[PATCH v2] iommu/virtio: Make instance lookup robust

[PATCH v2] iommu/virtio: Make instance lookup robust

[Robin Murphy]

Much like arm-smmu in commit 7d835134d4e1 ("iommu/arm-smmu: Make
instance lookup robust"), virtio-iommu appears to have the same issue
where iommu_device_register() makes the IOMMU instance visible to other
API callers (including itself) straight away, but internally the
instance isn't ready to recognise itself for viommu_probe_device() to
work correctly until after viommu_probe() has returned. This matters a
lot more now that bus_iommu_probe() has the DT/VIOT knowledge to probe
client devices the way that was always intended. Tweak the lookup and
initialisation in much the same way as for arm-smmu, to ensure that what
we register is functional and ready to go.

Cc: stable@vger.kernel.org
Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

v2: Of course generic bus_find_device_by_fwnode() didn't work, since
    it's dev->parent we need to check rather than dev itself, sigh...
---
 drivers/iommu/virtio-iommu.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index 532db1de201b..b39d6f134ab2 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -998,8 +998,7 @@ static void viommu_get_resv_regions(struct device *dev, struct list_head *head)
 	iommu_dma_get_resv_regions(dev, head);
 }
 
-static const struct iommu_ops viommu_ops;
-static struct virtio_driver virtio_iommu_drv;
+static const struct bus_type *virtio_bus_type;
 
 static int viommu_match_node(struct device *dev, const void *data)
 {
@@ -1008,8 +1007,9 @@ static int viommu_match_node(struct device *dev, const void *data)
 
 static struct viommu_dev *viommu_get_by_fwnode(struct fwnode_handle *fwnode)
 {
-	struct device *dev = driver_find_device(&virtio_iommu_drv.driver, NULL,
-						fwnode, viommu_match_node);
+	struct device *dev = bus_find_device(virtio_bus_type, NULL, fwnode,
+					     viommu_match_node);
+
 	put_device(dev);
 
 	return dev ? dev_to_virtio(dev)->priv : NULL;
@@ -1160,6 +1160,9 @@ static int viommu_probe(struct virtio_device *vdev)
 	if (!viommu)
 		return -ENOMEM;
 
+	/* Borrow this for easy lookups later */
+	virtio_bus_type = dev->bus;
+
 	spin_lock_init(&viommu->request_lock);
 	ida_init(&viommu->domain_ids);
 	viommu->dev = dev;
@@ -1229,10 +1232,10 @@ static int viommu_probe(struct virtio_device *vdev)
 	if (ret)
 		goto err_free_vqs;
 
-	iommu_device_register(&viommu->iommu, &viommu_ops, parent_dev);
-
 	vdev->priv = viommu;
 
+	iommu_device_register(&viommu->iommu, &viommu_ops, parent_dev);
+
 	dev_info(dev, "input address: %u bits\n",
 		 order_base_2(viommu->geometry.aperture_end));
 	dev_info(dev, "page mask: %#llx\n", viommu->pgsize_bitmap);
-- 
2.39.2.101.g768bb238c484.dirty

Re: [PATCH v2] iommu/virtio: Make instance lookup robust

[Eric Auger]

Hi Robin,

On 8/14/25 6:47 PM, Robin Murphy wrote:
> Much like arm-smmu in commit 7d835134d4e1 ("iommu/arm-smmu: Make
> instance lookup robust"), virtio-iommu appears to have the same issue
> where iommu_device_register() makes the IOMMU instance visible to other
> API callers (including itself) straight away, but internally the
> instance isn't ready to recognise itself for viommu_probe_device() to
> work correctly until after viommu_probe() has returned. This matters a
> lot more now that bus_iommu_probe() has the DT/VIOT knowledge to probe
> client devices the way that was always intended. Tweak the lookup and
> initialisation in much the same way as for arm-smmu, to ensure that what
> we register is functional and ready to go.
>
> Cc: stable@vger.kernel.org
> Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path")
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

This version works for me. Thanks for the diligent respin.

