Re: [Intel-gfx] [PATCH v3 0/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

Re: [Intel-gfx] [PATCH v3 0/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Alex Williamson]

On Thu, 19 May 2022 14:33:10 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> As discussed in this thread:
> 
> https://lore.kernel.org/kvm/20220516172734.GE1343366@nvidia.com/
> 
> Let's remove VFIO_GROUP_NOTIFY_SET_KVM and instead assume the association
> has already been established prior to device_open.  For the types today
> that need a KVM (GVT, vfio-ap) these will fail if a KVM is not found.
> Looking ahead, vfio-pci-zdev will optionally want the KVM association
> (enable hardware assists) but it will not be a hard requirement (still
> want to allow other, non-KVM userspace usage). 
> 
> This is built on top of vfio-next and tested with s390x-pci
> (zdev-kvm series) and vfio-ap (GVT changes are compile-tested only)
> 
> Changes for v3:
> - merge branches under if (device->open_count == 1) (Kevin)
> - move device->open_count-- out from group_rwsem (Kevin)
> - drop null KVM check (Christoph)
> - remove extra kvm_{get,put}_kvm from vfio_ap_ops, it was already getting
>   a reference (Jason)
> - Add comment about kvm reference in vfio.h (Jason)
> - Return -EINVAL if !kvm for vfio-ap (Tony)
> 
> Changes for v2:
> - gvt no longer needs release_work, get rid of it (Christoph)
> - a few compile fixes for gvt
> - update commit to mention fixes gvt oops (Jason)
> - s/down_write/down_read/ in a few spots (Jason)
> - avoid kvm build dependency by holding group read lock over device
>   open/close and put the onus on the driver to obtain a reference if
>   it will actually use the kvm pointer.  Document the requirement,
>   use lockdep_assert to ensure lock is held during register_notifer;
>   today all callers are from driver open_device. 
> 
> Matthew Rosato (1):
>   vfio: remove VFIO_GROUP_NOTIFY_SET_KVM
> 
>  drivers/gpu/drm/i915/gvt/gtt.c        |  4 +-
>  drivers/gpu/drm/i915/gvt/gvt.h        |  3 -
>  drivers/gpu/drm/i915/gvt/kvmgt.c      | 82 ++++++--------------------
>  drivers/s390/crypto/vfio_ap_ops.c     | 35 ++---------
>  drivers/s390/crypto/vfio_ap_private.h |  3 -
>  drivers/vfio/vfio.c                   | 83 ++++++++++-----------------
>  include/linux/vfio.h                  |  6 +-
>  7 files changed, 57 insertions(+), 159 deletions(-)

Applied to vfio next branch for v5.19.  Thanks,

Alex

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Jason Gunthorpe]

On Thu, May 19, 2022 at 02:33:11PM -0400, Matthew Rosato wrote:
> Rather than relying on a notifier for associating the KVM with
> the group, let's assume that the association has already been
> made prior to device_open.  The first time a device is opened
> associate the group KVM with the device.
> 
> This fixes a user-triggerable oops in GVT.
> 
> Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
>  drivers/gpu/drm/i915/gvt/gtt.c        |  4 +-
>  drivers/gpu/drm/i915/gvt/gvt.h        |  3 -
>  drivers/gpu/drm/i915/gvt/kvmgt.c      | 82 ++++++--------------------
>  drivers/s390/crypto/vfio_ap_ops.c     | 35 ++---------
>  drivers/s390/crypto/vfio_ap_private.h |  3 -
>  drivers/vfio/vfio.c                   | 83 ++++++++++-----------------
>  include/linux/vfio.h                  |  6 +-
>  7 files changed, 57 insertions(+), 159 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Alex Williamson]

Hi Zhi & Zhenyu,

Please review gvt changes below, I'd prefer to get your ack included.
Thanks!

