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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 D8F51C433E0 for ; Tue, 30 Jun 2020 16:33:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AE5FB20722 for ; Tue, 30 Jun 2020 16:33:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593534816; bh=TmHz8DGHOqml0apr+BZwB0ErlFOXBuxedj6hFvuKkWU=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=ZmVUMvgHrJcD6+6Pfugca/0JO1rEmFngzURFujS7pevhzseaWmIrGulOCleVSZDtD Y5fEAM1i3VMIwjhaEWJlWjRLtS+GcwdeRHyklyhUIOeLcJDb9c6LVXTWWG2HrseZfg v3pcft4peIKPYRjfudSr27P7ExBDGXJ+sjVVS/j4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728340AbgF3Qdg (ORCPT ); Tue, 30 Jun 2020 12:33:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:47714 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726639AbgF3Qdf (ORCPT ); Tue, 30 Jun 2020 12:33:35 -0400 Received: from localhost (mobile-166-175-191-139.mycingular.net [166.175.191.139]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1E2C4206BE; Tue, 30 Jun 2020 16:33:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593534814; bh=TmHz8DGHOqml0apr+BZwB0ErlFOXBuxedj6hFvuKkWU=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=zR0G0CcrzfpbGAxDdTupdXd6nQt0O1m8OD4+l/bda25b+lumO9y1UgcgAEyqpxxWo Ij0iyCyCH55OP2HE+3vGntR5fPEYXpVqqxQb9rPkSkTRuIE7K4CzKXGLT4lJdWTDbt VAs0nxZO8QvhCCn1fQU+hc6rcEgMA0gMTwRYHQ98= Date: Tue, 30 Jun 2020 11:33:32 -0500 From: Bjorn Helgaas To: Andy Shevchenko , Thomas Gleixner Cc: Jon Derrick , Lorenzo Pieralisi , linux-pci@vger.kernel.org, Sushma Kalakota Subject: Re: [PATCH] PCI: vmd: Keep fwnode allocated through VMD irqdomain life Message-ID: <20200630163332.GA3437879@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200630093908.GP3703480@smile.fi.intel.com> Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Tue, Jun 30, 2020 at 12:39:08PM +0300, Andy Shevchenko wrote: > On Mon, Jun 29, 2020 at 06:20:11PM -0500, Bjorn Helgaas wrote: > > On Thu, Jun 25, 2020 at 02:58:23PM -0500, Bjorn Helgaas wrote: > > > [+cc Thomas] > > > > > > On Thu, Jun 25, 2020 at 12:24:49PM -0400, Jon Derrick wrote: > > > > From: Andy Shevchenko > > > > > > > > The VMD domain does not subscribe to ACPI, and so does not operate on > > > > it's irqdomain fwnode. It was freeing the handle after allocation of the > > > > domain. As of 181e9d4efaf6a (irqdomain: Make __irq_domain_add() less > > > > OF-dependent), the fwnode is put during irq_domain_remove causing a page > > > > fault. This patch keeps VMD's fwnode allocated through the lifetime of > > > > the VMD irqdomain. > > > > > > > > Fixes: ae904cafd59d ("PCI/vmd: Create named irq domain") > > > > Signed-off-by: Andy Shevchenko > > > > Co-developed-by: Andy Shevchenko > > > > Signed-off-by: Jon Derrick > > > > --- > > > > Hi Lorenzo, Bjorn, > > > > > > > > Please take this patch for v5.8 fixes. It fixes an issue during VMD > > > > unload. > > > > > > I tentatively applied this to for-linus for v5.8. > > > > > > But I would like to clarify the commit log. It says this fixes > > > Thomas' ae904cafd59d ("PCI/vmd: Create named irq domain"). That > > > appeared in v4.13, which suggests that this patch should be backported > > > to v4.13 and later. > > > > I didn't word this correctly. What I meant was "I will consider > > applying this after the commit log is clarified." Just FYI that this > > isn't resolved yet. > > > > Since this is proposed for v5.8, I really want to understand this > > better before asking Linus to pull it as a fix. > > The problem here is in the original patch which relies on the > knowledge that fwnode is (was) not used anyhow specifically for ACPI > case. That said, it makes fwnode a dangling pointer which I > personally consider as a mine left for