linux-kernel - Re: [PATCH v2 10/11] iommu/vt-d: Use xarray for global device_domain

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Message-ID: <20220214073820.GF17411@lst.de>
Date:   Mon, 14 Feb 2022 08:38:20 +0100
From:   Christoph Hellwig <hch@....de>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Liu Yi L <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@....de>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 10/11] iommu/vt-d: Use xarray for global
 device_domain_info

>  
>  const struct iommu_ops intel_iommu_ops;
> @@ -903,7 +905,8 @@ static void pgtable_walk(struct intel_iommu *iommu, unsigned long pfn, u8 bus, u
>  	struct dmar_domain *domain;
>  	int offset, level;
>  
> -	info = dmar_search_domain_by_dev_info(iommu->segment, bus, devfn);
> +	info = xa_load(&device_domain_array,
> +		       devi_idx(iommu->segment, bus, devfn));
>  	if (!info || !info->domain) {
>  		pr_info("device [%02x:%02x.%d] not probed\n",
>  			bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
> @@ -1742,14 +1745,14 @@ static int iommu_init_domains(struct intel_iommu *iommu)

Don't we need a rcu critical section here?

> -	list_for_each_entry_safe(info, tmp, &device_domain_list, global) {
> +	rcu_read_lock();
> +	xa_for_each(&device_domain_array, index, info) {
>  		if (info->iommu != iommu)
>  			continue;
>  
> @@ -1758,7 +1761,7 @@ static void disable_dmar_iommu(struct intel_iommu *iommu)
>  
>  		__dmar_remove_one_dev_info(info);
>  	}
> -	spin_unlock_irqrestore(&device_domain_lock, flags);
> +	rcu_read_unlock();

__dmar_remove_one_dev_info asserts that device_domain_lock is held,
which these two hunks remove.

>  	spin_lock_irqsave(&device_domain_lock, flags);
>  	dev_iommu_priv_set(dev, NULL);
> -	list_del(&info->global);
> +	xa_erase(&device_domain_array,
> +		 devi_idx(info->segment, info->bus, info->devfn));
>  	spin_unlock_irqrestore(&device_domain_lock, flags);
>  
>  	kfree(info);

Do we need a kfree_rcu here to allow rcu based access?