[PATCH v5 2/4] iommufd: Add iommufd_access_replace() API

[Nicolin Chen <nicolinc@xxxxxxxxxx>]

Extract all common procedure, between the iommufd_access_attach() API and
the new iommufd_access_replace() API, to an iommufd_access_change_pt()
helper.

Add iommufd_access_replace() function for VFIO emulated pathway to use.

Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
---
 drivers/iommu/iommufd/device.c          | 60 ++++++++++++++++++++-----
 include/linux/iommufd.h                 |  1 +
 tools/testing/selftests/iommu/iommfd*.c |  0
 3 files changed, 50 insertions(+), 11 deletions(-)
 create mode 100644 tools/testing/selftests/iommu/iommfd*.c

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index 012e85fc6d77..3b39b76fbc3b 100644
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -746,39 +746,77 @@ void iommufd_access_detach(struct iommufd_access *access)
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_access_detach, IOMMUFD);
 
-int iommufd_access_attach(struct iommufd_access *access, u32 ioas_id)
+static struct iommufd_ioas *
+iommufd_access_change_pt(struct iommufd_access *access, u32 ioas_id)
 {
 	struct iommufd_ioas *new_ioas;
 	struct iommufd_object *obj;
 	int rc = 0;
 
+	lockdep_assert_held(&access->ioas_lock);
+
+	obj = iommufd_get_object(access->ictx, ioas_id, IOMMUFD_OBJ_IOAS);
+	if (IS_ERR(obj))
+		return (struct iommufd_ioas *)obj;
+	new_ioas = container_of(obj, struct iommufd_ioas, obj);
+
+	rc = iopt_add_access(&new_ioas->iopt, access);
+	if (rc) {
+		iommufd_put_object(obj);
+		return ERR_PTR(rc);
+	}
+	iommufd_ref_to_users(obj);
+	return new_ioas;
+}
+
+int iommufd_access_attach(struct iommufd_access *access, u32 ioas_id)
+{
+	struct iommufd_ioas *new_ioas;
+
 	mutex_lock(&access->ioas_lock);
 	if (access->ioas != NULL && access->ioas->obj.id != ioas_id) {
 		mutex_unlock(&access->ioas_lock);
 		return -EINVAL;
 	}
 
-	obj = iommufd_get_object(access->ictx, ioas_id, IOMMUFD_OBJ_IOAS);
-	if (IS_ERR(obj)) {
+	new_ioas = iommufd_access_change_pt(access, ioas_id);
+	if (IS_ERR(new_ioas)) {
 		mutex_unlock(&access->ioas_lock);
-		return PTR_ERR(obj);
+		return PTR_ERR(new_ioas);
 	}
-	new_ioas = container_of(obj, struct iommufd_ioas, obj);
+	access->ioas = new_ioas;
+	access->ioas_unpin = new_ioas;
+	mutex_unlock(&access->ioas_lock);
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_access_attach, IOMMUFD);
 
-	rc = iopt_add_access(&new_ioas->iopt, access);
-	if (rc) {
+int iommufd_access_replace(struct iommufd_access *access, u32 ioas_id)
+{
+	struct iommufd_ioas *new_ioas;
+
+	mutex_lock(&access->ioas_lock);
+	if (!access->ioas) {
 		mutex_unlock(&access->ioas_lock);
-		iommufd_put_object(obj);
-		return rc;
+		return -ENOENT;
+	}
+	if (access->ioas->obj.id == ioas_id) {
+		mutex_unlock(&access->ioas_lock);
+		return 0;
 	}
-	iommufd_ref_to_users(obj);
 
+	new_ioas = iommufd_access_change_pt(access, ioas_id);
+	if (IS_ERR(new_ioas)) {
+		mutex_unlock(&access->ioas_lock);
+		return PTR_ERR(new_ioas);
+	}
+	__iommufd_access_detach(access);
 	access->ioas = new_ioas;
 	access->ioas_unpin = new_ioas;
 	mutex_unlock(&access->ioas_lock);
 	return 0;
 }
-EXPORT_SYMBOL_NS_GPL(iommufd_access_attach, IOMMUFD);
+EXPORT_SYMBOL_NS_GPL(iommufd_access_replace, IOMMUFD);
 
 /**
  * iommufd_access_notify_unmap - Notify users of an iopt to stop using it
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index 7c79f9b33246..cd7ae5a625fc 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -46,6 +46,7 @@ iommufd_access_create(struct iommufd_ctx *ictx,
 		      const struct iommufd_access_ops *ops, void *data, u32 *id);
 void iommufd_access_destroy(struct iommufd_access *access);
 int iommufd_access_attach(struct iommufd_access *access, u32 ioas_id);
+int iommufd_access_replace(struct iommufd_access *access, u32 ioas_id);
 void iommufd_access_detach(struct iommufd_access *access);
 
 void iommufd_ctx_get(struct iommufd_ctx *ictx);
diff --git a/tools/testing/selftests/iommu/iommfd*.c b/tools/testing/selftests/iommu/iommfd*.c
new file mode 100644
index 000000000000..e69de29bb2d1
-- 
2.40.0