Alex

On Thu, 19 May 2022 14:33:11 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> Rather than relying on a notifier for associating the KVM with
> the group, let's assume that the association has already been
> made prior to device_open.  The first time a device is opened
> associate the group KVM with the device.
> 
> This fixes a user-triggerable oops in GVT.
> 
> Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
>  drivers/gpu/drm/i915/gvt/gtt.c        |  4 +-
>  drivers/gpu/drm/i915/gvt/gvt.h        |  3 -
>  drivers/gpu/drm/i915/gvt/kvmgt.c      | 82 ++++++--------------------
>  drivers/s390/crypto/vfio_ap_ops.c     | 35 ++---------
>  drivers/s390/crypto/vfio_ap_private.h |  3 -
>  drivers/vfio/vfio.c                   | 83 ++++++++++-----------------
>  include/linux/vfio.h                  |  6 +-
>  7 files changed, 57 insertions(+), 159 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index 9c5cc2800975..b4f69364f9a1 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -51,7 +51,7 @@ static int preallocated_oos_pages = 8192;
>  
>  static bool intel_gvt_is_valid_gfn(struct intel_vgpu *vgpu, unsigned long gfn)
>  {
> -	struct kvm *kvm = vgpu->kvm;
> +	struct kvm *kvm = vgpu->vfio_device.kvm;
>  	int idx;
>  	bool ret;
>  
> @@ -1185,7 +1185,7 @@ static int is_2MB_gtt_possible(struct intel_vgpu *vgpu,
>  
>  	if (!vgpu->attached)
>  		return -EINVAL;
> -	pfn = gfn_to_pfn(vgpu->kvm, ops->get_pfn(entry));
> +	pfn = gfn_to_pfn(vgpu->vfio_device.kvm, ops->get_pfn(entry));
>  	if (is_error_noslot_pfn(pfn))
>  		return -EINVAL;
>  	return PageTransHuge(pfn_to_page(pfn));
> diff --git a/drivers/gpu/drm/i915/gvt/gvt.h b/drivers/gpu/drm/i915/gvt/gvt.h
> index 2af4c83e733c..aee1a45da74b 100644
> --- a/drivers/gpu/drm/i915/gvt/gvt.h
> +++ b/drivers/gpu/drm/i915/gvt/gvt.h
> @@ -227,9 +227,6 @@ struct intel_vgpu {
>  	struct mutex cache_lock;
>  
>  	struct notifier_block iommu_notifier;
> -	struct notifier_block group_notifier;
> -	struct kvm *kvm;
> -	struct work_struct release_work;
>  	atomic_t released;
>  
>  	struct kvm_page_track_notifier_node track_node;
> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
> index 7655ffa97d51..e2f6c56ab342 100644
> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
> @@ -228,8 +228,6 @@ static void intel_gvt_cleanup_vgpu_type_groups(struct intel_gvt *gvt)
>  	}
>  }
>  
> -static void intel_vgpu_release_work(struct work_struct *work);
> -
>  static void gvt_unpin_guest_page(struct intel_vgpu *vgpu, unsigned long gfn,
>  		unsigned long size)
>  {
> @@ -761,23 +759,6 @@ static int intel_vgpu_iommu_notifier(struct notifier_block *nb,
>  	return NOTIFY_OK;
>  }
>  
> -static int intel_vgpu_group_notifier(struct notifier_block *nb,
> -				     unsigned long action, void *data)
> -{
> -	struct intel_vgpu *vgpu =
> -		container_of(nb, struct intel_vgpu, group_notifier);
> -
> -	/* the only action we care about */
> -	if (action == VFIO_GROUP_NOTIFY_SET_KVM) {
> -		vgpu->kvm = data;
> -
> -		if (!data)
> -			schedule_work(&vgpu->release_work);
> -	}
> -
> -	return NOTIFY_OK;
> -}
> -
>  static bool __kvmgt_vgpu_exist(struct intel_vgpu *vgpu)
>  {
>  	struct intel_vgpu *itr;
> @@ -789,7 +770,7 @@ static bool __kvmgt_vgpu_exist(struct intel_vgpu *vgpu)
>  		if (!itr->attached)
>  			continue;
>  
> -		if (vgpu->kvm == itr->kvm) {
> +		if (vgpu->vfio_device.kvm == itr->vfio_device.kvm) {
>  			ret = true;
>  			goto out;
>  		}
> @@ -806,7 +787,6 @@ static int intel_vgpu_open_device(struct vfio_device *vfio_dev)
>  	int ret;
>  
>  	vgpu->iommu_notifier.notifier_call = intel_vgpu_iommu_notifier;
> -	vgpu->group_notifier.notifier_call = intel_vgpu_group_notifier;
>  
>  	events = VFIO_IOMMU_NOTIFY_DMA_UNMAP;
>  	ret = vfio_register_notifier(vfio_dev, VFIO_IOMMU_NOTIFY, &events,
> @@ -817,38 +797,32 @@ static int intel_vgpu_open_device(struct vfio_device *vfio_dev)
>  		goto out;
>  	}
>  
> -	events = VFIO_GROUP_NOTIFY_SET_KVM;
> -	ret = vfio_register_notifier(vfio_dev, VFIO_GROUP_NOTIFY, &events,
> -				     &vgpu->group_notifier);
> -	if (ret != 0) {
> -		gvt_vgpu_err("vfio_register_notifier for group failed: %d\n",
> -			ret);
> -		goto undo_iommu;
> -	}
> -
>  	ret = -EEXIST;
>  	if (vgpu->attached)
> -		goto undo_register;
> +		goto undo_iommu;
>  
>  	ret = -ESRCH;
> -	if (!vgpu->kvm || vgpu->kvm->mm != current->mm) {
> +	if (!vgpu->vfio_device.kvm ||
> +	    vgpu->vfio_device.kvm->mm != current->mm) {
>  		gvt_vgpu_err("KVM is required to use Intel vGPU\n");
> -		goto undo_register;
> +		goto undo_iommu;
>  	}
>  
> +	kvm_get_kvm(vgpu->vfio_device.kvm);
> +
>  	ret = -EEXIST;
>  	if (__kvmgt_vgpu_exist(vgpu))
> -		goto undo_register;
> +		goto undo_iommu;
>  
>  	vgpu->attached = true;
> -	kvm_get_kvm(vgpu->kvm);
>  
>  	kvmgt_protect_table_init(vgpu);
>  	gvt_cache_init(vgpu);
>  
>  	vgpu->track_node.track_write = kvmgt_page_track_write;
>  	vgpu->track_node.track_flush_slot = kvmgt_page_track_flush_slot;
> -	kvm_page_track_register_notifier(vgpu->kvm, &vgpu->track_node);
> +	kvm_page_track_register_notifier(vgpu->vfio_device.kvm,
> +					 &vgpu->track_node);
>  
>  	debugfs_create_ulong(KVMGT_DEBUGFS_FILENAME, 0444, vgpu->debugfs,
>  			     &vgpu->nr_cache_entries);
> @@ -858,10 +832,6 @@ static int intel_vgpu_open_device(struct vfio_device *vfio_dev)
>  	atomic_set(&vgpu->released, 0);
>  	return 0;
>  
> -undo_register:
> -	vfio_unregister_notifier(vfio_dev, VFIO_GROUP_NOTIFY,
> -				 &vgpu->group_notifier);
> -
>  undo_iommu:
>  	vfio_unregister_notifier(vfio_dev, VFIO_IOMMU_NOTIFY,
>  				 &vgpu->iommu_notifier);
> @@ -880,8 +850,9 @@ static void intel_vgpu_release_msi_eventfd_ctx(struct intel_vgpu *vgpu)
>  	}
>  }
>  
> -static void __intel_vgpu_release(struct intel_vgpu *vgpu)
> +static void intel_vgpu_close_device(struct vfio_device *vfio_dev)
>  {
> +	struct intel_vgpu *vgpu = vfio_dev_to_vgpu(vfio_dev);
>  	struct drm_i915_private *i915 = vgpu->gvt->gt->i915;
>  	int ret;
>  