Tested-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric



> ---
>
> v2: Of course generic bus_find_device_by_fwnode() didn't work, since
>     it's dev->parent we need to check rather than dev itself, sigh...
> ---
>  drivers/iommu/virtio-iommu.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> index 532db1de201b..b39d6f134ab2 100644
> --- a/drivers/iommu/virtio-iommu.c
> +++ b/drivers/iommu/virtio-iommu.c
> @@ -998,8 +998,7 @@ static void viommu_get_resv_regions(struct device *dev, struct list_head *head)
>  	iommu_dma_get_resv_regions(dev, head);
>  }
>  
> -static const struct iommu_ops viommu_ops;
> -static struct virtio_driver virtio_iommu_drv;
> +static const struct bus_type *virtio_bus_type;
>  
>  static int viommu_match_node(struct device *dev, const void *data)
>  {
> @@ -1008,8 +1007,9 @@ static int viommu_match_node(struct device *dev, const void *data)
>  
>  static struct viommu_dev *viommu_get_by_fwnode(struct fwnode_handle *fwnode)
>  {
> -	struct device *dev = driver_find_device(&virtio_iommu_drv.driver, NULL,
> -						fwnode, viommu_match_node);
> +	struct device *dev = bus_find_device(virtio_bus_type, NULL, fwnode,
> +					     viommu_match_node);
> +
>  	put_device(dev);
>  
>  	return dev ? dev_to_virtio(dev)->priv : NULL;
> @@ -1160,6 +1160,9 @@ static int viommu_probe(struct virtio_device *vdev)
>  	if (!viommu)
>  		return -ENOMEM;
>  
> +	/* Borrow this for easy lookups later */
> +	virtio_bus_type = dev->bus;
> +
>  	spin_lock_init(&viommu->request_lock);
>  	ida_init(&viommu->domain_ids);
>  	viommu->dev = dev;
> @@ -1229,10 +1232,10 @@ static int viommu_probe(struct virtio_device *vdev)
>  	if (ret)
>  		goto err_free_vqs;
>  
> -	iommu_device_register(&viommu->iommu, &viommu_ops, parent_dev);
> -
>  	vdev->priv = viommu;
>  
> +	iommu_device_register(&viommu->iommu, &viommu_ops, parent_dev);
> +
>  	dev_info(dev, "input address: %u bits\n",
>  		 order_base_2(viommu->geometry.aperture_end));
>  	dev_info(dev, "page mask: %#llx\n", viommu->pgsize_bitmap);

Re: [PATCH v2] iommu/virtio: Make instance lookup robust

[Eric Auger]

Hi Robin, Joerg,

On 8/14/25 6:47 PM, Robin Murphy wrote:
> Much like arm-smmu in commit 7d835134d4e1 ("iommu/arm-smmu: Make
> instance lookup robust"), virtio-iommu appears to have the same issue
> where iommu_device_register() makes the IOMMU instance visible to other
> API callers (including itself) straight away, but internally the
> instance isn't ready to recognise itself for viommu_probe_device() to
> work correctly until after viommu_probe() has returned. This matters a
> lot more now that bus_iommu_probe() has the DT/VIOT knowledge to probe
> client devices the way that was always intended. Tweak the lookup and
> initialisation in much the same way as for arm-smmu, to ensure that what
> we register is functional and ready to go.
>
> Cc: stable@vger.kernel.org
> Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path")
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

could we get that fix merged as soon as possible? the virtio-iommu is
currently totally broken.

Thanks

Eric
> ---
>
> v2: Of course generic bus_find_device_by_fwnode() didn't work, since
>     it's dev->parent we need to check rather than dev itself, sigh...
> ---
>  drivers/iommu/virtio-iommu.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> index 532db1de201b..b39d6f134ab2 100644
> --- a/drivers/iommu/virtio-iommu.c
> +++ b/drivers/iommu/virtio-iommu.c
> @@ -998,8 +998,7 @@ static void viommu_get_resv_regions(struct device *dev, struct list_head *head)
>  	iommu_dma_get_resv_regions(dev, head);
>  }
>  
> -static const struct iommu_ops viommu_ops;
> -static struct virtio_driver virtio_iommu_drv;
> +static const struct bus_type *virtio_bus_type;
>  
>  static int viommu_match_node(struct device *dev, const void *data)
>  {
> @@ -1008,8 +1007,9 @@ static int viommu_match_node(struct device *dev, const void *data)
>  
>  static struct viommu_dev *viommu_get_by_fwnode(struct fwnode_handle *fwnode)
>  {
> -	struct device *dev = driver_find_device(&virtio_iommu_drv.driver, NULL,
> -						fwnode, viommu_match_node);
> +	struct device *dev = bus_find_device(virtio_bus_type, NULL, fwnode,
> +					     viommu_match_node);
> +
>  	put_device(dev);
>  
>  	return dev ? dev_to_virtio(dev)->priv : NULL;
> @@ -1160,6 +1160,9 @@ static int viommu_probe(struct virtio_device *vdev)
>  	if (!viommu)
>  		return -ENOMEM;
>  
> +	/* Borrow this for easy lookups later */
> +	virtio_bus_type = dev->bus;
> +
>  	spin_lock_init(&viommu->request_lock);
>  	ida_init(&viommu->domain_ids);
>  	viommu->dev = dev;
> @@ -1229,10 +1232,10 @@ static int viommu_probe(struct virtio_device *vdev)
>  	if (ret)
>  		goto err_free_vqs;
>  
> -	iommu_device_register(&viommu->iommu, &viommu_ops, parent_dev);
> -
>  	vdev->priv = viommu;
>  
> +	iommu_device_register(&viommu->iommu, &viommu_ops, parent_dev);
> +
>  	dev_info(dev, "input address: %u bits\n",
>  		 order_base_2(viommu->geometry.aperture_end));
>  	dev_info(dev, "page mask: %#llx\n", viommu->pgsize_bitmap);

Re: [PATCH v2] iommu/virtio: Make instance lookup robust

[Joerg Roedel]

On Thu, Aug 14, 2025 at 05:47:16PM +0100, Robin Murphy wrote:
>  drivers/iommu/virtio-iommu.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)

Applied for -rc, thanks Robin.