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Message-ID: <a6e42442-d9cb-0d63-bb71-da78a5669a51@linux.ibm.com>
Date:   Wed, 24 Aug 2022 10:37:23 +0200
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Subject: Re: [PATCH] iommu/s390: Fix race with release_device ops
Content-Language: en-US
To:     Matthew Rosato <mjrosato@linux.ibm.com>, iommu@lists.linux.dev
Cc:     linux-s390@vger.kernel.org, schnelle@linux.ibm.com,
        borntraeger@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com,
        gerald.schaefer@linux.ibm.com, agordeev@linux.ibm.com,
        svens@linux.ibm.com, joro@8bytes.org, will@kernel.org,
        robin.murphy@arm.com, jgg@nvidia.com, linux-kernel@vger.kernel.org
References: <20220823203059.81919-1-mjrosato@linux.ibm.com>
From:   Pierre Morel <pmorel@linux.ibm.com>
In-Reply-To: <20220823203059.81919-1-mjrosato@linux.ibm.com>
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On 8/23/22 22:30, 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@linux.ibm.com>
> ---
>   arch/s390/include/asm/pci.h |  1 +
>   arch/s390/pci/pci.c         |  1 +
>   drivers/iommu/s390-iommu.c  | 68 ++++++++++++++++++++++++++++---------
>   3 files changed, 54 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
> index 7b4cdadbc023..1295b6900e4b 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;
> +	spinlock_t	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..61901c1be3cc 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);
> +	spin_lock_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..513a7ebd23b3 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 */
> +	spin_lock_irqsave(&zdev->dma_domain_lock, flags);
> +	if (!dev_iommu_priv_get(dev)) {
> +		spin_unlock_irqrestore(&zdev->dma_domain_lock, flags);
> +		kfree(domain_device);
> +		return 0;
> +	}
> +
>   	if (zdev->dma_table && !zdev->s390_domain) {
>   		cc = zpci_dma_exit_device(zdev);
>   		if (cc) {

Am I wrong? It seems to me that zpci_dma_exit_device here is called with 
the spin_lock locked but this function zpci_dma_exit_device calls vfree 
which may sleep.


> @@ -117,22 +141,11 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
>   		rc = -EIO;
>   		goto out_restore;
>   	}
> +	zdev->s390_domain = s390_domain;
> +	spin_unlock_irqrestore(&zdev->dma_domain_lock, flags);
>   
>   	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:
> +	spin_unlock_irqrestore(&zdev->dma_domain_lock, flags);
>   	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)) {
> +	spin_lock_irqsave(&zdev->dma_domain_lock, flags);
> +	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);
>   	}
> +	spin_unlock_irqrestore(&zdev->dma_domain_lock, flags);
>   }
>   
>   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;
>   }
>   
> @@ -194,6 +213,7 @@ static void s390_iommu_release_device(struct device *dev)
>   {
>   	struct zpci_dev *zdev = to_zpci_dev(dev);
>   	struct iommu_domain *domain;
> +	unsigned long flags;
>   
>   	/*
>   	 * This is a workaround for a scenario where the IOMMU API common code
> @@ -206,10 +226,26 @@ 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
> +		 */
> +		spin_lock_irqsave(&zdev->dma_domain_lock, flags);
> +		dev_iommu_priv_set(dev, NULL);
> +		spin_unlock_irqrestore(&zdev->dma_domain_lock, flags);
> +		/* 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 */
> +		spin_lock_irqsave(&zdev->dma_domain_lock, flags);
> +		if (zdev->s390_domain) {
> +			zdev->s390_domain = NULL;
> +			zpci_unregister_ioat(zdev, 0);
> +			zpci_dma_init_device(zdev);


If I do not make a mistake, zpci_dma_init_device() calls vzalloc() and 
dma_alloc_cpu_table() which both could sleep.


> +		}
> +		spin_unlock_irqrestore(&zdev->dma_domain_lock, flags);
>   	}
>   }
>   
> 

-- 
Pierre Morel
IBM Lab Boeblingen