> @@ -898,35 +869,19 @@ static void __intel_vgpu_release(struct intel_vgpu *vgpu)
>  	drm_WARN(&i915->drm, ret,
>  		 "vfio_unregister_notifier for iommu failed: %d\n", ret);
>  
> -	ret = vfio_unregister_notifier(&vgpu->vfio_device, VFIO_GROUP_NOTIFY,
> -				       &vgpu->group_notifier);
> -	drm_WARN(&i915->drm, ret,
> -		 "vfio_unregister_notifier for group failed: %d\n", ret);
> -
>  	debugfs_remove(debugfs_lookup(KVMGT_DEBUGFS_FILENAME, vgpu->debugfs));
>  
> -	kvm_page_track_unregister_notifier(vgpu->kvm, &vgpu->track_node);
> -	kvm_put_kvm(vgpu->kvm);
> +	kvm_page_track_unregister_notifier(vgpu->vfio_device.kvm,
> +					   &vgpu->track_node);
>  	kvmgt_protect_table_destroy(vgpu);
>  	gvt_cache_destroy(vgpu);
>  
>  	intel_vgpu_release_msi_eventfd_ctx(vgpu);
>  
> -	vgpu->kvm = NULL;
>  	vgpu->attached = false;
> -}
> -
> -static void intel_vgpu_close_device(struct vfio_device *vfio_dev)
> -{
> -	__intel_vgpu_release(vfio_dev_to_vgpu(vfio_dev));
> -}
> -
> -static void intel_vgpu_release_work(struct work_struct *work)
> -{
> -	struct intel_vgpu *vgpu =
> -		container_of(work, struct intel_vgpu, release_work);
>  
> -	__intel_vgpu_release(vgpu);
> +	if (vgpu->vfio_device.kvm)
> +		kvm_put_kvm(vgpu->vfio_device.kvm);
>  }
>  
>  static u64 intel_vgpu_get_bar_addr(struct intel_vgpu *vgpu, int bar)
> @@ -1675,7 +1630,6 @@ static int intel_vgpu_probe(struct mdev_device *mdev)
>  		return PTR_ERR(vgpu);
>  	}
>  
> -	INIT_WORK(&vgpu->release_work, intel_vgpu_release_work);
>  	vfio_init_group_dev(&vgpu->vfio_device, &mdev->dev,
>  			    &intel_vgpu_dev_ops);
>  
> @@ -1713,7 +1667,7 @@ static struct mdev_driver intel_vgpu_mdev_driver = {
>  
>  int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
>  {
> -	struct kvm *kvm = info->kvm;
> +	struct kvm *kvm = info->vfio_device.kvm;
>  	struct kvm_memory_slot *slot;
>  	int idx;
>  
> @@ -1743,7 +1697,7 @@ int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
>  
>  int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
>  {
> -	struct kvm *kvm = info->kvm;
> +	struct kvm *kvm = info->vfio_device.kvm;
>  	struct kvm_memory_slot *slot;
>  	int idx;
>  
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index e8914024f5b1..a7d2a95796d3 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -1284,25 +1284,6 @@ static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
>  	}
>  }
>  
> -static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
> -				       unsigned long action, void *data)
> -{
> -	int notify_rc = NOTIFY_OK;
> -	struct ap_matrix_mdev *matrix_mdev;
> -
> -	if (action != VFIO_GROUP_NOTIFY_SET_KVM)
> -		return NOTIFY_OK;
> -
> -	matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
> -
> -	if (!data)
> -		vfio_ap_mdev_unset_kvm(matrix_mdev);
> -	else if (vfio_ap_mdev_set_kvm(matrix_mdev, data))
> -		notify_rc = NOTIFY_DONE;
> -
> -	return notify_rc;
> -}
> -
>  static struct vfio_ap_queue *vfio_ap_find_queue(int apqn)
>  {
>  	struct device *dev;
> @@ -1402,11 +1383,10 @@ static int vfio_ap_mdev_open_device(struct vfio_device *vdev)
>  	unsigned long events;
>  	int ret;
>  
> -	matrix_mdev->group_notifier.notifier_call = vfio_ap_mdev_group_notifier;
> -	events = VFIO_GROUP_NOTIFY_SET_KVM;
> +	if (!vdev->kvm)
> +		return -EINVAL;
>  
> -	ret = vfio_register_notifier(vdev, VFIO_GROUP_NOTIFY, &events,
> -				     &matrix_mdev->group_notifier);
> +	ret = vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm);
>  	if (ret)
>  		return ret;
>  
> @@ -1415,12 +1395,11 @@ static int vfio_ap_mdev_open_device(struct vfio_device *vdev)
>  	ret = vfio_register_notifier(vdev, VFIO_IOMMU_NOTIFY, &events,
>  				     &matrix_mdev->iommu_notifier);
>  	if (ret)
> -		goto out_unregister_group;
> +		goto err_kvm;
>  	return 0;
>  
> -out_unregister_group:
> -	vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
> -				 &matrix_mdev->group_notifier);
> +err_kvm:
> +	vfio_ap_mdev_unset_kvm(matrix_mdev);
>  	return ret;
>  }
>  
> @@ -1431,8 +1410,6 @@ static void vfio_ap_mdev_close_device(struct vfio_device *vdev)
>  
>  	vfio_unregister_notifier(vdev, VFIO_IOMMU_NOTIFY,
>  				 &matrix_mdev->iommu_notifier);
> -	vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
> -				 &matrix_mdev->group_notifier);
>  	vfio_ap_mdev_unset_kvm(matrix_mdev);
>  }
>  
> diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
> index 648fcaf8104a..a26efd804d0d 100644
> --- a/drivers/s390/crypto/vfio_ap_private.h
> +++ b/drivers/s390/crypto/vfio_ap_private.h
> @@ -81,8 +81,6 @@ struct ap_matrix {
>   * @node:	allows the ap_matrix_mdev struct to be added to a list
>   * @matrix:	the adapters, usage domains and control domains assigned to the
>   *		mediated matrix device.
> - * @group_notifier: notifier block used for specifying callback function for
> - *		    handling the VFIO_GROUP_NOTIFY_SET_KVM event
>   * @iommu_notifier: notifier block used for specifying callback function for
>   *		    handling the VFIO_IOMMU_NOTIFY_DMA_UNMAP even
>   * @kvm:	the struct holding guest's state
> @@ -94,7 +92,6 @@ struct ap_matrix_mdev {
>  	struct vfio_device vdev;
>  	struct list_head node;
>  	struct ap_matrix matrix;
> -	struct notifier_block group_notifier;
>  	struct notifier_block iommu_notifier;
>  	struct kvm *kvm;
>  	crypto_hook pqap_hook;
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index cfcff7764403..831fc722e3f8 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -1083,10 +1083,21 @@ static struct file *vfio_device_open(struct vfio_device *device)
>  
>  	mutex_lock(&device->dev_set->lock);
>  	device->open_count++;
> -	if (device->open_count == 1 && device->ops->open_device) {
> -		ret = device->ops->open_device(device);
> -		if (ret)
> -			goto err_undo_count;
> +	if (device->open_count == 1) {
> +		/*
> +		 * Here we pass the KVM pointer with the group under the read
> +		 * lock.  If the device driver will use it, it must obtain a
> +		 * reference and release it during close_device.
> +		 */
> +		down_read(&device->group->group_rwsem);
> +		device->kvm = device->group->kvm;
