linux-kernel - RE: [PATCH v5 1/9] iommu: Introduce domain attachment handle

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Date: Wed, 15 May 2024 07:17:29 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Jason Gunthorpe <jgg@...pe.ca>, Joerg
 Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, Robin Murphy
	<robin.murphy@....com>, Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Nicolin Chen <nicolinc@...dia.com>, "Liu, Yi L" <yi.l.liu@...el.com>, "Jacob
 Pan" <jacob.jun.pan@...ux.intel.com>, Joel Granados <j.granados@...sung.com>
CC: "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"virtualization@...ts.linux-foundation.org"
	<virtualization@...ts.linux-foundation.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Jason Gunthorpe <jgg@...dia.com>
Subject: RE: [PATCH v5 1/9] iommu: Introduce domain attachment handle

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, April 30, 2024 10:57 PM
> 
> +/* Add an attach handle to the group's pasid array. */
> +static struct iommu_attach_handle *
> +iommu_attach_handle_set(struct iommu_domain *domain,
> +			struct iommu_group *group, ioasid_t pasid)
> +{
> +	struct iommu_attach_handle *handle;
> +	void *curr;
> +
> +	handle = kzalloc(sizeof(*handle), GFP_KERNEL);
> +	if (!handle)
> +		return ERR_PTR(-ENOMEM);
> +
> +	handle->domain = domain;
> +	curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, handle,
> GFP_KERNEL);

this could be just xa_insert() which returns -EBUSY if the entry isn't NULL.

> +	if (curr) {
> +		kfree(handle);
> +		return xa_err(curr) ? curr : ERR_PTR(-EBUSY);

'curr' is not an error pointer. You need ERR_PTR(xa_err(curr)).

>  int iommu_attach_group(struct iommu_domain *domain, struct
> iommu_group *group)
>  {
> +	struct iommu_attach_handle *handle;
>  	int ret;
> 
>  	mutex_lock(&group->mutex);
> +	handle = iommu_attach_handle_set(domain, group,
> IOMMU_NO_PASID);
> +	if (IS_ERR(handle)) {
> +		ret = PTR_ERR(handle);
> +		goto out_unlock;
> +	}
>  	ret = __iommu_attach_group(domain, group);
> +	if (ret)
> +		goto out_remove_handle;
>  	mutex_unlock(&group->mutex);

It's slightly better to set the handler after __iommu_attach_group().

doing so is aligned to the sequence in iommu_group_replace_domain().

> @@ -2211,13 +2307,33 @@ EXPORT_SYMBOL_GPL(iommu_attach_group);
>  int iommu_group_replace_domain(struct iommu_group *group,
>  			       struct iommu_domain *new_domain)
>  {
> +	struct iommu_domain *old_domain = group->domain;
> +	struct iommu_attach_handle *handle;
>  	int ret;
> 
>  	if (!new_domain)
>  		return -EINVAL;
> 
> +	if (new_domain == old_domain)
> +		return 0;
> +

__iommu_group_set_domain() already does the check.