to CPUHP_TEARDOWN_CPU during the CPU_POST_DEAD stage. > For my own education, this is talking about *host* CPU hotplug, right? > After the Enclave VM terminates, the primary VM can bring up the CPU > again. > > Allow to bring up the CPU if it is in the CPU_UP_PREPARE state. > > [bigeasy: Rewrite commit description.] > > Signed-off-by: Longpeng(Mike) > Signed-off-by: Sebastian Andrzej Siewior > Link: https://lore.kernel.org/r/20210901051143.2752-1-longpeng2@huawei.com > --- > > For XEN: this changes the behaviour as it allows to invoke > cpu_initialize_context() again should it have have earlier. I *think* > this is okay and would to bring up the CPU again should the memory > allocation in cpu_initialize_context() fail. Virt stuff notwithstanding, that looks OK to me. Reviewed-by: Valentin Schneider That said, AFAICT only powerpc makes actual use of the state being set to CPU_UP_PREPARE, it looks to be needless bookkeeping for everyone else (and there's archs that seem happy using only CPU_DEAD / CPU_POST_DEAD). > > kernel/smpboot.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/smpboot.c b/kernel/smpboot.c > index f6bc0bc8a2aab..34958d7fe2c1c 100644 > --- a/kernel/smpboot.c > +++ b/kernel/smpboot.c > @@ -392,6 +392,13 @@ int cpu_check_up_prepare(int cpu) > */ > return -EAGAIN; > > + case CPU_UP_PREPARE: > + /* > + * Timeout while waiting for the CPU to show up. Allow to try > + * again later. > + */ > + return 0; > + > default: > > /* Should not happen. Famous last words. */ > -- > 2.33.1