From patchwork Wed Jun 24 14:54:57 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Zyngier X-Patchwork-Id: 6668401 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 718529F380 for ; Wed, 24 Jun 2015 14:55:17 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 9E804204FC for ; Wed, 24 Jun 2015 14:55:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 75FC2204EA for ; Wed, 24 Jun 2015 14:55:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753540AbbFXOzL (ORCPT ); Wed, 24 Jun 2015 10:55:11 -0400 Received: from foss.arm.com ([217.140.101.70]:54262 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752985AbbFXOzK (ORCPT ); Wed, 24 Jun 2015 10:55:10 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E88BC2A; Wed, 24 Jun 2015 07:55:32 -0700 (PDT) Received: from approximate.cambridge.arm.com (approximate.cambridge.arm.com [10.1.209.148]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C15773F23A; Wed, 24 Jun 2015 07:55:08 -0700 (PDT) From: Marc Zyngier To: kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org Cc: Christoffer Dall , Peter Maydell Subject: [RFC PATCH] KVM: arm/arm64: Don't let userspace update CNTVOFF once guest is running Date: Wed, 24 Jun 2015 15:54:57 +0100 Message-Id: <1435157697-28579-1-git-send-email-marc.zyngier@arm.com> X-Mailer: git-send-email 2.1.4 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-8.3 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Userspace is allowed to set the guest's view of CNTVCT, which turns into setting CNTVOFF for the whole VM. One thing userspace is not supposed to do is to update that register while the guest is running. Time will either move forward (best case) or backward (really bad idea). Either way, this shouldn't happen. This patch prevents userspace from touching CNTVOFF as soon as a vcpu has been started. This ensures that time will keep monotonically increase. Signed-off-by: Marc Zyngier --- QEMU seems to trigger this at boot time, and I have no idea why it does so. It would be good to find out, hence the RFC tag. virt/kvm/arm/arch_timer.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c index 98c95f2..660f348 100644 --- a/virt/kvm/arm/arch_timer.c +++ b/virt/kvm/arm/arch_timer.c @@ -220,9 +220,26 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *vcpu, u64 regid, u64 value) case KVM_REG_ARM_TIMER_CTL: timer->cntv_ctl = value; break; - case KVM_REG_ARM_TIMER_CNT: - vcpu->kvm->arch.timer.cntvoff = kvm_phys_timer_read() - value; + case KVM_REG_ARM_TIMER_CNT: { + struct kvm_vcpu *tmp; + int i; + u64 cntvoff = kvm_phys_timer_read() - value; + + /* + * If any of the vcpus has started, don't update + * CNTVOFF. Userspace is severely brain damaged. + */ + kvm_for_each_vcpu(i, tmp, vcpu->kvm) { + if (tmp->arch.has_run_once) { + kvm_debug("Won't set CNTVOFF to %llx (%llx)\n", + cntvoff, + vcpu->kvm->arch.timer.cntvoff); + return -1; + } + } + vcpu->kvm->arch.timer.cntvoff = cntvoff; break; + } case KVM_REG_ARM_TIMER_CVAL: timer->cntv_cval = value; break;