linux-kernel - RE: [PATCH v1 3/6] iommu/vt-d: Refactor iommu information of each domain

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Date:   Thu, 30 Jun 2022 08:28:07 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>, Steve Wahl <steve.wahl@....com>
CC:     David Woodhouse <dwmw2@...radead.org>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <sivanich@....com>,
        "Anderson, Russ" <russ.anderson@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1 3/6] iommu/vt-d: Refactor iommu information of each
 domain

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Saturday, June 25, 2022 8:52 PM
> 
> +struct iommu_domain_info {
> +	struct intel_iommu *iommu;
> +	unsigned int refcnt;
> +	u16 did;
> +};
> +
>  struct dmar_domain {
>  	int	nid;			/* node id */
> -
> -	unsigned int iommu_refcnt[DMAR_UNITS_SUPPORTED];
> -					/* Refcount of devices per iommu */
> -
> -
> -	u16		iommu_did[DMAR_UNITS_SUPPORTED];
> -					/* Domain ids per IOMMU. Use u16
> since
> -					 * domain ids are 16 bit wide
> according
> -					 * to VT-d spec, section 9.3 */

It'd make sense to keep the comments when moving above fields.

> +	spin_lock(&iommu->lock);
> +	curr = xa_load(&domain->iommu_array, iommu->seq_id);
> +	if (curr) {
> +		curr->refcnt++;
> +		kfree(info);
> +		goto success;

Not a fan of adding a label for success. Just putting two lines (unlock+
return) here is clearer.

> +	ret = xa_err(xa_store(&domain->iommu_array, iommu->seq_id,
> +			      info, GFP_ATOMIC));

check xa_err in separate line.

> 
>  static void domain_detach_iommu(struct dmar_domain *domain,
>  				struct intel_iommu *iommu)
>  {
> -	int num;
> +	struct iommu_domain_info *info;
> 
>  	spin_lock(&iommu->lock);
> -	domain->iommu_refcnt[iommu->seq_id] -= 1;
> -	if (domain->iommu_refcnt[iommu->seq_id] == 0) {
> -		num = domain->iommu_did[iommu->seq_id];
> -		clear_bit(num, iommu->domain_ids);
> +	info = xa_load(&domain->iommu_array, iommu->seq_id);
> +	if (--info->refcnt == 0) {
> +		clear_bit(info->did, iommu->domain_ids);
> +		xa_erase(&domain->iommu_array, iommu->seq_id);
>  		domain_update_iommu_cap(domain);
> -		domain->iommu_did[iommu->seq_id] = 0;
> +		kfree(info);

domain->nid may still point to the node of the removed iommu.