linux-kernel - Re: [PATCH v13 4/8] iommu/vt-d: Add bind guest PASID support

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Message-ID: <20200514055930.GD22388@infradead.org>
Date:   Wed, 13 May 2020 22:59:30 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <jic23@...nel.org>
Subject: Re: [PATCH v13 4/8] iommu/vt-d: Add bind guest PASID support

> +	if (dev_is_pci(dev)) {
> +		/* VT-d supports devices with full 20 bit PASIDs only */
> +		if (pci_max_pasids(to_pci_dev(dev)) != PASID_MAX)
> +			return -EINVAL;
> +	} else {
> +		return -ENOTSUPP;
> +	}

This looks strange.  Why not:

	if (!dev_is_pci(dev)) {
		return -ENOTSUPP;

	/* VT-d supports devices with full 20 bit PASIDs only */
	if (pci_max_pasids(to_pci_dev(dev)) != PASID_MAX)
		return -EINVAL;

> +		for_each_svm_dev(sdev, svm, dev) {
> +			/*
> +			 * For devices with aux domains, we should allow multiple
> +			 * bind calls with the same PASID and pdev.
> +			 */
> +			if (iommu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX)) {
> +				sdev->users++;
> +			} else {
> +				dev_warn_ratelimited(dev, "Already bound with PASID %u\n",
> +						svm->pasid);
> +				ret = -EBUSY;
> +			}
> +			goto out;

Is this intentionally a for loop that jumps out of the loop after
the first device?

> +	/*
> +	 * PASID table is per device for better security. Therefore, for
> +	 * each bind of a new device even with an existing PASID, we need to
> +	 * call the nested mode setup function here.
> +	 */
> +	spin_lock(&iommu->lock);
> +	ret = intel_pasid_setup_nested(iommu,
> +				       dev,
> +				       (pgd_t *)data->gpgd,
> +				       data->hpasid,
> +				       &data->vtd,
> +				       dmar_domain,
> +				       data->addr_width);

Why not:

	et = intel_pasid_setup_nested(iommu, dev, (pgd_t *)data->gpgd,
			data->hpasid, &data->vtd, dmar_domain,
			data->addr_width);

?

> +	for_each_svm_dev(sdev, svm, dev) {
> +		ret = 0;

		...

> +		break;
> +	}

Same only looks at the first device style.  Why dos it only care about
the first device?  That needs at least a comment, and probably a
first_svm_dev or so heper to make it explicit.