linux-kernel - Re: [PATCH v7 04/10] iommu: Extend domain attach group with handle support

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Message-ID: <Zn8luxc+RLBOIIX0@ziepe.ca>
Date: Fri, 28 Jun 2024 18:06:03 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: Kevin Tian <kevin.tian@...el.com>, 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>, Yi Liu <yi.l.liu@...el.com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Joel Granados <j.granados@...sung.com>, iommu@...ts.linux.dev,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 04/10] iommu: Extend domain attach group with handle
 support

On Sun, Jun 16, 2024 at 02:11:49PM +0800, Lu Baolu wrote:

> +int iommu_replace_group_handle(struct iommu_group *group,
> +			       struct iommu_domain *new_domain,
> +			       struct iommu_attach_handle *handle)
> +{
> +	struct iommu_domain *old_domain = group->domain;
> +	void *curr;
> +	int ret;
> +
> +	if (!new_domain)
> +		return -EINVAL;
> +
> +	mutex_lock(&group->mutex);
> +	ret = __iommu_group_set_domain(group, new_domain);
> +	if (ret)
> +		goto err_unlock;
> +	xa_erase(&group->pasid_array, IOMMU_NO_PASID);
> +	if (handle) {
> +		curr = xa_store(&group->pasid_array, IOMMU_NO_PASID, handle, GFP_KERNEL);
> +		if (xa_err(curr)) {
> +			ret = xa_err(curr);
> +			goto err_restore;

But this error unwind doesn't work because the xa_erase() already
happened and there may have been a handle there that we don't put
back.

Something like this - store to a reserved entry cannot fail:

int iommu_replace_group_handle(struct iommu_group *group,
			       struct iommu_domain *new_domain,
			       struct iommu_attach_handle *handle)
{
	void *curr;
	int ret;

	if (!new_domain)
		return -EINVAL;

	mutex_lock(&group->mutex);
	if (handle) {
		ret = xa_reserve(&group->pasid_array, IOMMU_NO_PASID,
				 GFP_KERNEL);
		if (ret)
			goto err_unlock;
	}

	ret = __iommu_group_set_domain(group, new_domain);
	if (ret)
		goto err_release;

	curr = xa_store(&group->pasid_array, IOMMU_NO_PASID, handle,
			GFP_KERNEL);
	WARN_ON(xa_is_err(curr));

	mutex_unlock(&group->mutex);

	return 0;
err_release:
	xa_release(&group->pasid_array, IOMMU_NO_PASID);
err_unlock:
	mutex_unlock(&group->mutex);
	return ret;
}

Jason