> +
> +		if (device->ops->open_device) {
> +			ret = device->ops->open_device(device);
> +			if (ret)
> +				goto err_undo_count;
> +		}
> +		up_read(&device->group->group_rwsem);
>  	}
>  	mutex_unlock(&device->dev_set->lock);
>  
> @@ -1119,10 +1130,14 @@ static struct file *vfio_device_open(struct vfio_device *device)
>  
>  err_close_device:
>  	mutex_lock(&device->dev_set->lock);
> +	down_read(&device->group->group_rwsem);
>  	if (device->open_count == 1 && device->ops->close_device)
>  		device->ops->close_device(device);
>  err_undo_count:
>  	device->open_count--;
> +	if (device->open_count == 0 && device->kvm)
> +		device->kvm = NULL;
> +	up_read(&device->group->group_rwsem);
>  	mutex_unlock(&device->dev_set->lock);
>  	module_put(device->dev->driver->owner);
>  err_unassign_container:
> @@ -1315,9 +1330,13 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep)
>  
>  	mutex_lock(&device->dev_set->lock);
>  	vfio_assert_device_open(device);
> +	down_read(&device->group->group_rwsem);
>  	if (device->open_count == 1 && device->ops->close_device)
>  		device->ops->close_device(device);
> +	up_read(&device->group->group_rwsem);
>  	device->open_count--;
> +	if (device->open_count == 0)
> +		device->kvm = NULL;
>  	mutex_unlock(&device->dev_set->lock);
>  
>  	module_put(device->dev->driver->owner);
> @@ -1726,8 +1745,8 @@ EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
>   * @file: VFIO group file
>   * @kvm: KVM to link
>   *
> - * The kvm pointer will be forwarded to all the vfio_device's attached to the
> - * VFIO file via the VFIO_GROUP_NOTIFY_SET_KVM notifier.
> + * When a VFIO device is first opened the KVM will be available in
> + * device->kvm if one was associated with the group.
>   */
>  void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
>  {
> @@ -1738,8 +1757,6 @@ void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
>  
>  	down_write(&group->group_rwsem);
>  	group->kvm = kvm;
> -	blocking_notifier_call_chain(&group->notifier,
> -				     VFIO_GROUP_NOTIFY_SET_KVM, kvm);
>  	up_write(&group->group_rwsem);
>  }
>  EXPORT_SYMBOL_GPL(vfio_file_set_kvm);
> @@ -2006,7 +2023,8 @@ static int vfio_register_iommu_notifier(struct vfio_group *group,
>  	struct vfio_iommu_driver *driver;
>  	int ret;
>  
> -	down_read(&group->group_rwsem);
> +	lockdep_assert_held_read(&group->group_rwsem);
> +
>  	container = group->container;
>  	driver = container->iommu_driver;
>  	if (likely(driver && driver->ops->register_notifier))
> @@ -2014,7 +2032,6 @@ static int vfio_register_iommu_notifier(struct vfio_group *group,
>  						     events, nb);
>  	else
>  		ret = -ENOTTY;
> -	up_read(&group->group_rwsem);
>  
>  	return ret;
>  }
> @@ -2026,7 +2043,8 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group,
>  	struct vfio_iommu_driver *driver;
>  	int ret;
>  
> -	down_read(&group->group_rwsem);
> +	lockdep_assert_held_read(&group->group_rwsem);
> +
>  	container = group->container;
>  	driver = container->iommu_driver;
>  	if (likely(driver && driver->ops->unregister_notifier))
> @@ -2034,47 +2052,10 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group,
>  						       nb);
>  	else
>  		ret = -ENOTTY;
> -	up_read(&group->group_rwsem);
>  
>  	return ret;
>  }
>  
> -static int vfio_register_group_notifier(struct vfio_group *group,
> -					unsigned long *events,
> -					struct notifier_block *nb)
> -{
> -	int ret;
> -	bool set_kvm = false;
> -
> -	if (*events & VFIO_GROUP_NOTIFY_SET_KVM)
> -		set_kvm = true;
> -
> -	/* clear known events */
> -	*events &= ~VFIO_GROUP_NOTIFY_SET_KVM;
> -
> -	/* refuse to continue if still events remaining */
> -	if (*events)
> -		return -EINVAL;
> -
> -	ret = blocking_notifier_chain_register(&group->notifier, nb);
> -	if (ret)
> -		return ret;
> -
> -	/*
> -	 * The attaching of kvm and vfio_group might already happen, so
> -	 * here we replay once upon registration.
> -	 */
> -	if (set_kvm) {
> -		down_read(&group->group_rwsem);
> -		if (group->kvm)
> -			blocking_notifier_call_chain(&group->notifier,
> -						     VFIO_GROUP_NOTIFY_SET_KVM,
> -						     group->kvm);
> -		up_read(&group->group_rwsem);
> -	}
> -	return 0;
> -}
> -
>  int vfio_register_notifier(struct vfio_device *device,
>  			   enum vfio_notify_type type, unsigned long *events,
>  			   struct notifier_block *nb)
> @@ -2090,9 +2071,6 @@ int vfio_register_notifier(struct vfio_device *device,
>  	case VFIO_IOMMU_NOTIFY:
>  		ret = vfio_register_iommu_notifier(group, events, nb);
>  		break;
> -	case VFIO_GROUP_NOTIFY:
> -		ret = vfio_register_group_notifier(group, events, nb);
> -		break;
>  	default:
>  		ret = -EINVAL;
>  	}
> @@ -2114,9 +2092,6 @@ int vfio_unregister_notifier(struct vfio_device *device,
>  	case VFIO_IOMMU_NOTIFY:
>  		ret = vfio_unregister_iommu_notifier(group, nb);
>  		break;
> -	case VFIO_GROUP_NOTIFY:
> -		ret = blocking_notifier_chain_unregister(&group->notifier, nb);
> -		break;
>  	default:
>  		ret = -EINVAL;
>  	}
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 45b287826ce6..aa888cc51757 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -36,6 +36,8 @@ struct vfio_device {
>  	struct vfio_device_set *dev_set;
>  	struct list_head dev_set_list;
>  	unsigned int migration_flags;
> +	/* Driver must reference the kvm during open_device or never touch it */
> +	struct kvm *kvm;
>  
>  	/* Members below here are private, not for driver use */
>  	refcount_t refcount;
> @@ -155,15 +157,11 @@ extern int vfio_dma_rw(struct vfio_device *device, dma_addr_t user_iova,
>  /* each type has independent events */
>  enum vfio_notify_type {
>  	VFIO_IOMMU_NOTIFY = 0,
> -	VFIO_GROUP_NOTIFY = 1,
>  };
>  
>  /* events for VFIO_IOMMU_NOTIFY */
>  #define VFIO_IOMMU_NOTIFY_DMA_UNMAP	BIT(0)
>  
> -/* events for VFIO_GROUP_NOTIFY */
> -#define VFIO_GROUP_NOTIFY_SET_KVM	BIT(0)
> -
>  extern int vfio_register_notifier(struct vfio_device *device,
>  				  enum vfio_notify_type type,
>  				  unsigned long *required_events,

