Subject: Re: [PATCH v5 4/5] iommu: Introduce iommu_dev_reset_prepare() and iommu_dev_reset_done()

From: Baolu Lu <[email-masked]>
Date: Wed, 12 Nov 2025 14:18:09 +0800

On 11/11/25 13:12, Nicolin Chen wrote:
> +/**
> + * iommu_dev_reset_prepare() - Block IOMMU to prepare for a device reset
> + * @dev: device that is going to enter a reset routine
> + *
> + * When certain device is entering a reset routine, it wants to block any IOMMU
> + * activity during the reset routine. This includes blocking any translation as
> + * well as cache invalidation (especially the device cache).
> + *
> + * This function attaches all RID/PASID of the device's to IOMMU_DOMAIN_BLOCKED
> + * allowing any blocked-domain-supporting IOMMU driver to pause translation and
> + * cahce invalidation, but leaves the software domain pointers intact so later
> + * the iommu_dev_reset_done() can restore everything.
> + *
> + * Return: 0 on success or negative error code if the preparation failed.
> + *
> + * Caller must use iommu_dev_reset_prepare() and iommu_dev_reset_done() together
> + * before/after the core-level reset routine, to unset the resetting_domain.
> + *
> + * These two functions are designed to be used by PCI reset functions that would
> + * not invoke any racy iommu_release_device(), since PCI sysfs node gets removed
> + * before it notifies with a BUS_NOTIFY_REMOVED_DEVICE. When using them in other
> + * case, callers must ensure there will be no racy iommu_release_device() call,
> + * which otherwise would UAF the dev->iommu_group pointer.
> + */
> +int iommu_dev_reset_prepare(struct device *dev)
> +{
> +	struct iommu_group *group = dev->iommu_group;
> +	unsigned long pasid;
> +	void *entry;
> +	int ret = 0;
> +
> +	if (!dev_has_iommu(dev))
> +		return 0;

Nit: This interface is only for PCI layer, so why not just

	if (WARN_ON(!dev_is_pci(dev)))
		return -EINVAL;
?
> +
> +	guard(mutex)(&group->mutex);
> +
> +	/*
> +	 * Once the resetting_domain is set, any concurrent attachment to this
> +	 * iommu_group will be rejected, which would break the attach routines
> +	 * of the sibling devices in the same iommu_group. So, skip this case.
> +	 */
> +	if (dev_is_pci(dev)) {
> +		struct group_device *gdev;
> +
> +		for_each_group_device(group, gdev) {
> +			if (gdev->dev != dev)
> +				return 0;
> +		}
> +	}

With above dev_is_pci() check, here it can simply be,

	if (list_count_nodes(&group->devices) != 1)
		return 0;		

> +
> +	/* Re-entry is not allowed */
> +	if (WARN_ON(group->resetting_domain))
> +		return -EBUSY;
> +
> +	ret = __iommu_group_alloc_blocking_domain(group);
> +	if (ret)
> +		return ret;
> +
> +	/* Stage RID domain at blocking_domain while retaining group->domain */
> +	if (group->domain != group->blocking_domain) {
> +		ret = __iommu_attach_device(group->blocking_domain, dev,
> +					    group->domain);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	/*
> +	 * Stage PASID domains at blocking_domain while retaining pasid_array.
> +	 *
> +	 * The pasid_array is mostly fenced by group->mutex, except one reader
> +	 * in iommu_attach_handle_get(), so it's safe to read without xa_lock.
> +	 */
> +	xa_for_each_start(&group->pasid_array, pasid, entry, 1)
> +		iommu_remove_dev_pasid(dev, pasid,
> +				       pasid_array_entry_to_domain(entry));
> +
> +	group->resetting_domain = group->blocking_domain;
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_dev_reset_prepare);
> +
> +/**
> + * iommu_dev_reset_done() - Restore IOMMU after a device reset is finished
> + * @dev: device that has finished a reset routine
> + *
> + * When certain device has finished a reset routine, it wants to restore its
> + * IOMMU activity, including new translation as well as cache invalidation, by
> + * re-attaching all RID/PASID of the device's back to the domains retained in
> + * the core-level structure.
> + *
> + * Caller must pair it with a successfully returned iommu_dev_reset_prepare().
> + *
> + * Note that, although unlikely, there is a risk that re-attaching domains might
> + * fail due to some unexpected happening like OOM.
> + */
> +void iommu_dev_reset_done(struct device *dev)
> +{
> +	struct iommu_group *group = dev->iommu_group;
> +	unsigned long pasid;
> +	void *entry;
> +
> +	if (!dev_has_iommu(dev))
> +		return;
> +
> +	guard(mutex)(&group->mutex);
> +
> +	/* iommu_dev_reset_prepare() was bypassed for the device */
> +	if (!group->resetting_domain)
> +		return;
> +
> +	/* iommu_dev_reset_prepare() was not successfully called */
> +	if (WARN_ON(!group->blocking_domain))
> +		return;
> +
> +	/* Re-attach RID domain back to group->domain */
> +	if (group->domain != group->blocking_domain) {
> +		WARN_ON(__iommu_attach_device(group->domain, dev,
> +					      group->blocking_domain));
> +	}
> +
> +	/*
> +	 * Re-attach PASID domains back to the domains retained in pasid_array.
> +	 *
> +	 * The pasid_array is mostly fenced by group->mutex, except one reader
> +	 * in iommu_attach_handle_get(), so it's safe to read without xa_lock.
> +	 */
> +	xa_for_each_start(&group->pasid_array, pasid, entry, 1)
> +		WARN_ON(__iommu_set_group_pasid(
> +			pasid_array_entry_to_domain(entry), group, pasid,
> +			group->blocking_domain));
> +
> +	group->resetting_domain = NULL;
> +}
> +EXPORT_SYMBOL_GPL(iommu_dev_reset_done);
> +
>   #if IS_ENABLED(CONFIG_IRQ_MSI_IOMMU)
>   /**
>    * iommu_dma_prepare_msi() - Map the MSI page in the IOMMU domain

Thanks,
baolu