linux-kernel - Re: [PATCH v11 07/13] iommu/vt-d: Add SVA domain support

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Date:   Thu, 18 Aug 2022 10:36:02 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhu Tony <tony.zhu@...el.com>, iommu@...ts.linux.dev,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 07/13] iommu/vt-d: Add SVA domain support

On Wed, Aug 17, 2022 at 09:20:18AM +0800, Lu Baolu wrote:

> +static int intel_svm_set_dev_pasid(struct iommu_domain *domain,
> +				   struct device *dev, ioasid_t pasid)
> +{
> +	struct device_domain_info *info = dev_iommu_priv_get(dev);
> +	struct intel_iommu *iommu = info->iommu;
> +	struct iommu_sva *sva;
> +	int ret = 0;
> +
> +	mutex_lock(&pasid_mutex);
> +	/*
> +	 * Detach the domain if a blocking domain is set. Check the
> +	 * right domain type once the IOMMU driver supports a real
> +	 * blocking domain.
> +	 */
> +	if (!domain || domain->type == IOMMU_DOMAIN_UNMANAGED) {
> +		intel_svm_unbind_mm(dev, pasid);

See, I think this is exactly the wrong way to use the ops

The blockin domain ops should have its own function that just
unconditionally calls intel_svm_unbind_mm()

> +	} else {
> +		struct mm_struct *mm = domain->mm;
> +
> +		sva = intel_svm_bind_mm(iommu, dev, mm);
> +		if (IS_ERR(sva))
> +			ret = PTR_ERR(sva);

And similarly the SVA domain should have its own op that does this SVM
call.

Muxing the ops with tests on the domain is an anti-pattern. In fact I
would say any time you see an op testing the domain->type it is very
suspicious.

Jason