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Wang, Zhi A]

On 5/23/22 4:41 PM, Alex Williamson wrote:
> 
> Hi Zhi & Zhenyu,
> 
> Please review gvt changes below, I'd prefer to get your ack included.
> Thanks!
> 
> Alex
> 
> On Thu, 19 May 2022 14:33:11 -0400
> Matthew Rosato <mjrosato@linux.ibm.com> wrote:
> 
>> Rather than relying on a notifier for associating the KVM with
>> the group, let's assume that the association has already been
>> made prior to device_open.  The first time a device is opened
>> associate the group KVM with the device.
>>
>> This fixes a user-triggerable oops in GVT.
>>
>> Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
>> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
>> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
>> ---
>>  drivers/gpu/drm/i915/gvt/gtt.c        |  4 +-
>>  drivers/gpu/drm/i915/gvt/gvt.h        |  3 -
>>  drivers/gpu/drm/i915/gvt/kvmgt.c      | 82 ++++++--------------------
>>  drivers/s390/crypto/vfio_ap_ops.c     | 35 ++---------
>>  drivers/s390/crypto/vfio_ap_private.h |  3 -
>>  drivers/vfio/vfio.c                   | 83 ++++++++++-----------------
>>  include/linux/vfio.h                  |  6 +-
>>  7 files changed, 57 insertions(+), 159 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
>> index 9c5cc2800975..b4f69364f9a1 100644
>> --- a/drivers/gpu/drm/i915/gvt/gtt.c
>> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
>> @@ -51,7 +51,7 @@ static int preallocated_oos_pages = 8192;
>>  
>>  static bool intel_gvt_is_valid_gfn(struct intel_vgpu *vgpu, unsigned long gfn)
>>  {
>> -	struct kvm *kvm = vgpu->kvm;
>> +	struct kvm *kvm = vgpu->vfio_device.kvm;
>>  	int idx;
>>  	bool ret;
>>  
>> @@ -1185,7 +1185,7 @@ static int is_2MB_gtt_possible(struct intel_vgpu *vgpu,
>>  
>>  	if (!vgpu->attached)
>>  		return -EINVAL;
>> -	pfn = gfn_to_pfn(vgpu->kvm, ops->get_pfn(entry));
>> +	pfn = gfn_to_pfn(vgpu->vfio_device.kvm, ops->get_pfn(entry));
>>  	if (is_error_noslot_pfn(pfn))
>>  		return -EINVAL;
>>  	return PageTransHuge(pfn_to_page(pfn));
>> diff --git a/drivers/gpu/drm/i915/gvt/gvt.h b/drivers/gpu/drm/i915/gvt/gvt.h
>> index 2af4c83e733c..aee1a45da74b 100644
>> --- a/drivers/gpu/drm/i915/gvt/gvt.h
>> +++ b/drivers/gpu/drm/i915/gvt/gvt.h
>> @@ -227,9 +227,6 @@ struct intel_vgpu {
>>  	struct mutex cache_lock;
>>  
>>  	struct notifier_block iommu_notifier;
>> -	struct notifier_block group_notifier;
>> -	struct kvm *kvm;
>> -	struct work_struct release_work;
>>  	atomic_t released;
>>  
>>  	struct kvm_page_track_notifier_node track_node;
>> diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
>> index 7655ffa97d51..e2f6c56ab342 100644
>> --- a/drivers/gpu/drm/i915/gvt/kvmgt.c
>> +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
>> @@ -228,8 +228,6 @@ static void intel_gvt_cleanup_vgpu_type_groups(struct intel_gvt *gvt)
>>  	}
>>  }
>>  
>> -static void intel_vgpu_release_work(struct work_struct *work);
>> -
>>  static void gvt_unpin_guest_page(struct intel_vgpu *vgpu, unsigned long gfn,
>>  		unsigned long size)
>>  {
>> @@ -761,23 +759,6 @@ static int intel_vgpu_iommu_notifier(struct notifier_block *nb,
>>  	return NOTIFY_OK;
>>  }
>>  
>> -static int intel_vgpu_group_notifier(struct notifier_block *nb,
>> -				     unsigned long action, void *data)
>> -{
>> -	struct intel_vgpu *vgpu =
>> -		container_of(nb, struct intel_vgpu, group_notifier);
>> -
>> -	/* the only action we care about */
>> -	if (action == VFIO_GROUP_NOTIFY_SET_KVM) {
>> -		vgpu->kvm = data;
>> -
>> -		if (!data)
>> -			schedule_work(&vgpu->release_work);
>> -	}
>> -
>> -	return NOTIFY_OK;
>> -}
>> -
>>  static bool __kvmgt_vgpu_exist(struct intel_vgpu *vgpu)
>>  {
>>  	struct intel_vgpu *itr;
>> @@ -789,7 +770,7 @@ static bool __kvmgt_vgpu_exist(struct intel_vgpu *vgpu)
>>  		if (!itr->attached)
>>  			continue;
>>  
>> -		if (vgpu->kvm == itr->kvm) {
>> +		if (vgpu->vfio_device.kvm == itr->vfio_device.kvm) {
>>  			ret = true;
>>  			goto out;
>>  		}
>> @@ -806,7 +787,6 @@ static int intel_vgpu_open_device(struct vfio_device *vfio_dev)
>>  	int ret;
>>  
>>  	vgpu->iommu_notifier.notifier_call = intel_vgpu_iommu_notifier;
>> -	vgpu->group_notifier.notifier_call = intel_vgpu_group_notifier;
>>  
>>  	events = VFIO_IOMMU_NOTIFY_DMA_UNMAP;
>>  	ret = vfio_register_notifier(vfio_dev, VFIO_IOMMU_NOTIFY, &events,
>> @@ -817,38 +797,32 @@ static int intel_vgpu_open_device(struct vfio_device *vfio_dev)
>>  		goto out;
>>  	}
>>  
>> -	events = VFIO_GROUP_NOTIFY_SET_KVM;
>> -	ret = vfio_register_notifier(vfio_dev, VFIO_GROUP_NOTIFY, &events,
>> -				     &vgpu->group_notifier);
>> -	if (ret != 0) {
>> -		gvt_vgpu_err("vfio_register_notifier for group failed: %d\n",
>> -			ret);
>> -		goto undo_iommu;
>> -	}
>> -
>>  	ret = -EEXIST;
>>  	if (vgpu->attached)
>> -		goto undo_register;
>> +		goto undo_iommu;
>>  
>>  	ret = -ESRCH;
>> -	if (!vgpu->kvm || vgpu->kvm->mm != current->mm) {
>> +	if (!vgpu->vfio_device.kvm ||
>> +	    vgpu->vfio_device.kvm->mm != current->mm) {
>>  		gvt_vgpu_err("KVM is required to use Intel vGPU\n");
>> -		goto undo_register;
>> +		goto undo_iommu;
>>  	}
>>  
>> +	kvm_get_kvm(vgpu->vfio_device.kvm);
>> +
>>  	ret = -EEXIST;
>>  	if (__kvmgt_vgpu_exist(vgpu))
>> -		goto undo_register;
>> +		goto undo_iommu;
>>  
>>  	vgpu->attached = true;
>> -	kvm_get_kvm(vgpu->kvm);
>>  
>>  	kvmgt_protect_table_init(vgpu);
>>  	gvt_cache_init(vgpu);
>>  
>>  	vgpu->track_node.track_write = kvmgt_page_track_write;
>>  	vgpu->track_node.track_flush_slot = kvmgt_page_track_flush_slot;
>> -	kvm_page_track_register_notifier(vgpu->kvm, &vgpu->track_node);
>> +	kvm_page_track_register_notifier(vgpu->vfio_device.kvm,
>> +					 &vgpu->track_node);
>>  
>>  	debugfs_create_ulong(KVMGT_DEBUGFS_FILENAME, 0444, vgpu->debugfs,
>>  			     &vgpu->nr_cache_entries);
>> @@ -858,10 +832,6 @@ static int intel_vgpu_open_device(struct vfio_device *vfio_dev)
>>  	atomic_set(&vgpu->released, 0);
>>  	return 0;
>>  
>> -undo_register:
>> -	vfio_unregister_notifier(vfio_dev, VFIO_GROUP_NOTIFY,
>> -				 &vgpu->group_notifier);
>> -
>>  undo_iommu:
>>  	vfio_unregister_notifier(vfio_dev, VFIO_IOMMU_NOTIFY,
>>  				 &vgpu->iommu_notifier);
>> @@ -880,8 +850,9 @@ static void intel_vgpu_release_msi_eventfd_ctx(struct intel_vgpu *vgpu)
>>  	}
>>  }
>>  
>> -static void __intel_vgpu_release(struct intel_vgpu *vgpu)
