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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 816D2C3A59D for ; Thu, 22 Aug 2019 11:01:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5D8BA233A0 for ; Thu, 22 Aug 2019 11:01:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387983AbfHVLA7 (ORCPT ); Thu, 22 Aug 2019 07:00:59 -0400 Received: from foss.arm.com ([217.140.110.172]:43850 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731126AbfHVLA6 (ORCPT ); Thu, 22 Aug 2019 07:00:58 -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 D3F691596; Thu, 22 Aug 2019 04:00:57 -0700 (PDT) Received: from [10.1.196.133] (e112269-lin.cambridge.arm.com [10.1.196.133]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E5B673F246; Thu, 22 Aug 2019 04:00:55 -0700 (PDT) Subject: Re: [PATCH v3 05/10] KVM: arm64: Support stolen time reporting via shared structure To: Jonathan Cameron Cc: Mark Rutland , kvm@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Marc Zyngier , Suzuki K Pouloze , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Russell King , James Morse , Julien Thierry , Catalin Marinas , Paolo Bonzini , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org References: <20190821153656.33429-1-steven.price@arm.com> <20190821153656.33429-6-steven.price@arm.com> <20190822113942.0000701f@huawei.com> From: Steven Price Message-ID: <301610cc-ba04-89d6-a0b6-d37ecf4a717a@arm.com> Date: Thu, 22 Aug 2019 12:00:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190822113942.0000701f@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/08/2019 11:39, Jonathan Cameron wrote: > On Wed, 21 Aug 2019 16:36:51 +0100 > Steven Price wrote: > >> Implement the service call for configuring a shared structure between a >> VCPU and the hypervisor in which the hypervisor can write the time >> stolen from the VCPU's execution time by other tasks on the host. >> >> The hypervisor allocates memory which is placed at an IPA chosen by user >> space. The hypervisor then updates the shared structure using >> kvm_put_guest() to ensure single copy atomicity of the 64-bit value >> reporting the stolen time in nanoseconds. >> >> Whenever stolen time is enabled by the guest, the stolen time counter is >> reset. >> >> The stolen time itself is retrieved from the sched_info structure >> maintained by the Linux scheduler code. We enable SCHEDSTATS when >> selecting KVM Kconfig to ensure this value is meaningful. >> >> Signed-off-by: Steven Price > > One totally trivial comment inline... Feel free to ignore :) > [...] >> +int kvm_hypercall_stolen_time(struct kvm_vcpu *vcpu) >> +{ >> + u64 ret; >> + int err; >> + >> + /* >> + * Start counting stolen time from the time the guest requests >> + * the feature enabled. >> + */ >> + vcpu->arch.steal.steal = 0; >> + vcpu->arch.steal.last_steal = current->sched_info.run_delay; >> + >> + err = kvm_update_stolen_time(vcpu, true); >> + >> + if (err) >> + ret = SMCCC_RET_NOT_SUPPORTED; > > Trivial by why not > return SMCCC_RET_NOT_SUPPORTED; > > return vcpu->kvm->arch.pvtime.st_base + > ... > Drops the indentation a bit and puts the error handling out of > line which is slightly nicer to read (to my eyes). Yes that's a nice change - drops the extra "ret" variable too. Thanks, Steve