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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7672CC433B4 for ; Thu, 6 May 2021 14:29:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 44AEB61289 for ; Thu, 6 May 2021 14:29:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234397AbhEFOaj (ORCPT ); Thu, 6 May 2021 10:30:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:57970 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234792AbhEFOai (ORCPT ); Thu, 6 May 2021 10:30:38 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 604F860E09; Thu, 6 May 2021 14:29:40 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lef0U-00BG3a-62; Thu, 06 May 2021 15:29:38 +0100 Date: Thu, 06 May 2021 15:29:37 +0100 Message-ID: <87o8doq6jy.wl-maz@kernel.org> From: Marc Zyngier To: Zenghui Yu Cc: , , , , Will Deacon , James Morse , Julien Thierry , Suzuki K Poulose , Andrew Scull , Mark Rutland , Quentin Perret , David Brazdil Subject: Re: [PATCH v2 03/11] KVM: arm64: Make kvm_skip_instr() and co private to HYP In-Reply-To: References: <20201102164045.264512-1-maz@kernel.org> <20201102164045.264512-4-maz@kernel.org> <875yzxnn5w.wl-maz@kernel.org> <87zgx8mkwd.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: yuzenghui@huawei.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, kernel-team@android.com, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, ascull@google.com, mark.rutland@arm.com, qperret@google.com, dbrazdil@google.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, 06 May 2021 12:43:26 +0100, Zenghui Yu wrote: > > On 2021/5/6 14:33, Marc Zyngier wrote: > > On Wed, 05 May 2021 17:46:51 +0100, > > Marc Zyngier wrote: > >> > >> Hi Zenghui, > >> > >> On Wed, 05 May 2021 15:23:02 +0100, > >> Zenghui Yu wrote: > >>> > >>> Hi Marc, > >>> > >>> On 2020/11/3 0:40, Marc Zyngier wrote: > >>>> In an effort to remove the vcpu PC manipulations from EL1 on nVHE > >>>> systems, move kvm_skip_instr() to be HYP-specific. EL1's intent > >>>> to increment PC post emulation is now signalled via a flag in the > >>>> vcpu structure. > >>>> > >>>> Signed-off-by: Marc Zyngier > >>> > >>> [...] > >>> > >>>> @@ -133,6 +134,8 @@ static int __kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu) > >>>> __load_guest_stage2(vcpu->arch.hw_mmu); > >>>> __activate_traps(vcpu); > >>>> + __adjust_pc(vcpu); > >>> > >>> If the INCREMENT_PC flag was set (e.g., for WFx emulation) while we're > >>> handling PSCI CPU_ON call targetting this VCPU, the *target_pc* (aka > >>> entry point address, normally provided by the primary VCPU) will be > >>> unexpectedly incremented here. That's pretty bad, I think. > >> > >> How can you online a CPU using PSCI if that CPU is currently spinning > >> on a WFI? Or is that we have transitioned via userspace to perform the > >> vcpu reset? I can imagine it happening in that case. > > I hadn't tried to reset VCPU from userspace. That would be a much easier > way to reproduce this problem. Then I don't understand how you end-up there. If the vcpu was in WFI, it wasn't off and PSCI_CPU_ON doesn't have any effect. > > Actually, this is far worse than it looks, and this only papers over > > one particular symptom. We need to resolve all pending PC updates > > *before* returning to userspace, or things like live migration can > > observe an inconsistent state. > > Ah yeah, agreed. > > Apart from the PC manipulation, I noticed that when handling the user > GET_VCPU_EVENTS request: > > | /* > | * We never return a pending ext_dabt here because we deliver it to > | * the virtual CPU directly when setting the event and it's no longer > | * 'pending' at this point. > | */ > > Which isn't true anymore now that we defer the exception injection right > before the VCPU entry. I believe the comment will be valid again once I fix the core issue, which is that we shouldn't return to userspace with pending PC adjustments. As long as KVM_GET_VCPU_EVENTS isn't issued on a running vcpu (which looks pointless to me), this should be just fine. Thanks, M. -- Without deviation from the norm, progress is not possible.