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 7504AC433E0 for ; Wed, 20 Jan 2021 15:58:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1DDAC2339D for ; Wed, 20 Jan 2021 15:58:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733192AbhATP6A (ORCPT ); Wed, 20 Jan 2021 10:58:00 -0500 Received: from foss.arm.com ([217.140.110.172]:41362 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730476AbhATP5r (ORCPT ); Wed, 20 Jan 2021 10:57:47 -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 310691063; Wed, 20 Jan 2021 07:57:01 -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 A00BF3F68F; Wed, 20 Jan 2021 07:56:59 -0800 (PST) Subject: Re: [PATCH 5/9] KVM: arm: move has_run_once after the map_resources To: Auger Eric , 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> <0c9976a3-12ae-29b2-1f26-06ee52aa2ffe@arm.com> <3465e1e4-d202-ae36-5b61-87f796432428@redhat.com> From: Alexandru Elisei Message-ID: <5590800f-f77d-52e1-e408-c1afe4e284a2@arm.com> Date: Wed, 20 Jan 2021 15:56:34 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <3465e1e4-d202-ae36-5b61-87f796432428@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hi Eric, On 1/14/21 10:02 AM, Auger Eric wrote: > Hi Alexandru, > > On 1/12/21 3:55 PM, Alexandru Elisei wrote: >> 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. > Setting has_run_once = true at the entry of the function looks to me > even more arbitrary. I agree with you that eventually has_run_once may Or it could be it's there to prevent the user from calling kvm_vgic_map_resources() a second time after it failed. This is what I'm concerned about and I think deserves more investigation. Thanks, Alex > be moved at the very end but maybe this can be done later once timer, > pmu tests haven ben written >> 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() > I changed the commit msg so that "incorrect user settings" sounds as an > example. >> 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? > I think additional tests will confirm this. However at the moment, > moving the assignment, which does not look wrong to me, allows to > greatly simplify the tests so I would tend to say that it is worth. >> (*) 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? > doesn't kvm_io_bus_cmp() do the check? > > Thanks > > Eric >> Thanks, >> Alex >>> + >>> ret = kvm_timer_enable(vcpu); >>> if (ret) >>> return ret;