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=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 C04F7C67839 for ; Fri, 14 Dec 2018 09:37:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F47D20672 for ; Fri, 14 Dec 2018 09:37:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8F47D20672 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 S1729056AbeLNJhD (ORCPT ); Fri, 14 Dec 2018 04:37:03 -0500 Received: from foss.arm.com ([217.140.101.70]:47706 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726418AbeLNJhD (ORCPT ); Fri, 14 Dec 2018 04:37:03 -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 6AF6780D; Fri, 14 Dec 2018 01:37:02 -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 B9AAF3F614; Fri, 14 Dec 2018 01:37:00 -0800 (PST) Subject: Re: [PATCH v2 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: <1543256807-9768-1-git-send-email-julien.thierry@arm.com> <1543256807-9768-2-git-send-email-julien.thierry@arm.com> <20181211102015.GV30263@e113682-lin.lund.arm.com> From: Julien Thierry Message-ID: <0573c8b2-db76-19e3-db76-5433b2e4ad0a@arm.com> Date: Fri, 14 Dec 2018 09:36:59 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181211102015.GV30263@e113682-lin.lund.arm.com> Content-Type: text/plain; charset=utf-8 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 11/12/2018 10:20, Christoffer Dall wrote: > On Mon, Nov 26, 2018 at 06:26:44PM +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 we cannot reschedule a vcpu. >> >> Solve this by waiting for all vcpus to be halted after emmiting the halt >> request. >> >> 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 | 36 ++++++++++++++---------------------- >> 1 file changed, 14 insertions(+), 22 deletions(-) >> >> diff --git a/virt/kvm/arm/vgic/vgic-mmio.c b/virt/kvm/arm/vgic/vgic-mmio.c >> index f56ff1c..5c76a92 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 +347,21 @@ 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) { >> + if (tmp == vcpu) >> + continue; >> + >> + while (tmp->cpu != -1) >> + cond_resched(); >> + } > > I'm actually thinking we don't need this loop at all after the requet > rework which causes: > > 1. kvm_arm_halt_guest() to use kvm_make_all_cpus_request(kvm, KVM_REQ_SLEEP), and > 2. KVM_REQ_SLEEP uses REQ_WAIT, and > 3. REQ_WAIT requires the VCPU to respond to IPIs before returning, and > 4. a VCPU thread can only respond when it enables interrupt, and > 5. enabling interrupts when running a VCPU only happens after syncing > the VGIC hwstate. > > Does that make sense? I'm not super familiar with what goes on with the vgic hwstate syncing, but looking at kvm_arm_halt_guest() and kvm_arch_vcpu_ioctl_run(), I agree with the reasoning. > It would be good if someone can validate this, but if it holds this > patch just becomes a nice deletion of the logic in > vgic-mmio_change_active. > As long as running kvm_vgic_sync_hwstate() on each vcpu is all that is needed before we can modify the active state, I think your solution is definitely the way to go. Thanks, -- Julien Thierry