Re: [PATCH v2 3/7] iommu: Add iommu_report_device_broken() to quarantine a broken device

[Baolu Lu <baolu.lu@linux.intel.com>]

On 3/18/26 03:15, Nicolin Chen wrote:
> When an IOMMU hardware detects an error due to a faulty device (e.g. an ATS
> invalidation timeout), IOMMU drivers may quarantine the device by disabling
> specific hardware features or dropping translation capabilities.
> 
> However, the core-level states of the faulty device are out of sync, as the
> device can be still attached to a translation domain or even potentially be
> moved to a new domain that might overwrite the driver-level quarantine.
> 
> Given that such an error can be likely an ISR, introduce a broken_work per
> iommu_group, and add a helper function to allow driver to report the broken
> device, so as to completely quarantine it in the core.
> 
> Use the existing pci_dev_reset_iommu_prepare() function to shift the device
> to its resetting_domain/blocking_domain. A later pci_dev_reset_iommu_done()
> call will clear it and move it out of the quarantine.
> 
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>   include/linux/iommu.h |  2 ++
>   drivers/iommu/iommu.c | 59 +++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 61 insertions(+)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 9ba12b2164724..9b5f94e566ff9 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -891,6 +891,8 @@ static inline struct iommu_device *__iommu_get_iommu_dev(struct device *dev)
>   #define iommu_get_iommu_dev(dev, type, member) \
>   	container_of(__iommu_get_iommu_dev(dev), type, member)
>   
> +void iommu_report_device_broken(struct device *dev);
> +
>   static inline void iommu_iotlb_gather_init(struct iommu_iotlb_gather *gather)
>   {
>   	*gather = (struct iommu_iotlb_gather) {
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index fcd2902d9e8db..2f297f689a3a3 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -55,6 +55,8 @@ struct iommu_group {
>   	struct list_head devices;
>   	struct xarray pasid_array;
>   	struct mutex mutex;
> +	struct work_struct broken_work;
> +	bool requires_reset;
>   	void *iommu_data;
>   	void (*iommu_data_release)(void *iommu_data);
>   	char *name;
> @@ -146,6 +148,7 @@ static struct group_device *iommu_group_alloc_device(struct iommu_group *group,
>   						     struct device *dev);
>   static void __iommu_group_free_device(struct iommu_group *group,
>   				      struct group_device *grp_dev);
> +static void iommu_group_broken_worker(struct work_struct *work);
>   static void iommu_domain_init(struct iommu_domain *domain, unsigned int type,
>   			      const struct iommu_ops *ops);
>   
> @@ -1057,6 +1060,7 @@ struct iommu_group *iommu_group_alloc(void)
>   	if (!group)
>   		return ERR_PTR(-ENOMEM);
>   
> +	INIT_WORK(&group->broken_work, iommu_group_broken_worker);
>   	group->kobj.kset = iommu_group_kset;
>   	mutex_init(&group->mutex);
>   	INIT_LIST_HEAD(&group->devices);
> @@ -4031,6 +4035,7 @@ void pci_dev_reset_iommu_done(struct pci_dev *pdev)
>   	if (WARN_ON(!group->blocking_domain))
>   		return;
>   
> +	WRITE_ONCE(group->requires_reset, false);
>   	/*
>   	 * A PCI device might have been in an error state, so the IOMMU driver
>   	 * had to quarantine the device by disabling specific hardware feature
> @@ -4062,6 +4067,60 @@ void pci_dev_reset_iommu_done(struct pci_dev *pdev)
>   }
>   EXPORT_SYMBOL_GPL(pci_dev_reset_iommu_done);
>   
> +static void iommu_group_broken_worker(struct work_struct *work)
> +{
> +	struct iommu_group *group =
> +		container_of(work, struct iommu_group, broken_work);
> +	struct pci_dev *pdev = NULL;
> +	struct device *dev;
> +
> +	scoped_guard(mutex, &group->mutex) {
> +		/* Do not block the device again if it has been recovered */
> +		if (!READ_ONCE(group->requires_reset))
> +			goto out_put;
> +		if (list_is_singular(&group->devices)) {
> +			/* Note: only support group with a single device */
> +			dev = iommu_group_first_dev(group);
> +			if (dev_is_pci(dev)) {
> +				pdev = to_pci_dev(dev);
> +				pci_dev_get(pdev);
> +			}
> +		}

The current mechanism is designed only for the PCIe devices within
singleton iommu groups. How about moving the above check to
iommu_report_device_broken() and emitting a message if it is called for
unsupported devices?

> +	}
> +
> +	if (pdev) {
> +		/*
> +		 * Quarantine the device completely. This will be cleared upon
> +		 * a pci_dev_reset_iommu_done() call indicating the recovery.
> +		 */
> +		pci_dev_lock(pdev);
> +		pci_dev_reset_iommu_prepare(pdev);
> +		pci_dev_unlock(pdev);
> +		pci_dev_put(pdev);
> +	}
> +out_put:
> +	iommu_group_put(group);
> +}
> +
> +void iommu_report_device_broken(struct device *dev)
> +{
> +	struct iommu_group *group = iommu_group_get(dev);
> +
> +	if (!group)
> +		return;
> +
> +	if (READ_ONCE(group->requires_reset)) {
> +		iommu_group_put(group);
> +		return;
> +	}
> +	WRITE_ONCE(group->requires_reset, true);
> +
> +	/* Put the group now or later in iommu_group_broken_worker() */
> +	if (!schedule_work(&group->broken_work))
> +		iommu_group_put(group);
> +}
> +EXPORT_SYMBOL_GPL(iommu_report_device_broken);
> +
>   #if IS_ENABLED(CONFIG_IRQ_MSI_IOMMU)
>   /**
>    * iommu_dma_prepare_msi() - Map the MSI page in the IOMMU domain

Thanks,
baolu