Re: [PATCH v2] iommu/s390: Fix race with release_device ops

[Niklas Schnelle]

On Fri, 2022-08-26 at 15:47 -0400, Matthew Rosato wrote:
> With commit fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev
> calls") s390-iommu is supposed to handle dynamic switching between IOMMU
> domains and the DMA API handling.  However, this commit does not
> sufficiently handle the case where the device is released via a call
> to the release_device op as it may occur at the same time as an opposing
> attach_dev or detach_dev since the group mutex is not held over
> release_device.  This was observed if the device is deconfigured during a
> small window during vfio-pci initialization and can result in WARNs and
> potential kernel panics.
> 
> Handle this by tracking when the device is probed/released via
> dev_iommu_priv_set/get().  Ensure that once the device is released only
> release_device handles the re-init of the device DMA.
> 
> Fixes: fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev calls")
> Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> ---
> Changes since v1:
> - Use mutex instead of spinlock due to potential sleep (Pierre)
> ---
>  arch/s390/include/asm/pci.h |  1 +
>  arch/s390/pci/pci.c         |  1 +
>  drivers/iommu/s390-iommu.c  | 67 ++++++++++++++++++++++++++++---------
>  3 files changed, 53 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
> index 7b4cdadbc023..8f2041eea741 100644
> --- a/arch/s390/include/asm/pci.h
> +++ b/arch/s390/include/asm/pci.h
> @@ -157,6 +157,7 @@ struct zpci_dev {
>  	/* DMA stuff */
>  	unsigned long	*dma_table;
>  	spinlock_t	dma_table_lock;
> +	struct mutex	dma_domain_lock;
>  	int		tlb_refresh;
>  
>  	spinlock_t	iommu_bitmap_lock;
> diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
> index 73cdc5539384..973edd32ecc9 100644
> --- a/arch/s390/pci/pci.c
> +++ b/arch/s390/pci/pci.c
> @@ -832,6 +832,7 @@ struct zpci_dev *zpci_create_device(u32 fid, u32 fh, enum zpci_state state)
>  	kref_init(&zdev->kref);
>  	mutex_init(&zdev->lock);
>  	mutex_init(&zdev->kzdev_lock);
> +	mutex_init(&zdev->dma_domain_lock);
>  
>  	rc = zpci_init_iommu(zdev);
>  	if (rc)
> diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
> index c898bcbbce11..ffb4e3cee7f6 100644
> --- a/drivers/iommu/s390-iommu.c
> +++ b/drivers/iommu/s390-iommu.c
> @@ -90,15 +90,39 @@ 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;
>  
> +	/* First check compatibility */
> +	spin_lock_irqsave(&s390_domain->list_lock, flags);
> +	/* First device defines the DMA range limits */
> +	if (list_empty(&s390_domain->devices)) {
> +		domain->geometry.aperture_start = zdev->start_dma;
> +		domain->geometry.aperture_end = zdev->end_dma;
> +		domain->geometry.force_aperture = true;
> +	/* 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);
> +	if (rc)
> +		return rc;
> +
>  	domain_device = kzalloc(sizeof(*domain_device), GFP_KERNEL);
>  	if (!domain_device)
>  		return -ENOMEM;
>  
> +	/* Leave now if the device has already been released */
> +	mutex_lock(&zdev->dma_domain_lock);
> +	if (!dev_iommu_priv_get(dev)) {
> +		mutex_unlock(&zdev->dma_domain_lock);
> +		kfree(domain_device);
> +		return 0;
> +	}
> +
>  	if (zdev->dma_table && !zdev->s390_domain) {
>  		cc = zpci_dma_exit_device(zdev);
>  		if (cc) {
> @@ -117,22 +141,11 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
>  		rc = -EIO;
>  		goto out_restore;
>  	}
> +	zdev->s390_domain = s390_domain;
> +	mutex_unlock(&zdev->dma_domain_lock);
>  
>  	spin_lock_irqsave(&s390_domain->list_lock, flags);
> -	/* First device defines the DMA range limits */
> -	if (list_empty(&s390_domain->devices)) {
> -		domain->geometry.aperture_start = zdev->start_dma;
> -		domain->geometry.aperture_end = zdev->end_dma;
> -		domain->geometry.force_aperture = true;
> -	/* 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;
> -	}
>  	domain_device->zdev = zdev;
> -	zdev->s390_domain = s390_domain;
>  	list_add(&domain_device->list, &s390_domain->devices);
>  	spin_unlock_irqrestore(&s390_domain->list_lock, flags);
>  
> @@ -147,6 +160,7 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
>  				   virt_to_phys(zdev->dma_table));
>  	}
>  out_free:
> +	mutex_unlock(&zdev->dma_domain_lock);
>  	kfree(domain_device);
>  
>  	return rc;
> @@ -176,17 +190,22 @@ static void s390_iommu_detach_device(struct iommu_domain *domain,
>  	}
>  	spin_unlock_irqrestore(&s390_domain->list_lock, flags);
>  
> -	if (found && (zdev->s390_domain == s390_domain)) {
> +	mutex_lock(&zdev->dma_domain_lock);
> +	if (found && (zdev->s390_domain == s390_domain) &&
> +	    dev_iommu_priv_get(dev)) {
>  		zdev->s390_domain = NULL;
>  		zpci_unregister_ioat(zdev, 0);
>  		zpci_dma_init_device(zdev);
>  	}
> +	mutex_unlock(&zdev->dma_domain_lock);
>  }
>  
>  static struct iommu_device *s390_iommu_probe_device(struct device *dev)
>  {
>  	struct zpci_dev *zdev = to_zpci_dev(dev);
>  
> +	dev_iommu_priv_set(dev, zdev);
> +
>  	return &zdev->iommu_dev;
>  }
>  
> @@ -206,10 +225,26 @@ static void s390_iommu_release_device(struct device *dev)
>  	 *
>  	 * So let's call detach_dev from here if it hasn't been called before.
>  	 */
> -	if (zdev && zdev->s390_domain) {
> +	if (zdev) {
> +		/*
> +		 * Clear priv to block further attaches for this device,
> +		 * ensure detaches don't init DMA
> +		 */
> +		mutex_lock(&zdev->dma_domain_lock);
> +		dev_iommu_priv_set(dev, NULL);
> +		mutex_unlock(&zdev->dma_domain_lock);
> +		/* Make sure this device is removed from the domain list */
>  		domain = iommu_get_domain_for_dev(dev);
>  		if (domain)
>  			s390_iommu_detach_device(domain, dev);
> +		/* Now ensure DMA is initialized from here */
> +		mutex_lock(&zdev->dma_domain_lock);
> +		if (zdev->s390_domain) {
> +			zdev->s390_domain = NULL;
> +			zpci_unregister_ioat(zdev, 0);
> +			zpci_dma_init_device(zdev);
> +		}
> +		mutex_unlock(&zdev->dma_domain_lock);
>  	}
>  }
>  

Looks good to me now. Thanks for tackling this! Feel free to add my:

Reviewed-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
Tested-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>