linux-kernel - Re: [PATCH v5 5/8] iommufd/vdevice: Remove struct device reference from struct vdevice

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Message-ID: <aHakX0SzQ9/EX3AT@Asurada-Nvidia>
Date: Tue, 15 Jul 2025 11:56:31 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Xu Yilun <yilun.xu@...ux.intel.com>
CC: <jgg@...dia.com>, <jgg@...pe.ca>, <kevin.tian@...el.com>,
	<will@...nel.org>, <aneesh.kumar@...nel.org>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <joro@...tes.org>, <robin.murphy@....com>,
	<shuah@...nel.org>, <aik@....com>, <dan.j.williams@...el.com>,
	<baolu.lu@...ux.intel.com>, <yilun.xu@...el.com>
Subject: Re: [PATCH v5 5/8] iommufd/vdevice: Remove struct device reference
 from struct vdevice

On Tue, Jul 15, 2025 at 02:32:42PM +0800, Xu Yilun wrote:
> diff --git a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
> index eb90af5093d8..8a515987b948 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
> @@ -1218,7 +1218,7 @@ static void tegra241_vintf_destroy_vsid(struct iommufd_vdevice *vdev)
>  
>  static int tegra241_vintf_init_vsid(struct iommufd_vdevice *vdev)
>  {
> -	struct arm_smmu_master *master = dev_iommu_priv_get(vdev->dev);
> +	struct arm_smmu_master *master = dev_iommu_priv_get(vdev->idev->dev);

Hmm, this breaks :(

drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c: In function 'tegra241_vintf_init_vsid':
drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c:1230:71: error: invalid use of undefined type 'struct iommufd_device'
 1230 |         struct arm_smmu_master *master = dev_iommu_priv_get(vdev->idev->dev);

Unfortunately the iommufd_device structure is defined in the
private header that's not shared with any IOMMU driver.

So, we need in the driver.c a new helper that converts a vdev
pointer to dev. Something like:

diff --git a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
index ff6bbd2137146..fd6b083535271 100644
--- a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
+++ b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
@@ -1227,7 +1227,8 @@ static void tegra241_vintf_destroy_vsid(struct iommufd_vdevice *vdev)
 
 static int tegra241_vintf_init_vsid(struct iommufd_vdevice *vdev)
 {
-	struct arm_smmu_master *master = dev_iommu_priv_get(vdev->idev->dev);
+	struct device *dev = iommufd_vdevice_to_device(vdev);
+	struct arm_smmu_master *master = dev_iommu_priv_get(dev);
 	struct tegra241_vintf *vintf = viommu_to_vintf(vdev->viommu);
 	struct tegra241_vintf_sid *vsid = vdev_to_vsid(vdev);
 	struct arm_smmu_stream *stream = &master->streams[0];
diff --git a/drivers/iommu/iommufd/driver.c b/drivers/iommu/iommufd/driver.c
index df25db6d2eafc..6f1010da221c9 100644
--- a/drivers/iommu/iommufd/driver.c
+++ b/drivers/iommu/iommufd/driver.c
@@ -83,6 +83,12 @@ void _iommufd_destroy_mmap(struct iommufd_ctx *ictx,
 }
 EXPORT_SYMBOL_NS_GPL(_iommufd_destroy_mmap, "IOMMUFD");
 
+struct device *iommufd_vdevice_to_device(struct iommufd_vdevice *vdev)
+{
+	return vdev->idev->dev;
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_vdevice_to_device, "IOMMUFD");
+
 /* Caller should xa_lock(&viommu->vdevs) to protect the return value */
 struct device *iommufd_viommu_find_dev(struct iommufd_viommu *viommu,
 				       unsigned long vdev_id)
@@ -92,7 +98,7 @@ struct device *iommufd_viommu_find_dev(struct iommufd_viommu *viommu,
 	lockdep_assert_held(&viommu->vdevs.xa_lock);
 
 	vdev = xa_load(&viommu->vdevs, vdev_id);
-	return vdev ? vdev->idev->dev : NULL;
+	return vdev ? iommufd_vdevice_to_device(vdev) : NULL;
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_viommu_find_dev, "IOMMUFD");
 
@@ -109,7 +115,7 @@ int iommufd_viommu_get_vdev_id(struct iommufd_viommu *viommu,
 
 	xa_lock(&viommu->vdevs);
 	xa_for_each(&viommu->vdevs, index, vdev) {
-		if (vdev->idev->dev == dev) {
+		if (iommufd_vdevice_to_device(vdev) == dev) {
 			*vdev_id = vdev->virt_id;
 			rc = 0;
 			break;
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index 61410a78cbce7..ee88e90021870 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -266,6 +266,7 @@ int _iommufd_alloc_mmap(struct iommufd_ctx *ictx, struct iommufd_object *owner,
 			unsigned long *offset);
 void _iommufd_destroy_mmap(struct iommufd_ctx *ictx,
 			   struct iommufd_object *owner, unsigned long offset);
+struct device *iommufd_vdevice_to_device(struct iommufd_vdevice *vdev);
 struct device *iommufd_viommu_find_dev(struct iommufd_viommu *viommu,
 				       unsigned long vdev_id);
 int iommufd_viommu_get_vdev_id(struct iommufd_viommu *viommu,
@@ -300,6 +301,12 @@ static inline void _iommufd_destroy_mmap(struct iommufd_ctx *ictx,
 {
 }
 
+static inline struct device *
+iommufd_vdevice_to_device(struct iommufd_vdevice *vdev)
+{
+	return ERR_PTR(-ENODEV);
+}
+
 static inline struct device *
 iommufd_viommu_find_dev(struct iommufd_viommu *viommu, unsigned long vdev_id)
 {