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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 EA401C4360C for ; Fri, 4 Oct 2019 09:13:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AEC8720867 for ; Fri, 4 Oct 2019 09:13:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731203AbfJDJNo (ORCPT ); Fri, 4 Oct 2019 05:13:44 -0400 Received: from foss.arm.com ([217.140.110.172]:39618 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725958AbfJDJNo (ORCPT ); Fri, 4 Oct 2019 05:13:44 -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 7066C1597; Fri, 4 Oct 2019 02:13:43 -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 5FCE83F739; Fri, 4 Oct 2019 02:13:41 -0700 (PDT) Subject: Re: [PATCH v5 05/10] KVM: arm64: Support stolen time reporting via shared structure To: Andrew Jones Cc: Marc Zyngier , Will Deacon , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, Catalin Marinas , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Russell King , James Morse , Julien Thierry , Suzuki K Pouloze , Mark Rutland , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20191002145037.51630-1-steven.price@arm.com> <20191002145037.51630-6-steven.price@arm.com> <20191003132235.ruanyfmdim5s6npj@kamzik.brq.redhat.com> <20191004070301.d7ari5rjlu3uuara@kamzik.brq.redhat.com> From: Steven Price Message-ID: Date: Fri, 4 Oct 2019 10:13:40 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191004070301.d7ari5rjlu3uuara@kamzik.brq.redhat.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 04/10/2019 08:03, Andrew Jones wrote: > On Thu, Oct 03, 2019 at 03:22:35PM +0200, Andrew Jones wrote: >> On Wed, Oct 02, 2019 at 03:50:32PM +0100, Steven Price wrote: >>> +int kvm_update_stolen_time(struct kvm_vcpu *vcpu, bool init) >>> +{ >>> + struct kvm *kvm = vcpu->kvm; >>> + u64 steal; >>> + u64 steal_le; >>> + u64 offset; >>> + int idx; >>> + u64 base = vcpu->arch.steal.base; >>> + >>> + if (base == GPA_INVALID) >>> + return -ENOTSUPP; >>> + >>> + /* Let's do the local bookkeeping */ >>> + steal = vcpu->arch.steal.steal; >>> + steal += current->sched_info.run_delay - vcpu->arch.steal.last_steal; >>> + vcpu->arch.steal.last_steal = current->sched_info.run_delay; >>> + vcpu->arch.steal.steal = steal; >>> + >>> + steal_le = cpu_to_le64(steal); >> >> Agreeing on a byte order for this interface makes sense, but I don't see >> it documented anywhere. Is this an SMCCC thing? Because I skimmed some >> of those specs and other users too but didn't see anything obvious. Anyway >> even if everybody but me knows that all data returned from SMCCC calls >> should be LE, it might be nice to document that in the pvtime doc. A very good point - I'll document this in the Linux document and feed that back for DEN0057A. > > I have another [potentially dumb] SMCCC byte order question. If we need > to worry about using LE for the members of this structure, then why don't > we need to worry about the actual return values of the SMCCC calls? Like > the IPA of the structure? The SMCCC calls pass values in registers. It's only when reading/writing these values from/to memory that the endianness actually has any meaning. Steve