From: Alex Williamson <alex.williamson@redhat.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: cohuck@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, peterx@redhat.com
Subject: Re: [PATCH v1 07/14] vfio: Add a device notifier interface
Date: Tue, 9 Mar 2021 08:45:13 -0700 [thread overview]
Message-ID: <20210309084513.51fd2a97@x1.home.shazbot.org> (raw)
In-Reply-To: <20210309004627.GD4247@nvidia.com>
On Mon, 8 Mar 2021 20:46:27 -0400
Jason Gunthorpe <jgg@nvidia.com> wrote:
> On Mon, Mar 08, 2021 at 02:48:30PM -0700, Alex Williamson wrote:
> > Using a vfio device, a notifier block can be registered to receive
> > select device events. Notifiers can only be registered for contained
> > devices, ie. they are available through a user context. Registration
> > of a notifier increments the reference to that container context
> > therefore notifiers must minimally respond to the release event by
> > asynchronously removing notifiers.
> >
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > drivers/vfio/Kconfig | 1 +
> > drivers/vfio/vfio.c | 35 +++++++++++++++++++++++++++++++++++
> > include/linux/vfio.h | 9 +++++++++
> > 3 files changed, 45 insertions(+)
> >
> > diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
> > index 90c0525b1e0c..9a67675c9b6c 100644
> > +++ b/drivers/vfio/Kconfig
> > @@ -23,6 +23,7 @@ menuconfig VFIO
> > tristate "VFIO Non-Privileged userspace driver framework"
> > select IOMMU_API
> > select VFIO_IOMMU_TYPE1 if (X86 || S390 || ARM || ARM64)
> > + select SRCU
> > help
> > VFIO provides a framework for secure userspace device drivers.
> > See Documentation/driver-api/vfio.rst for more details.
> > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> > index c47895539a1a..7f6d00e54e83 100644
> > +++ b/drivers/vfio/vfio.c
> > @@ -105,6 +105,7 @@ struct vfio_device {
> > struct list_head group_next;
> > void *device_data;
> > struct inode *inode;
> > + struct srcu_notifier_head notifier;
> > };
> >
> > #ifdef CONFIG_VFIO_NOIOMMU
> > @@ -601,6 +602,7 @@ struct vfio_device *vfio_group_create_device(struct vfio_group *group,
> > device->ops = ops;
> > device->device_data = device_data;
> > dev_set_drvdata(dev, device);
> > + srcu_init_notifier_head(&device->notifier);
> >
> > /* No need to get group_lock, caller has group reference */
> > vfio_group_get(group);
> > @@ -1785,6 +1787,39 @@ static const struct file_operations vfio_device_fops = {
> > .mmap = vfio_device_fops_mmap,
> > };
> >
> > +int vfio_device_register_notifier(struct vfio_device *device,
> > + struct notifier_block *nb)
> > +{
> > + int ret;
> > +
> > + /* Container ref persists until unregister on success */
> > + ret = vfio_group_add_container_user(device->group);
>
> I'm having trouble guessing why we need to refcount the group to add a
> notifier to the device's notifier chain?
>
> I suppose it actually has to do with the MMIO mapping? But I don't
> know what the relation is between MMIO mappings in the IOMMU and the
> container? This could deserve a comment?
Sure, I can add a comment. We want to make sure the device remains
within an IOMMU context so long as we have a DMA mapping to the device
MMIO, which could potentially manipulate the device. IOMMU context is
managed a the group level.
> > +void vfio_device_unregister_notifier(struct vfio_device *device,
> > + struct notifier_block *nb)
> > +{
> > + if (!srcu_notifier_chain_unregister(&device->notifier, nb))
> > + vfio_group_try_dissolve_container(device->group);
> > +}
> > +EXPORT_SYMBOL_GPL(vfio_device_unregister_notifier);
>
> Is the SRCU still needed with the new locking? With a cursory look I
> only noticed this called under the reflck->lock ?
When registering the notifier, the iommu->lock is held. During the
callback, the same lock is acquired, so we'd have AB-BA otherwise.
Thanks,
Alex
next prev parent reply other threads:[~2021-03-09 15:45 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 21:47 [PATCH v1 00/14] vfio: Device memory DMA mapping improvements Alex Williamson
2021-03-08 21:47 ` [PATCH v1 01/14] vfio: Create vfio_fs_type with inode per device Alex Williamson
2021-03-09 8:36 ` Christoph Hellwig
2021-04-09 4:54 ` 答复: " Zengtao (B)
2021-04-09 14:24 ` Alex Williamson
2021-04-09 17:32 ` Jason Gunthorpe
2021-04-12 4:03 ` 答复: " Zengtao (B)
2021-04-12 4:09 ` Zengtao (B)
2021-03-08 21:47 ` [PATCH v1 02/14] vfio: Update vfio_add_group_dev() API Alex Williamson
2021-03-10 7:48 ` Christoph Hellwig
2021-03-10 12:19 ` Jason Gunthorpe
2021-03-10 15:28 ` Alex Williamson
2021-03-11 11:23 ` Christoph Hellwig
2021-03-08 21:47 ` [PATCH v1 03/14] vfio: Export unmap_mapping_range() wrapper Alex Williamson
2021-03-08 21:48 ` [PATCH v1 04/14] vfio/pci: Use vfio_device_unmap_mapping_range() Alex Williamson
2021-03-08 21:48 ` [PATCH v1 05/14] vfio: Create a vfio_device from vma lookup Alex Williamson
2021-03-08 21:48 ` [PATCH v1 06/14] vfio: Add vma to pfn callback Alex Williamson
2021-03-09 0:33 ` Jason Gunthorpe
2021-03-08 21:48 ` [PATCH v1 07/14] vfio: Add a device notifier interface Alex Williamson
2021-03-09 0:46 ` Jason Gunthorpe
2021-03-09 15:45 ` Alex Williamson [this message]
2021-03-09 16:47 ` Jason Gunthorpe
2021-03-10 7:56 ` Christoph Hellwig
2021-03-19 22:25 ` Alex Williamson
2021-03-22 15:16 ` Christoph Hellwig
2021-03-08 21:48 ` [PATCH v1 08/14] vfio/pci: Notify on device release Alex Williamson
2021-03-08 21:48 ` [PATCH v1 09/14] vfio/type1: Refactor pfn_list clearing Alex Williamson
2021-03-10 8:01 ` Christoph Hellwig
2021-03-08 21:49 ` [PATCH v1 10/14] vfio/type1: Pass iommu and dma objects through to vaddr_get_pfn Alex Williamson
2021-03-08 21:49 ` [PATCH v1 11/14] vfio/type1: Register device notifier Alex Williamson
2021-03-10 8:03 ` Christoph Hellwig
2021-03-08 21:49 ` [PATCH v1 12/14] vfio/type1: Support batching of device mappings Alex Williamson
2021-03-09 1:04 ` Jason Gunthorpe
2021-03-08 21:49 ` [PATCH v1 13/14] vfio: Remove extern from declarations across vfio Alex Williamson
2021-03-09 0:21 ` Halil Pasic
2021-03-09 1:07 ` Jason Gunthorpe
2021-03-08 21:49 ` [PATCH v1 14/14] vfio: Cleanup use of bare unsigned Alex Williamson
2021-03-09 1:07 ` Jason Gunthorpe
2021-03-09 8:31 ` Christoph Hellwig
2021-03-09 1:06 ` [PATCH v1 00/14] vfio: Device memory DMA mapping improvements Jason Gunthorpe
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