linux-kernel - RE: [PATCH RFC v3 08/12] iommu/sva: Use attach/detach_pasid

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Date:   Tue, 12 Apr 2022 07:19:19 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>
CC:     Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RFC v3 08/12] iommu/sva: Use attach/detach_pasid_dev in
 SVA interfaces

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Sunday, April 10, 2022 6:25 PM
> +struct iommu_sva *
> +iommu_sva_bind_device(struct device *dev, struct mm_struct *mm, void
> *drvdata)
> +{
> +	int ret = -EINVAL;
> +	struct iommu_sva *handle;
> +	struct iommu_domain *domain;
> +	struct iommu_sva_ioas *ioas;
> +
> +	/*
> +	 * TODO: Remove the drvdata parameter after kernel PASID support
> is
> +	 * enabled for the idxd driver.
> +	 */
> +	if (drvdata)
> +		return ERR_PTR(-EOPNOTSUPP);
> +
> +	/* Allocate mm->pasid if necessary. */
> +	ret = iommu_sva_alloc_pasid(mm, 1, (1U << dev->iommu->pasid_bits)
> - 1);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	mutex_lock(&iommu_sva_lock);
> +	ioas = iommu_sva_ioas_get(mm, mm->pasid);
> +	if (!ioas) {
> +		ret = -ENOMEM;

ioas can be NULL for multiple reasons, e.g. :

1) ioas->mm != mm;
2) kzalloc failure;
3) xa_store failure;

It's more sensible to return error from iommu_sva_ioas_get() directly.

> +		goto out_unlock;
> +	}
> +
> +	/* Search for an existing bond. */
> +	list_for_each_entry(handle, &ioas->bonds, node) {
> +		if (handle->dev == dev) {
> +			refcount_inc(&handle->users);
> +			/* No new bond, drop the counter. */
> +			iommu_sva_ioas_put(ioas);
> +			goto out_success;
> +		}
> +	}
> +
> +	handle = kzalloc(sizeof(*handle), GFP_KERNEL);

s/handle/bond/?

> +	if (!handle) {
> +		ret = -ENOMEM;
> +		goto out_put_ioas;
> +	}
> +
> +	/* The reference to ioas will be kept until domain free. */
> +	domain = iommu_sva_alloc_domain(dev, ioas);

Shouldn't we first try whether existing domains are compatible to this
device?

> @@ -1952,6 +1954,7 @@ EXPORT_SYMBOL_GPL(iommu_domain_alloc);
>  void iommu_domain_free(struct iommu_domain *domain)
>  {
>  	iommu_put_dma_cookie(domain);
> +	iommu_sva_ioas_put(domain->sva_ioas);
>  	domain->ops->free(domain);
>  }

is it good to have general iommu_domain_free() to always call a put()
function for a specific domain type? Why cannot it be done before
calling iommu_domain_free() in sva-lib.c?