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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49C42ECAAD3 for ; Thu, 1 Sep 2022 10:26:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234218AbiIAK00 (ORCPT ); Thu, 1 Sep 2022 06:26:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52712 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234227AbiIAK0D (ORCPT ); Thu, 1 Sep 2022 06:26:03 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id BB2EDC650B; Thu, 1 Sep 2022 03:25:57 -0700 (PDT) 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 EEFC8D6E; Thu, 1 Sep 2022 03:26:02 -0700 (PDT) Received: from [10.57.18.92] (unknown [10.57.18.92]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8D0D83F7B4; Thu, 1 Sep 2022 03:25:54 -0700 (PDT) Message-ID: <3b065fb5-3ca7-8f48-bdf7-daf7604312df@arm.com> Date: Thu, 1 Sep 2022 11:25:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:102.0) Gecko/20100101 Thunderbird/102.2.0 Subject: Re: [PATCH v4 1/2] iommu/s390: Fix race with release_device ops Content-Language: en-GB To: Matthew Rosato , iommu@lists.linux.dev Cc: linux-s390@vger.kernel.org, schnelle@linux.ibm.com, pmorel@linux.ibm.com, borntraeger@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, gerald.schaefer@linux.ibm.com, agordeev@linux.ibm.com, svens@linux.ibm.com, joro@8bytes.org, will@kernel.org, jgg@nvidia.com, linux-kernel@vger.kernel.org References: <20220831201236.77595-1-mjrosato@linux.ibm.com> <20220831201236.77595-2-mjrosato@linux.ibm.com> From: Robin Murphy In-Reply-To: <20220831201236.77595-2-mjrosato@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 2022-08-31 21:12, Matthew Rosato wrote: > With commit fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev > calls") s390-iommu is supposed to handle dynamic switching between IOMMU > domains and the DMA API handling. However, this commit does not > sufficiently handle the case where the device is released via a call > to the release_device op as it may occur at the same time as an opposing > attach_dev or detach_dev since the group mutex is not held over > release_device. This was observed if the device is deconfigured during a > small window during vfio-pci initialization and can result in WARNs and > potential kernel panics. Hmm, the more I think about it, something doesn't sit right about this whole situation... release_device is called via the notifier from device_del() after the device has been removed from its parent bus and largely dismantled; it should definitely not still have a driver bound by that point, so how is VFIO doing things that manage to race at all? Robin. > Handle this by tracking when the device is probed/released via > dev_iommu_priv_set/get(). Ensure that once the device is released only > release_device handles the re-init of the device DMA. > > Fixes: fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev calls") > Signed-off-by: Matthew Rosato > --- > arch/s390/include/asm/pci.h | 1 + > arch/s390/pci/pci.c | 1 + > drivers/iommu/s390-iommu.c | 39 ++++++++++++++++++++++++++++++++++--- > 3 files changed, 38 insertions(+), 3 deletions(-) > > diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h > index 7b4cdadbc023..080251e7b275 100644 > --- a/arch/s390/include/asm/pci.h > +++ b/arch/s390/include/asm/pci.h > @@ -157,6 +157,7 @@ struct zpci_dev { > /* DMA stuff */ > unsigned long *dma_table; > spinlock_t dma_table_lock; > + struct mutex dma_domain_lock; /* protects s390_domain value */ > int tlb_refresh; > > spinlock_t iommu_bitmap_lock; > diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c > index 73cdc5539384..973edd32ecc9 100644 > --- a/arch/s390/pci/pci.c > +++ b/arch/s390/pci/pci.c > @@ -832,6 +832,7 @@ struct zpci_dev *zpci_create_device(u32 fid, u32 fh, enum zpci_state state) > kref_init(&zdev->kref); > mutex_init(&zdev->lock); > mutex_init(&zdev->kzdev_lock); > + mutex_init(&zdev->dma_domain_lock); > > rc = zpci_init_iommu(zdev); > if (rc) > diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c > index c898bcbbce11..1137d669e849 100644 > --- a/drivers/iommu/s390-iommu.c > +++ b/drivers/iommu/s390-iommu.c > @@ -99,6 +99,14 @@ static int s390_iommu_attach_device(struct iommu_domain *domain, > if (!domain_device) > return -ENOMEM; > > + /* Leave now if the device has already been released */ > + mutex_lock(&zdev->dma_domain_lock); > + if (!dev_iommu_priv_get(dev)) { > + mutex_unlock(&zdev->dma_domain_lock); > + kfree(domain_device); > + return 0; > + } > + > if (zdev->dma_table && !zdev->s390_domain) { > cc = zpci_dma_exit_device(zdev); > if (cc) { > @@ -132,9 +140,10 @@ static int s390_iommu_attach_device(struct iommu_domain *domain, > goto out_restore; > } > domain_device->zdev = zdev; > - zdev->s390_domain = s390_domain; > list_add(&domain_device->list, &s390_domain->devices); > spin_unlock_irqrestore(&s390_domain->list_lock, flags); > + zdev->s390_domain = s390_domain; > + mutex_unlock(&zdev->dma_domain_lock); > > return 0; > > @@ -147,6 +156,7 @@ static int s390_iommu_attach_device(struct iommu_domain *domain, > virt_to_phys(zdev->dma_table)); > } > out_free: > + mutex_unlock(&zdev->dma_domain_lock); > kfree(domain_device); > > return rc; > @@ -176,17 +186,22 @@ static void s390_iommu_detach_device(struct iommu_domain *domain, > } > spin_unlock_irqrestore(&s390_domain->list_lock, flags); > > - if (found && (zdev->s390_domain == s390_domain)) { > + mutex_lock(&zdev->dma_domain_lock); > + if (found && (zdev->s390_domain == s390_domain) && > + dev_iommu_priv_get(dev)) { > zdev->s390_domain = NULL; > zpci_unregister_ioat(zdev, 0); > zpci_dma_init_device(zdev); > } > + mutex_unlock(&zdev->dma_domain_lock); > } > > static struct iommu_device *s390_iommu_probe_device(struct device *dev) > { > struct zpci_dev *zdev = to_zpci_dev(dev); > > + dev_iommu_priv_set(dev, zdev); > + > return &zdev->iommu_dev; > } > > @@ -206,10 +221,28 @@ static void s390_iommu_release_device(struct device *dev) > * > * So let's call detach_dev from here if it hasn't been called before. > */ > - if (zdev && zdev->s390_domain) { > + if (zdev) { > + /* > + * Clear priv to block further attaches for this device, > + * ensure detaches don't init DMA. Hold the domain lock > + * to ensure that attach/detach get a consistent view of > + * whether or not the device is released. > + */ > + mutex_lock(&zdev->dma_domain_lock); > + dev_iommu_priv_set(dev, NULL); > + mutex_unlock(&zdev->dma_domain_lock); > + /* Make sure this device is removed from the domain list */ > domain = iommu_get_domain_for_dev(dev); > if (domain) > s390_iommu_detach_device(domain, dev); > + /* Now ensure DMA is initialized from here */ > + mutex_lock(&zdev->dma_domain_lock); > + if (zdev->s390_domain) { > + zdev->s390_domain = NULL; > + zpci_unregister_ioat(zdev, 0); > + zpci_dma_init_device(zdev); > + } > + mutex_unlock(&zdev->dma_domain_lock); > } > } >