Re: [PATCH v2 3/8] vfio: Change vfio_external_user_iommu_id() to vfio_file_iommu_group()

Yi Liu <yi.l.liu@xxxxxxxxx> · Thu, 21 Apr 2022 22:57:06 +0800

On 2022/4/21 03:23, Jason Gunthorpe wrote:
The only user wants to get a pointer to the struct iommu_group associated
with the VFIO group file being used. 

Not native speaker, but above line is a little bit difficlut to interpret.

"What user wants is to get a pointer to the struct iommu_group associated
with the VFIO group file being used."

Reviewed-by: Yi Liu <yi.l.liu@xxxxxxxxx>

Instead of returning the group ID
then searching sysfs for that string just directly return the iommu_group
pointer already held by the vfio_group struct.

It already has a safe lifetime due to the struct file kref, the vfio_group
and thus the iommu_group cannot be destroyed while the group file is open.

Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
  drivers/vfio/vfio.c  | 21 ++++++++++++++-------
  include/linux/vfio.h |  2 +-
  virt/kvm/vfio.c      | 37 ++++++++++++-------------------------
  3 files changed, 27 insertions(+), 33 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index a4555014bd1e72..3444d36714e933 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -1919,10 +1919,7 @@ static const struct file_operations vfio_device_fops = {
   * increments the container user counter to prevent
   * the VFIO group from disposal before KVM exits.
   *
- * 3. The external user calls vfio_external_user_iommu_id()
- * to know an IOMMU ID.
- *
- * 4. When the external KVM finishes, it calls
+ * 3. When the external KVM finishes, it calls
   * vfio_group_put_external_user() to release the VFIO group.
   * This call decrements the container user counter.
   */
@@ -2001,11 +1998,21 @@ bool vfio_external_group_match_file(struct vfio_group *test_group,
  }
  EXPORT_SYMBOL_GPL(vfio_external_group_match_file);
  
-int vfio_external_user_iommu_id(struct vfio_group *group)
+/**
+ * vfio_file_iommu_group - Return the struct iommu_group for the vfio group file
+ * @file: VFIO group file
+ *
+ * The returned iommu_group is valid as long as a ref is held on the file.
+ */
+struct iommu_group *vfio_file_iommu_group(struct file *file)
  {
-	return iommu_group_id(group->iommu_group);
+	struct vfio_group *group = file->private_data;
+
+	if (file->f_op != &vfio_group_fops)
+		return NULL;
+	return group->iommu_group;
  }
-EXPORT_SYMBOL_GPL(vfio_external_user_iommu_id);
+EXPORT_SYMBOL_GPL(vfio_file_iommu_group);
  
  long vfio_external_check_extension(struct vfio_group *group, unsigned long arg)
  {
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 66dda06ec42d1b..8b53fd9920d24a 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -144,7 +144,7 @@ extern struct vfio_group *vfio_group_get_external_user_from_dev(struct device
  								*dev);
  extern bool vfio_external_group_match_file(struct vfio_group *group,
  					   struct file *filep);
-extern int vfio_external_user_iommu_id(struct vfio_group *group);
+extern struct iommu_group *vfio_file_iommu_group(struct file *file);
  extern long vfio_external_check_extension(struct vfio_group *group,
  					  unsigned long arg);
  
diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
index 07ee54a62b560d..1655d3aebd16b4 100644
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -108,43 +108,31 @@ static bool kvm_vfio_group_is_coherent(struct vfio_group *vfio_group)
  }
  
  #ifdef CONFIG_SPAPR_TCE_IOMMU
-static int kvm_vfio_external_user_iommu_id(struct vfio_group *vfio_group)
+static struct iommu_group *kvm_vfio_file_iommu_group(struct file *file)
  {
-	int (*fn)(struct vfio_group *);
-	int ret = -EINVAL;
+	struct iommu_group *(*fn)(struct file *file);
+	struct iommu_group *ret;
  
-	fn = symbol_get(vfio_external_user_iommu_id);
+	fn = symbol_get(vfio_file_iommu_group);
  	if (!fn)
-		return ret;
+		return NULL;
  
-	ret = fn(vfio_group);
+	ret = fn(file);
  
-	symbol_put(vfio_external_user_iommu_id);
+	symbol_put(vfio_file_iommu_group);
  
  	return ret;
  }
  
-static struct iommu_group *kvm_vfio_group_get_iommu_group(
-		struct vfio_group *group)
-{
-	int group_id = kvm_vfio_external_user_iommu_id(group);
-
-	if (group_id < 0)
-		return NULL;
-
-	return iommu_group_get_by_id(group_id);
-}
-
  static void kvm_spapr_tce_release_vfio_group(struct kvm *kvm,
-		struct vfio_group *vfio_group)
+					     struct kvm_vfio_group *kvg)
  {
-	struct iommu_group *grp = kvm_vfio_group_get_iommu_group(vfio_group);
+	struct iommu_group *grp = kvm_vfio_file_iommu_group(kvg->file);
  
  	if (WARN_ON_ONCE(!grp))
  		return;
  
  	kvm_spapr_tce_release_iommu_group(kvm, grp);
-	iommu_group_put(grp);
  }
  #endif
  
@@ -258,7 +246,7 @@ static int kvm_vfio_group_del(struct kvm_device *dev, unsigned int fd)
  		list_del(&kvg->node);
  		kvm_arch_end_assignment(dev->kvm);
  #ifdef CONFIG_SPAPR_TCE_IOMMU
-		kvm_spapr_tce_release_vfio_group(dev->kvm, kvg->vfio_group);
+		kvm_spapr_tce_release_vfio_group(dev->kvm, kvg);
  #endif
  		kvm_vfio_group_set_kvm(kvg->vfio_group, NULL);
  		kvm_vfio_group_put_external_user(kvg->vfio_group);
@@ -304,7 +292,7 @@ static int kvm_vfio_group_set_spapr_tce(struct kvm_device *dev,
  		if (kvg->file != f.file)
  			continue;
  
-		grp = kvm_vfio_group_get_iommu_group(kvg->vfio_group);
+		grp = kvm_vfio_file_iommu_group(kvg->file);
  		if (WARN_ON_ONCE(!grp)) {
  			ret = -EIO;
  			goto err_fdput;
@@ -312,7 +300,6 @@ static int kvm_vfio_group_set_spapr_tce(struct kvm_device *dev,
  
  		ret = kvm_spapr_tce_attach_iommu_group(dev->kvm, param.tablefd,
  						       grp);
-		iommu_group_put(grp);
  		break;
  	}
  
@@ -386,7 +373,7 @@ static void kvm_vfio_destroy(struct kvm_device *dev)
  
  	list_for_each_entry_safe(kvg, tmp, &kv->group_list, node) {
  #ifdef CONFIG_SPAPR_TCE_IOMMU
-		kvm_spapr_tce_release_vfio_group(dev->kvm, kvg->vfio_group);
+		kvm_spapr_tce_release_vfio_group(dev->kvm, kvg);
  #endif
  		kvm_vfio_group_set_kvm(kvg->vfio_group, NULL);
  		kvm_vfio_group_put_external_user(kvg->vfio_group);

--
Regards,
Yi Liu






