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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 54F15C41536 for ; Tue, 20 Nov 2018 17:22:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0657E20685 for ; Tue, 20 Nov 2018 17:22:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0657E20685 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730383AbeKUDw5 (ORCPT ); Tue, 20 Nov 2018 22:52:57 -0500 Received: from foss.arm.com ([217.140.101.70]:57798 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726314AbeKUDw5 (ORCPT ); Tue, 20 Nov 2018 22:52:57 -0500 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 3584E1DC8; Tue, 20 Nov 2018 09:22:43 -0800 (PST) Received: from [10.1.197.36] (e112298-lin.cambridge.arm.com [10.1.197.36]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 882593F5AF; Tue, 20 Nov 2018 09:22:41 -0800 (PST) Subject: Re: [PATCH 1/4] KVM: arm/arm64: vgic: Do not cond_resched_lock() with IRQs disabled To: Christoffer Dall Cc: linux-kernel@vger.kernel.org, kvmarm@lists.cs.columbia.edu, marc.zyngier@arm.com, linux-arm-kernel@lists.infradead.org, linux-rt-users@vger.kernel.org, tglx@linutronix.de, rostedt@goodmis.org, bigeasy@linutronix.de, stable@vger.kernel.org References: <1542647279-46609-1-git-send-email-julien.thierry@arm.com> <1542647279-46609-2-git-send-email-julien.thierry@arm.com> <20181120141832.GA11162@e113682-lin.lund.arm.com> From: Julien Thierry Message-ID: <76a488a9-893c-ffbe-16f2-23735af8126a@arm.com> Date: Tue, 20 Nov 2018 17:22:39 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20181120141832.GA11162@e113682-lin.lund.arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/11/18 14:18, Christoffer Dall wrote: > On Mon, Nov 19, 2018 at 05:07:56PM +0000, Julien Thierry wrote: >> To change the active state of an MMIO, halt is requested for all vcpus of >> the affected guest before modifying the IRQ state. This is done by calling >> cond_resched_lock() in vgic_mmio_change_active(). However interrupts are >> disabled at this point and running a vcpu cannot get rescheduled. > > "running a vcpu cannot get rescheduled" ? Yes, that doesn't make much sense :\ . I guess I just meant "a vcpu cannot get rescheduled on this cpu". I'll rewrite this. > >> >> Solve this by waiting for all vcpus to be halted after emmiting the halt >> request. >> >> Fixes commit 6c1b7521f4a07cc63bbe2dfe290efed47cdb780a ("KVM: arm/arm64: >> Factor out functionality to get vgic mmio requester_vcpu") >> >> Signed-off-by: Julien Thierry >> Suggested-by: Marc Zyngier >> Cc: Christoffer Dall >> Cc: Marc Zyngier >> Cc: stable@vger.kernel.org >> --- >> virt/kvm/arm/vgic/vgic-mmio.c | 33 +++++++++++---------------------- >> 1 file changed, 11 insertions(+), 22 deletions(-) >> >> diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c >> index f56ff1c..eefd877 100644 >> --- a/virt/kvm/arm/vgic/vgic-mmio.c >> +++ b/virt/kvm/arm/vgic/vgic-mmio.c >> @@ -313,27 +313,6 @@ static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq, >> >> spin_lock_irqsave(&irq->irq_lock, flags); >> >> - /* >> - * If this virtual IRQ was written into a list register, we >> - * have to make sure the CPU that runs the VCPU thread has >> - * synced back the LR state to the struct vgic_irq. >> - * >> - * As long as the conditions below are true, we know the VCPU thread >> - * may be on its way back from the guest (we kicked the VCPU thread in >> - * vgic_change_active_prepare) and still has to sync back this IRQ, >> - * so we release and re-acquire the spin_lock to let the other thread >> - * sync back the IRQ. >> - * >> - * When accessing VGIC state from user space, requester_vcpu is >> - * NULL, which is fine, because we guarantee that no VCPUs are running >> - * when accessing VGIC state from user space so irq->vcpu->cpu is >> - * always -1. >> - */ >> - while (irq->vcpu && /* IRQ may have state in an LR somewhere */ >> - irq->vcpu != requester_vcpu && /* Current thread is not the VCPU thread */ >> - irq->vcpu->cpu != -1) /* VCPU thread is running */ >> - cond_resched_lock(&irq->irq_lock); >> - >> if (irq->hw) { >> vgic_hw_irq_change_active(vcpu, irq, active, !requester_vcpu); >> } else { >> @@ -368,8 +347,18 @@ static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq, >> */ >> static void vgic_change_active_prepare(struct kvm_vcpu *vcpu, u32 intid) >> { >> - if (intid > VGIC_NR_PRIVATE_IRQS) >> + if (intid > VGIC_NR_PRIVATE_IRQS) { >> + struct kvm_vcpu *tmp; >> + int i; >> + >> kvm_arm_halt_guest(vcpu->kvm); >> + >> + /* Wait for each vcpu to be halted */ >> + kvm_for_each_vcpu(i, tmp, vcpu->kvm) { >> + while (tmp->cpu != -1) >> + cond_resched(); > > We used to have something like this which Andre then found out it could > deadlock the system, because the VCPU making this request wouldn't have > called kvm_arch_vcpu_put, and its cpu value would still have a value. > > That's why we have the vcpu && vcpu != requester check. > I see, thanks for pointing that out. I'll fix this in the next iteration. Thanks, -- Julien Thierry