From mboxrd@z Thu Jan 1 00:00:00 1970 From: Auger Eric Subject: Re: [PATCH v4 19/22] vfio-pci: Register an iommu fault handler Date: Mon, 25 Feb 2019 18:30:45 +0100 Message-ID: <6e33eab2-2afe-29e5-1c9a-3b8343cdc8ac@redhat.com> References: <20190218135504.25048-1-eric.auger@redhat.com> <20190218135504.25048-20-eric.auger@redhat.com> <20190225142209.GC23257@debian> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190225142209.GC23257@debian> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: =?UTF-8?Q?Vincent_Stehl=c3=a9?= Cc: eric.auger.pro@gmail.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, joro@8bytes.org, alex.williamson@redhat.com, jacob.jun.pan@linux.intel.com, yi.l.liu@linux.intel.com, jean-philippe.brucker@arm.com, will.deacon@arm.com, robin.murphy@arm.com, kevin.tian@intel.com, ashok.raj@intel.com, marc.zyngier@arm.com, christoffer.dall@arm.com, peter.maydell@linaro.org List-Id: iommu@lists.linux-foundation.org Hi Vincent, On 2/25/19 3:22 PM, Vincent Stehlé wrote: > Hi Eric, > > On Mon, Feb 18, 2019 at 02:55:00PM +0100, Eric Auger wrote: >> This patch registers a fault handler which records faults in >> a circular buffer and then signals an eventfd. This buffer is >> exposed within the fault region. >> >> Signed-off-by: Eric Auger >> --- >> drivers/vfio/pci/vfio_pci.c | 49 +++++++++++++++++++++++++++++ >> drivers/vfio/pci/vfio_pci_private.h | 1 + >> 2 files changed, 50 insertions(+) >> >> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c >> index aaf63e5ca2b6..019c9fd380a5 100644 >> --- a/drivers/vfio/pci/vfio_pci.c >> +++ b/drivers/vfio/pci/vfio_pci.c > (..) >> static int vfio_pci_init_fault_region(struct vfio_pci_device *vdev) >> { >> struct vfio_region_fault_prod *header; >> @@ -276,6 +317,13 @@ static int vfio_pci_init_fault_region(struct vfio_pci_device *vdev) >> header = (struct vfio_region_fault_prod *)vdev->fault_pages; >> header->version = -1; >> header->offset = PAGE_SIZE; >> + >> + ret = iommu_register_device_fault_handler(&vdev->pdev->dev, >> + vfio_pci_iommu_dev_fault_handler, >> + vdev); >> + if (ret) >> + goto out; >> + >> return 0; >> out: >> kfree(vdev->fault_pages); > > This patch calls iommu_register_device_fault_handler from > vfio_pci_init_fault_region, leading to the following call stack: > > iommu_register_device_fault_handler > vfio_pci_init_fault_region > vfio_pci_enable > vfio_pci_open > vfio_group_get_device_fd > >> @@ -1420,6 +1468,7 @@ static void vfio_pci_remove(struct pci_dev *pdev) >> vfio_iommu_group_put(pdev->dev.iommu_group, &pdev->dev); >> kfree(vdev->region); >> kfree(vdev->fault_pages); >> + iommu_unregister_device_fault_handler(&pdev->dev); >> mutex_destroy(&vdev->ioeventfds_lock); >> kfree(vdev); > > And then this patch calls iommu_unregister_device_fault_handler from > vfio_pci_remove, and not from vfio_pci_release. Yes you're fully right. Thank you for the time spent debugging the issue. this is a left-over from the previous version and indeed the unregistration should be called from the release ops. By the way, I will package a qemu version for testing this week. Sorry for the delay. Thanks Eric > > I think this means a device cannot be used twice in a row without unloading the > module. > > Here is an example sequence: > > 1. modprobe vfio-pci > 2. Userspace uses VFIO, calls ioctl(VFIO_GROUP_GET_DEVICE_FD) > 2.1. iommu_register_device_fault_handler is called > 3. Userspace exits > 3.1. vfio_pci_release is called, > but iommu_unregister_device_fault_handler is not called > 4. Userspace uses VFIO agin, calls ioctl(VFIO_GROUP_GET_DEVICE_FD) again > 4.1. iommu_register_device_fault_handler is called again, > notices a fault handler is already there, > returns -EBUSY > > Unloading the vfio-pci module will call vfio_pci_remove. > > Maybe iommu_unregister_device_fault_handler should be called from > vfio_pci_release instead of vfio_pci_remove? > > Best regards, > Vincent. >