>> +static void intel_vgpu_close_device(struct vfio_device *vfio_dev)
>>  {
>> +	struct intel_vgpu *vgpu = vfio_dev_to_vgpu(vfio_dev);
>>  	struct drm_i915_private *i915 = vgpu->gvt->gt->i915;
>>  	int ret;
>>  
>> @@ -898,35 +869,19 @@ static void __intel_vgpu_release(struct intel_vgpu *vgpu)
>>  	drm_WARN(&i915->drm, ret,
>>  		 "vfio_unregister_notifier for iommu failed: %d\n", ret);
>>  
>> -	ret = vfio_unregister_notifier(&vgpu->vfio_device, VFIO_GROUP_NOTIFY,
>> -				       &vgpu->group_notifier);
>> -	drm_WARN(&i915->drm, ret,
>> -		 "vfio_unregister_notifier for group failed: %d\n", ret);
>> -
>>  	debugfs_remove(debugfs_lookup(KVMGT_DEBUGFS_FILENAME, vgpu->debugfs));
>>  
>> -	kvm_page_track_unregister_notifier(vgpu->kvm, &vgpu->track_node);
>> -	kvm_put_kvm(vgpu->kvm);
>> +	kvm_page_track_unregister_notifier(vgpu->vfio_device.kvm,
>> +					   &vgpu->track_node);
>>  	kvmgt_protect_table_destroy(vgpu);
>>  	gvt_cache_destroy(vgpu);
>>  
>>  	intel_vgpu_release_msi_eventfd_ctx(vgpu);
>>  
>> -	vgpu->kvm = NULL;
>>  	vgpu->attached = false;
>> -}
>> -
>> -static void intel_vgpu_close_device(struct vfio_device *vfio_dev)
>> -{
>> -	__intel_vgpu_release(vfio_dev_to_vgpu(vfio_dev));
>> -}
>> -
>> -static void intel_vgpu_release_work(struct work_struct *work)
>> -{
>> -	struct intel_vgpu *vgpu =
>> -		container_of(work, struct intel_vgpu, release_work);
>>  
>> -	__intel_vgpu_release(vgpu);
>> +	if (vgpu->vfio_device.kvm)
>> +		kvm_put_kvm(vgpu->vfio_device.kvm);
>>  }
>>  
>>  static u64 intel_vgpu_get_bar_addr(struct intel_vgpu *vgpu, int bar)
>> @@ -1675,7 +1630,6 @@ static int intel_vgpu_probe(struct mdev_device *mdev)
>>  		return PTR_ERR(vgpu);
>>  	}
>>  
>> -	INIT_WORK(&vgpu->release_work, intel_vgpu_release_work);
>>  	vfio_init_group_dev(&vgpu->vfio_device, &mdev->dev,
>>  			    &intel_vgpu_dev_ops);
>>  
>> @@ -1713,7 +1667,7 @@ static struct mdev_driver intel_vgpu_mdev_driver = {
>>  
>>  int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
>>  {
>> -	struct kvm *kvm = info->kvm;
>> +	struct kvm *kvm = info->vfio_device.kvm;
>>  	struct kvm_memory_slot *slot;
>>  	int idx;
>>  
>> @@ -1743,7 +1697,7 @@ int intel_gvt_page_track_add(struct intel_vgpu *info, u64 gfn)
>>  
>>  int intel_gvt_page_track_remove(struct intel_vgpu *info, u64 gfn)
>>  {
>> -	struct kvm *kvm = info->kvm;
>> +	struct kvm *kvm = info->vfio_device.kvm;
>>  	struct kvm_memory_slot *slot;
>>  	int idx;
>>  
>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
>> index e8914024f5b1..a7d2a95796d3 100644
>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>> @@ -1284,25 +1284,6 @@ static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
>>  	}
>>  }
>>  
>> -static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
>> -				       unsigned long action, void *data)
>> -{
>> -	int notify_rc = NOTIFY_OK;
>> -	struct ap_matrix_mdev *matrix_mdev;
>> -
>> -	if (action != VFIO_GROUP_NOTIFY_SET_KVM)
>> -		return NOTIFY_OK;
>> -
>> -	matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
>> -
>> -	if (!data)
>> -		vfio_ap_mdev_unset_kvm(matrix_mdev);
>> -	else if (vfio_ap_mdev_set_kvm(matrix_mdev, data))
>> -		notify_rc = NOTIFY_DONE;
>> -
>> -	return notify_rc;
>> -}
>> -
>>  static struct vfio_ap_queue *vfio_ap_find_queue(int apqn)
>>  {
>>  	struct device *dev;
>> @@ -1402,11 +1383,10 @@ static int vfio_ap_mdev_open_device(struct vfio_device *vdev)
>>  	unsigned long events;
>>  	int ret;
>>  
>> -	matrix_mdev->group_notifier.notifier_call = vfio_ap_mdev_group_notifier;
>> -	events = VFIO_GROUP_NOTIFY_SET_KVM;
>> +	if (!vdev->kvm)
>> +		return -EINVAL;
>>  
>> -	ret = vfio_register_notifier(vdev, VFIO_GROUP_NOTIFY, &events,
>> -				     &matrix_mdev->group_notifier);
>> +	ret = vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm);
>>  	if (ret)
>>  		return ret;
>>  
>> @@ -1415,12 +1395,11 @@ static int vfio_ap_mdev_open_device(struct vfio_device *vdev)
>>  	ret = vfio_register_notifier(vdev, VFIO_IOMMU_NOTIFY, &events,
>>  				     &matrix_mdev->iommu_notifier);
>>  	if (ret)
>> -		goto out_unregister_group;
>> +		goto err_kvm;
>>  	return 0;
>>  
>> -out_unregister_group:
>> -	vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
>> -				 &matrix_mdev->group_notifier);
>> +err_kvm:
>> +	vfio_ap_mdev_unset_kvm(matrix_mdev);
>>  	return ret;
>>  }
>>  
>> @@ -1431,8 +1410,6 @@ static void vfio_ap_mdev_close_device(struct vfio_device *vdev)
>>  
>>  	vfio_unregister_notifier(vdev, VFIO_IOMMU_NOTIFY,
>>  				 &matrix_mdev->iommu_notifier);
>> -	vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
>> -				 &matrix_mdev->group_notifier);
>>  	vfio_ap_mdev_unset_kvm(matrix_mdev);
>>  }
>>  
>> diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
>> index 648fcaf8104a..a26efd804d0d 100644
>> --- a/drivers/s390/crypto/vfio_ap_private.h
>> +++ b/drivers/s390/crypto/vfio_ap_private.h
>> @@ -81,8 +81,6 @@ struct ap_matrix {
>>   * @node:	allows the ap_matrix_mdev struct to be added to a list
>>   * @matrix:	the adapters, usage domains and control domains assigned to the
>>   *		mediated matrix device.
>> - * @group_notifier: notifier block used for specifying callback function for
>> - *		    handling the VFIO_GROUP_NOTIFY_SET_KVM event
>>   * @iommu_notifier: notifier block used for specifying callback function for
>>   *		    handling the VFIO_IOMMU_NOTIFY_DMA_UNMAP even
>>   * @kvm:	the struct holding guest's state
>> @@ -94,7 +92,6 @@ struct ap_matrix_mdev {
>>  	struct vfio_device vdev;
>>  	struct list_head node;
>>  	struct ap_matrix matrix;
>> -	struct notifier_block group_notifier;
>>  	struct notifier_block iommu_notifier;
>>  	struct kvm *kvm;
>>  	crypto_hook pqap_hook;
>> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
>> index cfcff7764403..831fc722e3f8 100644
>> --- a/drivers/vfio/vfio.c
>> +++ b/drivers/vfio/vfio.c
>> @@ -1083,10 +1083,21 @@ static struct file *vfio_device_open(struct vfio_device *device)
>>  
>>  	mutex_lock(&device->dev_set->lock);
>>  	device->open_count++;
>> -	if (device->open_count == 1 && device->ops->open_device) {
>> -		ret = device->ops->open_device(device);
>> -		if (ret)
>> -			goto err_undo_count;
>> +	if (device->open_count == 1) {
>> +		/*
>> +		 * Here we pass the KVM pointer with the group under the read
>> +		 * lock.  If the device driver will use it, it must obtain a
