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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 A3C8CC433DB for ; Tue, 12 Jan 2021 14:56:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6558B221EC for ; Tue, 12 Jan 2021 14:56:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732921AbhALO4i (ORCPT ); Tue, 12 Jan 2021 09:56:38 -0500 Received: from foss.arm.com ([217.140.110.172]:47732 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725846AbhALO4h (ORCPT ); Tue, 12 Jan 2021 09:56:37 -0500 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 06BCA11B3; Tue, 12 Jan 2021 06:55:52 -0800 (PST) Received: from [192.168.0.110] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6616C3F719; Tue, 12 Jan 2021 06:55:50 -0800 (PST) Subject: Re: [PATCH 5/9] KVM: arm: move has_run_once after the map_resources To: Eric Auger , eric.auger.pro@gmail.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, maz@kernel.org, drjones@redhat.com Cc: james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, shuah@kernel.org, pbonzini@redhat.com References: <20201212185010.26579-1-eric.auger@redhat.com> <20201212185010.26579-6-eric.auger@redhat.com> From: Alexandru Elisei Message-ID: <0c9976a3-12ae-29b2-1f26-06ee52aa2ffe@arm.com> Date: Tue, 12 Jan 2021 14:55:49 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20201212185010.26579-6-eric.auger@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Eric, On 12/12/20 6:50 PM, Eric Auger wrote: > has_run_once is set to true at the beginning of > kvm_vcpu_first_run_init(). This generally is not an issue > except when exercising the code with KVM selftests. Indeed, > if kvm_vgic_map_resources() fails due to erroneous user settings, > has_run_once is set and this prevents from continuing > executing the test. This patch moves the assignment after the > kvm_vgic_map_resources(). > > Signed-off-by: Eric Auger > --- > arch/arm64/kvm/arm.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index c0ffb019ca8b..331fae6bff31 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -540,8 +540,6 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu) > if (!kvm_arm_vcpu_is_finalized(vcpu)) > return -EPERM; > > - vcpu->arch.has_run_once = true; > - > if (likely(irqchip_in_kernel(kvm))) { > /* > * Map the VGIC hardware resources before running a vcpu the > @@ -560,6 +558,8 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu) > static_branch_inc(&userspace_irqchip_in_use); > } > > + vcpu->arch.has_run_once = true; I have a few concerns regarding this: 1. Moving has_run_once = true here seems very arbitrary to me - kvm_timer_enable() and kvm_arm_pmu_v3_enable(), below it, can both fail because of erroneous user values. If there's a reason why the assignment cannot be moved at the end of the function, I think it should be clearly stated in a comment for the people who might be tempted to write similar tests for the timer or pmu. 2. There are many ways that kvm_vgic_map_resources() can fail, other than incorrect user settings. I started digging into how kvm_vgic_map_resources()->vgic_v2_map_resources() can fail for a VGIC V2 and this is what I managed to find before I gave up: * vgic_init() can fail in:     - kvm_vgic_dist_init()     - vgic_v3_init()     - kvm_vgic_setup_default_irq_routing() * vgic_register_dist_iodev() can fail in:     - vgic_v3_init_dist_iodev()     - kvm_io_bus_register_dev()(*) * kvm_phys_addr_ioremap() can fail in:     - kvm_mmu_topup_memory_cache()     - kvm_pgtable_stage2_map() So if any of the functions below fail, are we 100% sure it is safe to allow the user to execute kvm_vgic_map_resources() again? (*) It looks to me like kvm_io_bus_register_dev() doesn't take into account a caller that tries to register the same device address range and it will create another identical range. Is this intentional? Is it a bug that should be fixed? Or am I misunderstanding the function? Thanks, Alex > + > ret = kvm_timer_enable(vcpu); > if (ret) > return ret;