Re: [PATCH v5 1/6] iommu/s390: Fix duplicate domain attachments

[Matthew Rosato]

On 10/6/22 10:46 AM, Niklas Schnelle wrote:
> Since commit fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev
> calls") we can end up with duplicates in the list of devices attached to
> a domain. This is inefficient and confusing since only one domain can
> actually be in control of the IOMMU translations for a device. Fix this
> by detaching the device from the previous domain, if any, on attach.
> Add a WARN_ON() in case we still have attached devices on freeing the
> domain. While here remove the re-attach on failure dance as it was
> determined to be unlikely to help and may confuse debug and recovery.
> 
> Fixes: fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev calls")
> Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> ---
> v4->v5:
> - Unregister IOAT and set zdev->dma_table on error (Matt)
>
...

>  static int s390_iommu_attach_device(struct iommu_domain *domain,
>  				    struct device *dev)
>  {
> @@ -90,7 +116,7 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
>  	struct zpci_dev *zdev = to_zpci_dev(dev);
>  	struct s390_domain_device *domain_device;
>  	unsigned long flags;
> -	int cc, rc;
> +	int cc, rc = 0;
>  
>  	if (!zdev)
>  		return -ENODEV;
> @@ -99,23 +125,17 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
>  	if (!domain_device)
>  		return -ENOMEM;
>  
> -	if (zdev->dma_table && !zdev->s390_domain) {
> -		cc = zpci_dma_exit_device(zdev);
> -		if (cc) {
> -			rc = -EIO;
> -			goto out_free;
> -		}
> -	}
> -
>  	if (zdev->s390_domain)
> -		zpci_unregister_ioat(zdev, 0);
> +		__s390_iommu_detach_device(zdev);
> +	else if (zdev->dma_table)
> +		zpci_dma_exit_device(zdev);
>  
>  	zdev->dma_table = s390_domain->dma_table;
>  	cc = zpci_register_ioat(zdev, 0, zdev->start_dma, zdev->end_dma,
>  				virt_to_phys(zdev->dma_table));
>  	if (cc) {
>  		rc = -EIO;
> -		goto out_restore;
> +		goto out_free;
>  	}

Hmm, with this we will leave attach_dev with a zdev->dma_table associated with this domain (not one generated via zpci_dma_init_device) and zdev->s390_domain == 0.  Won't this cause both s390_domain_free and zpci_dma_exit_device() to try and free the same dma table?

I think we also have to leave with a NULL zdev->dma_table in this case too (you technically could skip the zpci_unregister_ioat)

>  
>  	spin_lock_irqsave(&s390_domain->list_lock, flags);
> @@ -127,9 +147,9 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
>  	/* Allow only devices with identical DMA range limits */
>  	} else if (domain->geometry.aperture_start != zdev->start_dma ||
>  		   domain->geometry.aperture_end != zdev->end_dma) {
> -		rc = -EINVAL;
>  		spin_unlock_irqrestore(&s390_domain->list_lock, flags);
> -		goto out_restore;
> +		rc = -EINVAL;
> +		goto out_unregister;
>  	}
>  	domain_device->zdev = zdev;
>  	zdev->s390_domain = s390_domain;
> @@ -138,14 +158,9 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
>  
>  	return 0;
>  
> -out_restore:
> -	if (!zdev->s390_domain) {
> -		zpci_dma_init_device(zdev);
> -	} else {
> -		zdev->dma_table = zdev->s390_domain->dma_table;
> -		zpci_register_ioat(zdev, 0, zdev->start_dma, zdev->end_dma,
> -				   virt_to_phys(zdev->dma_table));
> -	}
> +out_unregister:
> +	zpci_unregister_ioat(zdev, 0);
> +	zdev->dma_table = NULL;
>  out_free:
>  	kfree(domain_device);
>