>> +		 * reference and release it during close_device.
>> +		 */
>> +		down_read(&device->group->group_rwsem);
>> +		device->kvm = device->group->kvm;
>> +
>> +		if (device->ops->open_device) {
>> +			ret = device->ops->open_device(device);
>> +			if (ret)
>> +				goto err_undo_count;
>> +		}
>> +		up_read(&device->group->group_rwsem);
>>  	}
>>  	mutex_unlock(&device->dev_set->lock);
>>  
>> @@ -1119,10 +1130,14 @@ static struct file *vfio_device_open(struct vfio_device *device)
>>  
>>  err_close_device:
>>  	mutex_lock(&device->dev_set->lock);
>> +	down_read(&device->group->group_rwsem);
>>  	if (device->open_count == 1 && device->ops->close_device)
>>  		device->ops->close_device(device);
>>  err_undo_count:
>>  	device->open_count--;
>> +	if (device->open_count == 0 && device->kvm)
>> +		device->kvm = NULL;
>> +	up_read(&device->group->group_rwsem);
>>  	mutex_unlock(&device->dev_set->lock);
>>  	module_put(device->dev->driver->owner);
>>  err_unassign_container:
>> @@ -1315,9 +1330,13 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep)
>>  
>>  	mutex_lock(&device->dev_set->lock);
>>  	vfio_assert_device_open(device);
>> +	down_read(&device->group->group_rwsem);
>>  	if (device->open_count == 1 && device->ops->close_device)
>>  		device->ops->close_device(device);
>> +	up_read(&device->group->group_rwsem);
>>  	device->open_count--;
>> +	if (device->open_count == 0)
>> +		device->kvm = NULL;
>>  	mutex_unlock(&device->dev_set->lock);
>>  
>>  	module_put(device->dev->driver->owner);
>> @@ -1726,8 +1745,8 @@ EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
>>   * @file: VFIO group file
>>   * @kvm: KVM to link
>>   *
>> - * The kvm pointer will be forwarded to all the vfio_device's attached to the
>> - * VFIO file via the VFIO_GROUP_NOTIFY_SET_KVM notifier.
>> + * When a VFIO device is first opened the KVM will be available in
>> + * device->kvm if one was associated with the group.
>>   */
>>  void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
>>  {
>> @@ -1738,8 +1757,6 @@ void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
>>  
>>  	down_write(&group->group_rwsem);
>>  	group->kvm = kvm;
>> -	blocking_notifier_call_chain(&group->notifier,
>> -				     VFIO_GROUP_NOTIFY_SET_KVM, kvm);
>>  	up_write(&group->group_rwsem);
>>  }
>>  EXPORT_SYMBOL_GPL(vfio_file_set_kvm);
>> @@ -2006,7 +2023,8 @@ static int vfio_register_iommu_notifier(struct vfio_group *group,
>>  	struct vfio_iommu_driver *driver;
>>  	int ret;
>>  
>> -	down_read(&group->group_rwsem);
>> +	lockdep_assert_held_read(&group->group_rwsem);
>> +
>>  	container = group->container;
>>  	driver = container->iommu_driver;
>>  	if (likely(driver && driver->ops->register_notifier))
>> @@ -2014,7 +2032,6 @@ static int vfio_register_iommu_notifier(struct vfio_group *group,
>>  						     events, nb);
>>  	else
>>  		ret = -ENOTTY;
>> -	up_read(&group->group_rwsem);
>>  
>>  	return ret;
>>  }
>> @@ -2026,7 +2043,8 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group,
>>  	struct vfio_iommu_driver *driver;
>>  	int ret;
>>  
>> -	down_read(&group->group_rwsem);
>> +	lockdep_assert_held_read(&group->group_rwsem);
>> +
>>  	container = group->container;
>>  	driver = container->iommu_driver;
>>  	if (likely(driver && driver->ops->unregister_notifier))
>> @@ -2034,47 +2052,10 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group,
>>  						       nb);
>>  	else
>>  		ret = -ENOTTY;
>> -	up_read(&group->group_rwsem);
>>  
>>  	return ret;
>>  }
>>  
>> -static int vfio_register_group_notifier(struct vfio_group *group,
>> -					unsigned long *events,
>> -					struct notifier_block *nb)
>> -{
>> -	int ret;
>> -	bool set_kvm = false;
>> -
>> -	if (*events & VFIO_GROUP_NOTIFY_SET_KVM)
>> -		set_kvm = true;
>> -
>> -	/* clear known events */
>> -	*events &= ~VFIO_GROUP_NOTIFY_SET_KVM;
>> -
>> -	/* refuse to continue if still events remaining */
>> -	if (*events)
>> -		return -EINVAL;
>> -
>> -	ret = blocking_notifier_chain_register(&group->notifier, nb);
>> -	if (ret)
>> -		return ret;
>> -
>> -	/*
>> -	 * The attaching of kvm and vfio_group might already happen, so
>> -	 * here we replay once upon registration.
>> -	 */
>> -	if (set_kvm) {
>> -		down_read(&group->group_rwsem);
>> -		if (group->kvm)
>> -			blocking_notifier_call_chain(&group->notifier,
>> -						     VFIO_GROUP_NOTIFY_SET_KVM,
>> -						     group->kvm);
>> -		up_read(&group->group_rwsem);
>> -	}
>> -	return 0;
>> -}
>> -
>>  int vfio_register_notifier(struct vfio_device *device,
>>  			   enum vfio_notify_type type, unsigned long *events,
>>  			   struct notifier_block *nb)
>> @@ -2090,9 +2071,6 @@ int vfio_register_notifier(struct vfio_device *device,
>>  	case VFIO_IOMMU_NOTIFY:
>>  		ret = vfio_register_iommu_notifier(group, events, nb);
>>  		break;
>> -	case VFIO_GROUP_NOTIFY:
>> -		ret = vfio_register_group_notifier(group, events, nb);
>> -		break;
>>  	default:
>>  		ret = -EINVAL;
>>  	}
>> @@ -2114,9 +2092,6 @@ int vfio_unregister_notifier(struct vfio_device *device,
>>  	case VFIO_IOMMU_NOTIFY:
>>  		ret = vfio_unregister_iommu_notifier(group, nb);
>>  		break;
>> -	case VFIO_GROUP_NOTIFY:
>> -		ret = blocking_notifier_chain_unregister(&group->notifier, nb);
>> -		break;
>>  	default:
>>  		ret = -EINVAL;
>>  	}
>> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
>> index 45b287826ce6..aa888cc51757 100644
>> --- a/include/linux/vfio.h
>> +++ b/include/linux/vfio.h
>> @@ -36,6 +36,8 @@ struct vfio_device {
>>  	struct vfio_device_set *dev_set;
>>  	struct list_head dev_set_list;
>>  	unsigned int migration_flags;
>> +	/* Driver must reference the kvm during open_device or never touch it */
>> +	struct kvm *kvm;
>>  
>>  	/* Members below here are private, not for driver use */
>>  	refcount_t refcount;
>> @@ -155,15 +157,11 @@ extern int vfio_dma_rw(struct vfio_device *device, dma_addr_t user_iova,
>>  /* each type has independent events */
>>  enum vfio_notify_type {
>>  	VFIO_IOMMU_NOTIFY = 0,
>> -	VFIO_GROUP_NOTIFY = 1,
>>  };
>>  
>>  /* events for VFIO_IOMMU_NOTIFY */
>>  #define VFIO_IOMMU_NOTIFY_DMA_UNMAP	BIT(0)
>>  
>> -/* events for VFIO_GROUP_NOTIFY */
>> -#define VFIO_GROUP_NOTIFY_SET_KVM	BIT(0)
>> -
>>  extern int vfio_register_notifier(struct vfio_device *device,
>>  				  enum vfio_notify_type type,
>>  				  unsigned long *required_events,
> 
Acked-by: Zhi Wang <zhi.a.wang@intel.com>