others. That's why the Fixes > refers to the initial commit. The latter just has been blasted on > that mine. IIUC, you're saying this pattern: fwnode = irq_domain_alloc_named_id_fwnode(...) irq_domain = pci_msi_create_irq_domain(fwnode, ...) irq_domain_free_fwnode(fwnode) leaves a dangling fwnode pointer. That does look suspicious because __irq_domain_add() saves fwnode: irq_domain = pci_msi_create_irq_domain(fwnode, ...) msi_create_irq_domain(fwnode, ...) irq_domain_create_hierarchy(..., fwnode, ...) irq_domain_create_linear(fwnode, ...) __irq_domain_add(fwnode, ...) domain->fwnode = fwnode and irq_domain_free_fwnode() frees it. But I'm confused because there are several other instances of this pattern: bridge_probe() # arch/mips/pci/pci-xtalk-bridge.c mp_irqdomain_create() arch_init_msi_domain() arch_create_remap_msi_irq_domain() dmar_get_irq_domain() hpet_create_irq_domain() ... Are they all wrong? I definitely think it's a bad idea to keep a copy of a pointer after we free the data it points to. But if they're all wrong, I don't want to fix just one and leave all the others. Thomas, can you enlighten us? > If you think that's fine to have such trick, feel free to update Fixes tag. > > > > But it's not clear to me that ae904cafd59d is actually broken, since > > > the log also says the problem appeared after 181e9d4efaf6 ("irqdomain: > > > Make __irq_domain_add() less OF-dependent"), which we just merged for > > > v5.8-rc1. > > > > > > And obviously, freeing the fwnode doesn't *cause* a page fault. A > > > use-after-free might cause a fault, but it's not clear where that > > > happens. I guess fwnode is used in the interval between: > > > > > > vmd_enable_domain > > > pci_msi_create_irq_domain > > > > > > ... <-- fwnode used here somewhere > > > > > > vmd_remove > > > vmd_cleanup_srcu > > > irq_domain_free_fwnode > > > > > > But I can't tell how 181e9d4efaf6a and/or ae904cafd59d are related to > > > that. > > > > > > > drivers/pci/controller/vmd.c | 8 ++++++-- > > > > 1 file changed, 6 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c > > > > index e386d4eac407..ebec0a6e77ed 100644 > > > > --- a/drivers/pci/controller/vmd.c > > > > +++ b/drivers/pci/controller/vmd.c > > > > @@ -546,9 +546,10 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features) > > > > > > > > vmd->irq_domain = pci_msi_create_irq_domain(fn, &vmd_msi_domain_info, > > > > x86_vector_domain); > > > > - irq_domain_free_fwnode(fn); > > > > - if (!vmd->irq_domain) > > > > + if (!vmd->irq_domain) { > > > > + irq_domain_free_fwnode(fn); > > > > return -ENODEV; > > > > + } > > > > > > > > pci_add_resource(&resources, &vmd->resources[0]); > > > > pci_add_resource_offset(&resources, &vmd->resources[1], offset[0]); > > > > @@ -559,6 +560,7 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features) > > > > if (!vmd->bus) { > > > > pci_free_resource_list(&resources); > > > > irq_domain_remove(vmd->irq_domain); > > > > + irq_domain_free_fwnode(fn); > > > > return -ENODEV; > > > > } > > > > > > > > @@ -672,6 +674,7 @@ static void vmd_cleanup_srcu(struct vmd_dev *vmd) > > > > static void vmd_remove(struct pci_dev *dev) > > > > { > > > > struct vmd_dev *vmd = pci_get_drvdata(dev); > > > > + struct fwnode_handle *fn = vmd->irq_domain->fwnode; > > > > > > > > sysfs_remove_link(&vmd->dev->dev.kobj, "domain"); > > > > pci_stop_root_bus(vmd->bus); > > > > @@ -679,6 +682,7 @@ static void vmd_remove(struct pci_dev *dev) > > > > vmd_cleanup_srcu(vmd); > > > > vmd_detach_resources(vmd); > > > > irq_domain_remove(vmd->irq_domain); > > > > + irq_domain_free_fwnode(fn); > > > > } > > > > > > > > #ifdef CONFIG_PM_SLEEP > > > > -- > > > > 2.18.1 > > > > > > -- > With Best Regards, > Andy Shevchenko > >