linux-kernel - RE: [PATCH v2 02/10] iommu: Introduce a new iommu_group_replace

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Message-ID: <BN9PR11MB5276941167B52F7C0A7A4BA68CA39@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 15 Feb 2023 06:10:47 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "shuah@...nel.org" <shuah@...nel.org>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: RE: [PATCH v2 02/10] iommu: Introduce a new
 iommu_group_replace_domain() API

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Wednesday, February 8, 2023 5:18 AM
> 
> +int iommu_group_replace_domain(struct iommu_group *group,
> +			       struct iommu_domain *new_domain)
> +{
> +	int ret;
> +
> +	if (!new_domain)
> +		return -EINVAL;
> +
> +	mutex_lock(&group->mutex);
> +	ret = __iommu_group_set_domain(group, new_domain);
> +	if (ret)
> +		__iommu_group_set_domain(group, group->domain);

Just realize the error unwind is a nop given below:

__iommu_group_set_domain()
{
	if (group->domain == new_domain)
		return 0;

	...

There was an attempt [1] to fix error unwind in iommu_attach_group(), by
temporarily set group->domain to NULL before calling set_domain().

Jason, I wonder why this recovering cannot be done in
__iommu_group_set_domain() directly, e.g.:

	ret = __iommu_group_for_each_dev(group, new_domain,
					  iommu_group_do_attach_device);
	if (ret) {
		__iommu_group_for_each_dev(group, group->domain,
					  iommu_group_do_attach_device);
		return ret;
	}
	group->domain = new_domain;

Thanks,
Kevin

[1] https://lore.kernel.org/linux-iommu/20230215052642.6016-1-vasant.hegde@amd.com/