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Alex Williamson]

On Thu, 19 May 2022 14:33:11 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> Rather than relying on a notifier for associating the KVM with
> the group, let's assume that the association has already been
> made prior to device_open.  The first time a device is opened
> associate the group KVM with the device.
> 
> This fixes a user-triggerable oops in GVT.

It seems this has traded an oops for a deadlock, which still exists
today in both GVT-g and vfio-ap.  These are the only vfio drivers that
care about kvm, so they make use of kvm_{get,put}_kvm(), where the
latter is called by their .close_device() callbacks.

.close_device() is called holding the group->group_lock, or at the time
of this commit group->group_rwsem.  The remaining call chain looks like
this:

kvm_put_kvm
 -> kvm_destroy_vm
  -> kvm_destroy_devices
   -> kvm_vfio_destroy
    -> kvm_vfio_file_set_kvm
     -> vfio_file_set_kvm
      -> group->group_lock/group_rwsem

Any suggestions for a fix?  Thanks,

Alex

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Jason Gunthorpe]

On Thu, Jan 05, 2023 at 03:09:30PM -0700, Alex Williamson wrote:
> On Thu, 19 May 2022 14:33:11 -0400
> Matthew Rosato <mjrosato@linux.ibm.com> wrote:
> 
> > Rather than relying on a notifier for associating the KVM with
> > the group, let's assume that the association has already been
> > made prior to device_open.  The first time a device is opened
> > associate the group KVM with the device.
> > 
> > This fixes a user-triggerable oops in GVT.
> 
> It seems this has traded an oops for a deadlock, which still exists
> today in both GVT-g and vfio-ap.  These are the only vfio drivers that
> care about kvm, so they make use of kvm_{get,put}_kvm(), where the
> latter is called by their .close_device() callbacks.

Bleck

It is pretty common to run the final part of 'put' from a workqueue
specifically to avoid stuff like this, eg fput does it

Maybe that is the simplest?

Jason

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Matthew Rosato]

On 1/5/23 6:34 PM, Jason Gunthorpe wrote:
> On Thu, Jan 05, 2023 at 03:09:30PM -0700, Alex Williamson wrote:
>> On Thu, 19 May 2022 14:33:11 -0400
>> Matthew Rosato <mjrosato@linux.ibm.com> wrote:
>>
>>> Rather than relying on a notifier for associating the KVM with
>>> the group, let's assume that the association has already been
>>> made prior to device_open.  The first time a device is opened
>>> associate the group KVM with the device.
>>>
>>> This fixes a user-triggerable oops in GVT.
>>
>> It seems this has traded an oops for a deadlock, which still exists
>> today in both GVT-g and vfio-ap.  These are the only vfio drivers that
>> care about kvm, so they make use of kvm_{get,put}_kvm(), where the

vfio-pci-zdev also

>> latter is called by their .close_device() callbacks.

Huh, I've never seen this deadlock with vfio-pci-zdev or vfio-ap, but I see what you're saying...  I guess it's not seen under typical circumstances with QEMU because kvm_vfio_group_del would have already been triggered via KVM_DEV_VFIO_GROUP_DEL by the time we close the device, such that the group would not be found during the kvm_vfio_destroy call?  (I'm not at all suggesting that we should rely on userspace behaving in this order, just wondering why I never saw it while testing)

> 
> Bleck
> 
> It is pretty common to run the final part of 'put' from a workqueue
> specifically to avoid stuff like this, eg fput does it
> 
> Maybe that is the simplest?

Yeah, this is also what I was thinking, replace the direct kvm_put_kvm calls with, say, schedule_delayed_work in each driver, where the delayed task just does the kvm_put_kvm (along with a brief comment explaining why we handle the put asynchronously).

Other than that..  The goal of this patch originally was to get the kvm reference at first open_device and release it with the very last close_device, so the only other option I could think of would be to take the responsibility back from the vfio drivers and do the kvm_get_kvm and kvm_put_kvm directly in vfio_main after dropping the  (but that would result in some ugly symbol linkage and would acquire kvm references that a driver maybe does not care about so I don't really like that idea)

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Jason Gunthorpe]

On Thu, Jan 05, 2023 at 07:16:37PM -0500, Matthew Rosato wrote:

> Yeah, this is also what I was thinking, replace the direct
> kvm_put_kvm calls with, say, schedule_delayed_work in each driver,
> where the delayed task just does the kvm_put_kvm (along with a brief
> comment explaining why we handle the put asynchronously).

Don't put that in every driver, do something like mmput_async() where
the core code has all of this.

> Other than that..  The goal of this patch originally was to get the
> kvm reference at first open_device and release it with the very last
> close_device, so the only other option I could think of would be to
> take the responsibility back from the vfio drivers and do the
> kvm_get_kvm and kvm_put_kvm directly in vfio_main after dropping the
> (but that would result in some ugly symbol linkage and would acquire
> kvm references that a driver maybe does not care about so I don't
> really like that idea)

And we still have the deadlock problem anyhow..

Jason
 

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Matthew Rosato]

On 1/5/23 7:32 PM, Jason Gunthorpe wrote:
> On Thu, Jan 05, 2023 at 07:16:37PM -0500, Matthew Rosato wrote:
> 
>> Yeah, this is also what I was thinking, replace the direct
>> kvm_put_kvm calls with, say, schedule_delayed_work in each driver,
>> where the delayed task just does the kvm_put_kvm (along with a brief
>> comment explaining why we handle the put asynchronously).
> 
> Don't put that in every driver, do something like mmput_async() where
> the core code has all of this.
> 

If the core vfio code were to add logic to invoke kvm_put_kvm and kvm_get_kvm, won't this introduce a vfio dependency on kvm?  If I recall, we have the drivers handling the kvm reference today in order to avoid that..

>> Other than that..  The goal of this patch originally was to get the
>> kvm reference at first open_device and release it with the very last
>> close_device, so the only other option I could think of would be to
>> take the responsibility back from the vfio drivers and do the
>> kvm_get_kvm and kvm_put_kvm directly in vfio_main after dropping the
>> (but that would result in some ugly symbol linkage and would acquire
>> kvm references that a driver maybe does not care about so I don't
>> really like that idea)
> 
> And we still have the deadlock problem anyhow..

Looks like I never finished my sentence here -- I meant call kvm_put_kvm directly in vfio_main after dropping the group lock (e.g. when we set device->kvm = NULL;). But I think we'd still have the kvm dependency issue

Re: [Intel-gfx] [PATCH v3 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Jason Gunthorpe]

On Thu, Jan 05, 2023 at 08:03:32PM -0500, Matthew Rosato wrote:
> On 1/5/23 7:32 PM, Jason Gunthorpe wrote:
> > On Thu, Jan 05, 2023 at 07:16:37PM -0500, Matthew Rosato wrote:
> > 
> >> Yeah, this is also what I was thinking, replace the direct
> >> kvm_put_kvm calls with, say, schedule_delayed_work in each driver,
> >> where the delayed task just does the kvm_put_kvm (along with a brief
> >> comment explaining why we handle the put asynchronously).
> > 
> > Don't put that in every driver, do something like mmput_async() where
> > the core code has all of this.
> > 
> 
> If the core vfio code were to add logic to invoke kvm_put_kvm and
> kvm_get_kvm, won't this introduce a vfio dependency on kvm?  If I
> recall, we have the drivers handling the kvm reference today in
> order to avoid that..

Not in vfio, put it in kvm 'kvm_put_async()'

Jason