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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 B9083C3A5A2 for ; Tue, 3 Sep 2019 16:16:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7DDE32341F for ; Tue, 3 Sep 2019 16:16:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1567527380; bh=osMQ0BnESRREx6z7OgLkTg8p3NdmWL/CptITbHFuliw=; h=Subject:To:Cc:References:From:Date:In-Reply-To:List-ID:From; b=bRgQ8MC3+ijfFxFQYO76LugM4+FyRu6z4HwAlumndymTowsT4ZcGz8s7dU6mnX4W9 Z5Su4ulJRqyN4G3Y4kCkhE6sCnezcxSgLf14JxnqUCXHqtqf6qjYk2J3CPJRzghRDd 2lN+E1HmIqbCvyyeSs55y8fK8jPhl8lCNFcoNWyc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729919AbfICQQT (ORCPT ); Tue, 3 Sep 2019 12:16:19 -0400 Received: from foss.arm.com ([217.140.110.172]:39972 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728571AbfICQQT (ORCPT ); Tue, 3 Sep 2019 12:16:19 -0400 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 ADC9B360; Tue, 3 Sep 2019 09:16:18 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A960A3F246; Tue, 3 Sep 2019 09:16:17 -0700 (PDT) Subject: Re: PCI/kernel msi code vs GIC ITS driver conflict? To: John Garry , Thomas Gleixner , Bjorn Helgaas Cc: Linux PCI , Linuxarm , "luojiaxing@huawei.com" , "linux-kernel@vger.kernel.org" References: From: Marc Zyngier Organization: Approximate Message-ID: <5fd4c1cf-76c1-4054-3754-549317509310@kernel.org> Date: Tue, 3 Sep 2019 17:16:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: 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 Hi John, On 03/09/2019 15:09, John Garry wrote: > Hi Marc, Bjorn, Thomas, > > We've come across a conflict with the kernel/pci msi code and GIC ITS > driver on our arm64 system, whereby we can't unbind and re-bind a PCI > device driver under special conditions. I'll explain... > > Our PCI device support 32 MSIs. The driver attempts to allocate msi > vectors with min msi=17, max msi = 32, and affd.pre vectors = 16. For > our test we make nr_cpus = 1 (just anything less than 16). Just to confirm: this PCI device is requiring Multi-MSI, right? As opposed to MSI-X? > We find that the pci/kernel msi code gives us 17 vectors, but the GIC > ITS code reserves 32 lpi maps in its_irq_domain_alloc(). The problem > then occurs when unbinding the driver in its_irq_domain_free() call, > where we only clear bits for 17 vectors. So if we unbind the driver and > then attempt to bind again, it fails. Is this device, by any chance, sharing its requested-id with another device? By being behind a bridge of some sort? There is some code to deal with it, but I'm not sure it has ever been verified in anger... > Where the fault lies, I can't say. Maybe the kernel msi code should > always give power of 2 vectors - as I understand, the PCI spec mandates > this. Or maybe the GIC ITS driver has a problem in the free path, as > above. Or maybe the PCI driver should not be allowed to request !power > of 2 min/max vectors. > > Opinion? My hunch is that it is an ITS driver bug: the PCI layer is allowed to give any number of MSIs to an endpoint driver, as long as they match the requirements of the allocation for Multi-MSI. That's the responsibility of the ITS driver. If unbind/bind fails, it means that somehow we've missed the freeing of the LPIs, which isn't good. Is the device common enough that I can try and reproduce the issue? If there's a Linux driver somewhere, I can always hack something in emulation and find out... Thanks, M. -- Jazz is not dead, it just smells funny...