From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 8864B7D90D for ; Thu, 8 Aug 2019 15:49:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732845AbfHHPtt (ORCPT ); Thu, 8 Aug 2019 11:49:49 -0400 Received: from foss.arm.com ([217.140.110.172]:35216 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728380AbfHHPtt (ORCPT ); Thu, 8 Aug 2019 11:49:49 -0400 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 593D01596; Thu, 8 Aug 2019 08:49:48 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A5E283F706; Thu, 8 Aug 2019 08:49:46 -0700 (PDT) Subject: Re: [PATCH 9/9] arm64: Retrieve stolen time as paravirtualized guest To: Steven Price Cc: Catalin Marinas , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Russell King , Will Deacon , James Morse , Julien Thierry , Suzuki K Pouloze , kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190802145017.42543-1-steven.price@arm.com> <20190802145017.42543-10-steven.price@arm.com> <20190804105353.5e9824dc@why> From: Marc Zyngier Organization: Approximate Message-ID: <7108a70b-dafd-507b-8509-f4a092ef24af@kernel.org> Date: Thu, 8 Aug 2019 16:49:45 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 08/08/2019 16:29, Steven Price wrote: > On 04/08/2019 10:53, Marc Zyngier wrote: >> On Fri, 2 Aug 2019 15:50:17 +0100 >> Steven Price wrote: >> >>> Enable paravirtualization features when running under a hypervisor >>> supporting the PV_TIME_ST hypercall. >>> >>> For each (v)CPU, we ask the hypervisor for the location of a shared >>> page which the hypervisor will use to report stolen time to us. We set >>> pv_time_ops to the stolen time function which simply reads the stolen >>> value from the shared page for a VCPU. We guarantee single-copy >>> atomicity using READ_ONCE which means we can also read the stolen >>> time for another VCPU than the currently running one while it is >>> potentially being updated by the hypervisor. >>> >>> Signed-off-by: Steven Price >>> --- >>> arch/arm64/kernel/Makefile | 1 + >>> arch/arm64/kernel/kvm.c | 155 +++++++++++++++++++++++++++++++++++++ [...] >>> +static int __init kvm_guest_init(void) >>> +{ >>> + int ret = 0; >>> + >>> + if (!has_kvm_steal_clock()) >>> + return 0; >>> + >>> + ret = kvm_arm_init_stolen_time(); >>> + if (ret) >>> + return ret; >>> + >>> + pv_ops.time.steal_clock = kvm_steal_clock; >>> + >>> + static_key_slow_inc(¶virt_steal_enabled); >>> + if (steal_acc) >>> + static_key_slow_inc(¶virt_steal_rq_enabled); >>> + >>> + pr_info("using stolen time PV\n"); >>> + >>> + return 0; >>> +} >>> +early_initcall(kvm_guest_init); >> >> Is there any reason why we wouldn't directly call into this rather than >> using an initcall? > > I'm not sure where the direct call would go - any pointers? I'd be temped to say arch/arm64/kernel/time.c:time_init(), provided that there is no issue with the CPU hotplug lock (I remember hitting that a while ago). M. -- Jazz is not dead, it just smells funny...