linux-kernel - Re: [PATCH v2 3/8] iommu/vt-d: Implement device

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Message-ID: <20220315143322.GW11336@nvidia.com>
Date:   Tue, 15 Mar 2022 11:33:22 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>
Subject: Re: [PATCH v2 3/8] iommu/vt-d: Implement device_pasid domain attach
 ops

On Mon, Mar 14, 2022 at 10:07:07PM -0700, Jacob Pan wrote:
> +	/*
> +	 * Each domain could have multiple devices attached with shared or per
> +	 * device PASIDs. At the domain level, we keep track of unique PASIDs and
> +	 * device user count.
> +	 * E.g. If a domain has two devices attached, device A has PASID 0, 1;
> +	 * device B has PASID 0, 2. Then the domain would have PASID 0, 1, 2.
> +	 */

A 2d array of xarray's seems like a poor data structure for this task.

AFACIT this wants to store a list of (device, pasid) tuples, so a
simple linked list, 1d xarray vector or a red black tree seems more
appropriate..

> +	if (entry) {
> +		pinfo = entry;
> +	} else {
> +		pinfo = kzalloc(sizeof(*pinfo), GFP_ATOMIC);
> +		if (!pinfo)
> +			return -ENOMEM;
> +		pinfo->pasid = pasid;
> +		/* Store the new PASID info in the per domain array */
> +		ret = xa_err(__xa_store(&dmar_domain->pasids, pasid, pinfo,
> +			     GFP_ATOMIC));
> +		if (ret)
> +			goto xa_store_err;
> +	}
> +	/* Store PASID in per device-domain array, this is for tracking devTLB */
> +	ret = xa_err(xa_store(&info->pasids, pasid, pinfo, GFP_ATOMIC));
> +	if (ret)
> +		goto xa_store_err;
> +
> +	atomic_inc(&pinfo->users);
> +	xa_unlock(&dmar_domain->pasids);
> +
> +	return 0;
> +
> +xa_store_err:
> +	xa_unlock(&dmar_domain->pasids);
> +	spin_lock_irqsave(&iommu->lock, flags);
> +	intel_pasid_tear_down_entry(iommu, dev, pasid, false);
> +	spin_unlock_irqrestore(&iommu->lock, flags);
> +
> +	if (!atomic_read(&pinfo->users)) {
> +		__xa_erase(&dmar_domain->pasids, pasid);

This isn't locked right

Jason