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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 317E5C3A589 for ; Thu, 15 Aug 2019 14:58:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E43D20656 for ; Thu, 15 Aug 2019 14:58:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732544AbfHOO6d (ORCPT ); Thu, 15 Aug 2019 10:58:33 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:39964 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728500AbfHOO6d (ORCPT ); Thu, 15 Aug 2019 10:58:33 -0400 Received: from pd9ef1cb8.dip0.t-ipconnect.de ([217.239.28.184] helo=nanos.glx-home) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hyHCu-0007SL-HD; Thu, 15 Aug 2019 16:58:28 +0200 Date: Thu, 15 Aug 2019 16:58:27 +0200 (CEST) From: Thomas Gleixner To: Ben Luo cc: alex.williamson@redhat.com, linux-kernel@vger.kernel.org, tao.ma@linux.alibaba.com, gerry@linux.alibaba.com, nanhai.zou@linux.alibaba.com, linyunsheng@huawei.com Subject: Re: [PATCH v3 2/3] genirq: introduce update_irq_devid() In-Reply-To: <6343a7e34ffdd0ddcd730996fc5dad3024e42251.1565857737.git.luoben@linux.alibaba.com> Message-ID: References: <6343a7e34ffdd0ddcd730996fc5dad3024e42251.1565857737.git.luoben@linux.alibaba.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ben, On Thu, 15 Aug 2019, Ben Luo wrote: > Sometimes, only the dev_id field of irqaction need to be changed. > E.g. KVM VM with device passthru via VFIO may switch irq injection > path between KVM irqfd and userspace eventfd. These two paths > share the same irq num and handler for the same vector of a device, s/irq num/interrupt number/ Changelogs are text and should not contain cryptic abbreviations. > only with different dev_id referencing to different fds' contexts. > > So, instead of free/request irq, only update dev_id of irqaction. Please write functions like this: function_name() so they can be easily identified in the text as such. > This narrows the gap for setting up new irq (and irte, if has) What does that mean: "narrows the gap" What's the gap and why is it only made smaller and not closed? > and also gains some performance benefit. > > Signed-off-by: Ben Luo > Reviewed-by: Liu Jiang I prefer to see the 'reviewed-by' as a reply on LKML rather than coming from some internal process. > Reviewed-by: Thomas Gleixner While I reviewed the previous version, I surely did not give a 'Reviewed-by' tag. That tag means that the person did review the patch and did not find an issue. I surely found issues, right? > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c > index 6f9b20f..a76ef61 100644 > --- a/kernel/irq/manage.c > +++ b/kernel/irq/manage.c > @@ -2064,6 +2064,84 @@ int request_threaded_irq(unsigned int irq, irq_handler_t handler, > EXPORT_SYMBOL(request_threaded_irq); > > /** > + * update_irq_devid - update irq dev_id to a new one Can you please name this: irq_update_devid(). We try to have a consistent name space for new functions. > + * @irq: Interrupt line to update > + * @dev_id: A cookie to find the irqaction to update > + * @new_dev_id: New cookie passed to the handler function Can you please arrange these in tabular fashion: * @irq: Interrupt line to update * @dev_id: A cookie to find the irqaction to update * @new_dev_id: New cookie passed to the handler function > + * Sometimes, only the cookie data need to be changed. > + * Instead of free/request irq, only update dev_id here > + * Not only to gain some performance benefit, but also > + * reduce the risk of losing interrupt. > + * > + * E.g. irq affinity setting in a VM with VFIO passthru Again. Please write it out 'interrupt' and everything else. > + * device is carried out in a free-then-request-irq way > + * since lack of this very function. The free_irq() That does not make sense. The function is there for such a use case. So immediately when the VFIO change is merged this comment is stale and bogus. > + * eventually triggers deactivation of IR domain, which > + * will cleanup IRTE. There is a gap before request_irq() > + * finally setup the IRTE again. In this gap, a in-flight > + * irq buffering in hardware layer may trigger DMAR fault > + * and be lost. Exactly this information wants to be in the changelog. > + * > + * On failure, it returns a negative value. On success, > + * it returns 0 > + */ > +int update_irq_devid(unsigned int irq, void *dev_id, void *new_dev_id) > +{ > + struct irq_desc *desc = irq_to_desc(irq); > + struct irqaction *action, **action_ptr; > + unsigned long flags; > + > + if (in_interrupt()) { > + WARN(1, "Trying to update IRQ %d (dev_id %p to %p) from IRQ context!\n", > + irq, dev_id, new_dev_id); > + return -EPERM; > + } if (WARN(....) > + > + if (!desc) > + return -EINVAL; > + > + chip_bus_lock(desc); This does not need to take bus lock. The action pointer is sufficiently protected by desc->lock. > + raw_spin_lock_irqsave(&desc->lock, flags); > + > + /* > + * There can be multiple actions per IRQ descriptor, find the right > + * one based on the dev_id: > + */ > + action_ptr = &desc->action; > + for (;;) { > + action = *action_ptr; > + > + if (!action) { > + raw_spin_unlock_irqrestore(&desc->lock, flags); > + chip_bus_sync_unlock(desc); > + WARN(1, "Trying to update already-free IRQ %d (dev_id %p to %p)\n", > + irq, dev_id, new_dev_id); > + return -ENXIO; > + } > + > + if (action->dev_id == dev_id) { > + action->dev_id = new_dev_id; > + break; > + } > + action_ptr = &action->next; > + } > + > + raw_spin_unlock_irqrestore(&desc->lock, flags); > + chip_bus_sync_unlock(desc); > + > + /* > + * Make sure it's not being used on another CPU: > + * There is a risk of UAF for old *dev_id, if it is > + * freed in a short time after this func returns function please. Also it does not matter whether the time is short or not. The point is: Ensure that an interrupt in flight on another CPU which uses the old 'dev_id' has completed because the caller can free the memory to which it points after this function returns. But this has another twist: CPU0 CPU1 interrupt primary_handler(old_dev_id) do_stuff_on(old_dev_id) return WAKE_THREAD; update_dev_id() wakeup_thread(); action->dev_id = new_dev_id; irq_thread() secondary_handler(new_dev_id) That's broken and synchronize_irq() does not protect against it. > + */ > + synchronize_irq(irq); Thanks, tglx