linux-kernel - RE: [PATCH v2 3/3] iommufd/device: Change iommufd_hw_pagetable_has

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Message-ID: <BN9PR11MB527697E1E24784576C3FB7628CD29@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Sun, 29 Jan 2023 09:37:00 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>,
        "jgg@...dia.com" <jgg@...dia.com>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 3/3] iommufd/device: Change
 iommufd_hw_pagetable_has_group to device centric

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Sunday, January 29, 2023 5:18 AM
> 
> -static bool iommufd_hw_pagetable_has_group(struct
> iommufd_hw_pagetable *hwpt,
> -					   struct iommu_group *group)
> +static bool iommufd_hw_pagetable_has_device(struct
> iommufd_hw_pagetable *hwpt,
> +					    struct device *dev)
>  {
> -	struct iommufd_device *cur_dev;
> -
> -	list_for_each_entry(cur_dev, &hwpt->devices, devices_item)
> -		if (cur_dev->group == group)
> -			return true;
> -	return false;
> +	/*
> +	 * iommu_get_domain_for_dev() returns an iommu_group->domain
> ptr, if it
> +	 * is the same domain as the hwpt->domain, it means that this hwpt
> has
> +	 * the iommu_group/device.
> +	 */
> +	return hwpt->domain == iommu_get_domain_for_dev(dev);
>  }

Here we could have three scenarios:

1) the device is attached to blocked domain;
2) the device is attached to hwpt->domain;
3) the device is attached to another hwpt->domain;

if this function returns false then iommufd_device_do_attach() will attach
the device to the specified hwpt. But then it's wrong for 3).

Has 3) been denied in earlier path? If yes at least a WARN_ON for
case 3) makes sense here.

> @@ -385,10 +372,8 @@ void iommufd_device_detach(struct
> iommufd_device *idev)
>  	struct iommufd_hw_pagetable *hwpt = idev->hwpt;
> 
>  	mutex_lock(&hwpt->ioas->mutex);
> -	mutex_lock(&hwpt->devices_lock);
>  	refcount_dec(hwpt->devices_users);
> -	list_del(&idev->devices_item);
> -	if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {
> +	if (iommufd_hw_pagetable_has_device(hwpt, idev->dev)) {
>  		if (refcount_read(hwpt->devices_users) == 1) {
>  			iopt_table_remove_domain(&hwpt->ioas->iopt,
>  						 hwpt->domain);
> @@ -397,7 +382,6 @@ void iommufd_device_detach(struct iommufd_device
> *idev)
>  		iommu_detach_group(hwpt->domain, idev->group);
>  	}

emmm how do we track last device detach in a group? Here the first
device detach already leads to group detach...