Re: [PATCH v2] vfio: Follow a strict lifetime for struct iommu_group

Christian Borntraeger
2022-10-05T14:19:51Z

Am 05.10.22 um 16:01 schrieb Jason Gunthorpe:
[..]
> commit f8b993620af72fa5f15bd4c1515868013c1c173d
> Author: Jason Gunthorpe <jgg@ziepe.ca>
> Date: Tue Oct 4 13:14:37 2022 -0300
>
> vfio: Make the group FD disassociate from the iommu_group
>
> Allow the vfio_group struct to exist with a NULL iommu_group pointer. When
> the pointer is NULL the vfio_group users promise not to touch the
> iommu_group. This allows a driver to be hot unplugged while userspace is
> keeping the group FD open.
>
> SPAPR mode is excluded from this behavior because of how it wrongly hacks
> part of its iommu interface through KVM. Due to this we loose control over
> what it is doing and cannot revoke the iommu_group usage in the IOMMU
> layer via vfio_group_detach_container().
>
> Thus, for SPAPR the group FDs must still be closed before a device can be
> hot unplugged.
>
> This fixes a userspace regression where we learned that virtnodedevd
> leaves a group FD open even though the /dev/ node for it has been deleted
> and all the drivers for it unplugged.
>
> Fixes: ca5f21b25749 ("vfio: Follow a strict lifetime for struct iommu_group")
> Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Looks better now (I also did a quick check with vfio-pci on s390)

Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>

>
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 59a28251bb0b97..badc9d828cac20 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1313,7 +1313,7 @@ static int vfio_pci_ioctl_pci_hot_reset(struct vfio_pci_core_device *vdev,
> }
>
> /* Ensure the FD is a vfio group FD.*/
> - if (!vfio_file_iommu_group(file)) {
> + if (!vfio_file_is_group(file)) {
> fput(file);
> ret = -EINVAL;
> break;
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index 4d2de02f2ced6e..4e10a281420e66 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -59,6 +59,7 @@ struct vfio_group {
> struct mutex group_lock;
> struct kvm *kvm;
> struct file *opened_file;
> + bool preserve_iommu_group;
> struct swait_queue_head opened_file_wait;
> struct blocking_notifier_head notifier;
> };
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 9b1e5fd5f7b73c..13d22bd84afc47 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -133,6 +133,10 @@ __vfio_group_get_from_iommu(struct iommu_group *iommu_group)
> {
> struct vfio_group *group;
>
> + /*
> + * group->iommu_group from the vfio.group_list cannot be NULL
> + * under the vfio.group_lock.
> + */
> list_for_each_entry(group, &vfio.group_list, vfio_next) {
> if (group->iommu_group == iommu_group) {
> refcount_inc(&group->drivers);
> @@ -159,7 +163,7 @@ static void vfio_group_release(struct device *dev)
>
> mutex_destroy(&group->device_lock);
> mutex_destroy(&group->group_lock);
> - iommu_group_put(group->iommu_group);
> + WARN_ON(group->iommu_group);
> ida_free(&vfio.group_ida, MINOR(group->dev.devt));
> kfree(group);
> }
> @@ -248,6 +252,7 @@ static struct vfio_group *vfio_create_group(struct iommu_group *iommu_group,
> static void vfio_device_remove_group(struct vfio_device *device)
> {
> struct vfio_group *group = device->group;
> + struct iommu_group *iommu_group;
>
> if (group->type == VFIO_NO_IOMMU || group->type == VFIO_EMULATED_IOMMU)
> iommu_group_remove_device(device->dev);
> @@ -265,13 +270,36 @@ static void vfio_device_remove_group(struct vfio_device *device)
> */
> cdev_device_del(&group->cdev, &group->dev);
>
> + mutex_lock(&group->group_lock);
> + /*
> + * These data structures all have paired operations that can only be
> + * undone when the caller holds a live reference on the device. Since
> + * all pairs must be undone these WARN_ON's indicate some caller did not
> + * properly hold the group reference.l.
> + */
> + WARN_ON(!list_empty(&group->device_list));
> + WARN_ON(group->notifier.head);
> +
> + /*
> + * Revoke all users of group->iommu_group. At this point we know there
> + * are no devices active because we are unplugging the last one. Setting
> + * iommu_group to NULL blocks all new users.
> + */
> + if (group->container)
> + vfio_group_detach_container(group);
> + iommu_group = group->iommu_group;
> + group->iommu_group = NULL;
> + mutex_unlock(&group->group_lock);
> +
> /*
> - * Before we allow the last driver in the group to be unplugged the
> - * group must be sanitized so nothing else is or can reference it. This
> - * is because the group->iommu_group pointer should only be used so long
> - * as a device driver is attached to a device in the group.
> + * Normally we can set the iommu_group to NULL above and that will
> + * prevent any users from touching it. However, the SPAPR kvm path takes
> + * a reference to the iommu_group and keeps using it in arch code out
> + * side our control. So if this path is triggred we have no choice but
> + * to wait for the group FD to be closed to be sure everyone has stopped
> + * touching the group.
> */
> - while (group->opened_file) {
> + while (group->preserve_iommu_group && group->opened_file) {
> mutex_unlock(&vfio.group_lock);
> swait_event_idle_exclusive(group->opened_file_wait,
> !group->opened_file);
> @@ -279,17 +307,7 @@ static void vfio_device_remove_group(struct vfio_device *device)
> }
> mutex_unlock(&vfio.group_lock);
>
> - /*
> - * These data structures all have paired operations that can only be
> - * undone when the caller holds a live reference on the group. Since all
> - * pairs must be undone these WARN_ON's indicate some caller did not
> - * properly hold the group reference.
> - */
> - WARN_ON(!list_empty(&group->device_list));
> - WARN_ON(group->container || group->container_users);
> - WARN_ON(group->notifier.head);
> - group->iommu_group = NULL;
> -
> + iommu_group_put(iommu_group);
> put_device(&group->dev);
> }
>
> @@ -531,6 +549,10 @@ static int __vfio_register_dev(struct vfio_device *device,
>
> existing_device = vfio_group_get_device(group, device->dev);
> if (existing_device) {
> + /*
> + * group->iommu_group is non-NULL because we hold the drivers
> + * refcount.
> + */
> dev_WARN(device->dev, "Device already exists on group %d\n",
> iommu_group_id(group->iommu_group));
> vfio_device_put_registration(existing_device);
> @@ -702,6 +724,11 @@ static int vfio_group_ioctl_set_container(struct vfio_group *group,
> ret = -EINVAL;
> goto out_unlock;
> }
> + if (!group->iommu_group) {
> + ret = -ENODEV;
> + goto out_unlock;
> + }
> +
> container = vfio_container_from_file(f.file);
> ret = -EINVAL;
> if (container) {
> @@ -862,6 +889,11 @@ static int vfio_group_ioctl_get_status(struct vfio_group *group,
> status.flags = 0;
>
> mutex_lock(&group->group_lock);
> + if (!group->iommu_group) {
> + mutex_unlock(&group->group_lock);
> + return -ENODEV;
> + }
> +
> if (group->container)
> status.flags |= VFIO_GROUP_FLAGS_CONTAINER_SET |
> VFIO_GROUP_FLAGS_VIABLE;
> @@ -938,13 +970,6 @@ static int vfio_group_fops_release(struct inode *inode, struct file *filep)
> filep->private_data = NULL;
>
> mutex_lock(&group->group_lock);
> - /*
> - * Device FDs hold a group file reference, therefore the group release
> - * is only called when there are no open devices.
> - */
> - WARN_ON(group->notifier.head);
> - if (group->container)
> - vfio_group_detach_container(group);
> group->opened_file = NULL;
> mutex_unlock(&group->group_lock);
> swake_up_one(&group->opened_file_wait);
> @@ -1553,17 +1578,41 @@ static const struct file_operations vfio_device_fops = {
> * @file: VFIO group file
> *
> * The returned iommu_group is valid as long as a ref is held on the file.
> + * This function is deprecated, only the SPAPR path in kvm should call it.
> */
> struct iommu_group *vfio_file_iommu_group(struct file *file)
> {
> struct vfio_group *group = file->private_data;
> + struct iommu_group *iommu_group = NULL;
> +
> + if (!IS_ENABLED(CONFIG_SPAPR_TCE_IOMMU))
> + return NULL;
>
> if (file->f_op != &vfio_group_fops)
> return NULL;
> - return group->iommu_group;
> +
> + mutex_lock(&vfio.group_lock);
> + mutex_lock(&group->group_lock);
> + if (group->iommu_group) {
> + iommu_group = group->iommu_group;
> + group->preserve_iommu_group = true;
> + }
> + mutex_unlock(&group->group_lock);
> + mutex_unlock(&vfio.group_lock);
> + return iommu_group;
> }
> EXPORT_SYMBOL_GPL(vfio_file_iommu_group);
>
> +/**
> + * vfio_file_is_group - True if the file is usable with VFIO aPIS
> + * @file: VFIO group file
> + */
> +bool vfio_file_is_group(struct file *file)
> +{
> + return file->f_op == &vfio_group_fops;
> +}
> +EXPORT_SYMBOL_GPL(vfio_file_is_group);
> +
> /**
> * vfio_file_enforced_coherent - True if the DMA associated with the VFIO file
> * is always CPU cache coherent
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 73bcb92179a224..bd9faaab85de18 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -199,6 +199,7 @@ int vfio_mig_get_next_state(struct vfio_device *device,
> * External user API
> */
> struct iommu_group *vfio_file_iommu_group(struct file *file);
> +bool vfio_file_is_group(struct file *file);
> bool vfio_file_enforced_coherent(struct file *file);
> void vfio_file_set_kvm(struct file *file, struct kvm *kvm);
> bool vfio_file_has_dev(struct file *file, struct vfio_device *device);
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index ce1b01d02c5197..54aec3b0559c70 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -61,6 +61,23 @@ static bool kvm_vfio_file_enforced_coherent(struct file *file)
> return ret;
> }
>
> +static bool kvm_vfio_file_is_group(struct file *file)
> +{
> + bool (*fn)(struct file *file);
> + bool ret;
> +
> + fn = symbol_get(vfio_file_is_group);
> + if (!fn)
> + return false;
> +
> + ret = fn(file);
> +
> + symbol_put(vfio_file_is_group);
> +
> + return ret;
> +}
> +
> +#ifdef CONFIG_SPAPR_TCE_IOMMU
> static struct iommu_group *kvm_vfio_file_iommu_group(struct file *file)
> {
> struct iommu_group *(*fn)(struct file *file);
> @@ -77,7 +94,6 @@ static struct iommu_group *kvm_vfio_file_iommu_group(struct file *file)
> return ret;
> }
>
> -#ifdef CONFIG_SPAPR_TCE_IOMMU
> static void kvm_spapr_tce_release_vfio_group(struct kvm *kvm,
> struct kvm_vfio_group *kvg)
> {
> @@ -136,7 +152,7 @@ static int kvm_vfio_group_add(struct kvm_device *dev, unsigned int fd)
> return -EBADF;
>
> /* Ensure the FD is a vfio group FD.*/
> - if (!kvm_vfio_file_iommu_group(filp)) {
> + if (!kvm_vfio_file_is_group(filp)) {
> ret = -EINVAL;
> goto err_fput;
> }