[PATCH v8 2/4] iommufd: Add iommufd_access_replace() API

[Nicolin Chen <nicolinc@xxxxxxxxxx>]

Extract all common procedure, between the iommufd_access_attach API and a
new iommufd_access_replace API, to an iommufd_access_change_pt helper. And
separate an unlocked __iommufd_access_detach to use it in the helper too.

This adds a new iommufd_access_replace() for VFIO emulated pathway to use.

Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
---
 drivers/iommu/iommufd/device.c | 72 ++++++++++++++++++++++++++--------
 include/linux/iommufd.h        |  1 +
 2 files changed, 57 insertions(+), 16 deletions(-)

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index 072912d87f53..1015d6c42e2b 100644
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -757,13 +757,11 @@ void iommufd_access_destroy(struct iommufd_access *access)
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_access_destroy, IOMMUFD);
 
-void iommufd_access_detach(struct iommufd_access *access)
+static void __iommufd_access_detach(struct iommufd_access *access)
 {
 	struct iommufd_ioas *cur_ioas = access->ioas;
 
-	mutex_lock(&access->ioas_lock);
-	if (WARN_ON(!access->ioas))
-		goto out;
+	lockdep_assert_held(&access->ioas_lock);
 	/*
 	 * Set ioas to NULL to block any further iommufd_access_pin_pages().
 	 * iommufd_access_unpin_pages() can continue using access->ioas_unpin.
@@ -777,44 +775,86 @@ void iommufd_access_detach(struct iommufd_access *access)
 	}
 	iopt_remove_access(&cur_ioas->iopt, access);
 	refcount_dec(&cur_ioas->obj.users);
+}
+
+void iommufd_access_detach(struct iommufd_access *access)
+{
+	mutex_lock(&access->ioas_lock);
+	if (WARN_ON(!access->ioas))
+		goto out;
+	__iommufd_access_detach(access);
 out:
 	access->ioas_unpin = NULL;
 	mutex_unlock(&access->ioas_lock);
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_access_detach, IOMMUFD);
 
-int iommufd_access_attach(struct iommufd_access *access, u32 ioas_id)
+static int iommufd_access_change_pt(struct iommufd_access *access, u32 ioas_id)
 {
+	struct iommufd_ioas *cur_ioas = access->ioas;
 	struct iommufd_ioas *new_ioas;
-	int rc = 0;
+	int rc;
 
-	mutex_lock(&access->ioas_lock);
-	if (WARN_ON(access->ioas || access->ioas_unpin)) {
-		mutex_unlock(&access->ioas_lock);
-		return -EINVAL;
-	}
+	lockdep_assert_held(&access->ioas_lock);
 
 	new_ioas = iommufd_get_ioas(access->ictx, ioas_id);
-	if (IS_ERR(new_ioas)) {
-		mutex_unlock(&access->ioas_lock);
+	if (IS_ERR(new_ioas))
 		return PTR_ERR(new_ioas);
-	}
+
+	if (cur_ioas)
+		__iommufd_access_detach(access);
 
 	rc = iopt_add_access(&new_ioas->iopt, access);
 	if (rc) {
-		mutex_unlock(&access->ioas_lock);
 		iommufd_put_object(&new_ioas->obj);
+		if (cur_ioas)
+			WARN_ON(iommufd_access_change_pt(access,
+							 cur_ioas->obj.id));
 		return rc;
 	}
 	iommufd_ref_to_users(&new_ioas->obj);
 
 	access->ioas = new_ioas;
 	access->ioas_unpin = new_ioas;
-	mutex_unlock(&access->ioas_lock);
 	return 0;
 }
+
+int iommufd_access_attach(struct iommufd_access *access, u32 ioas_id)
+{
+	int rc;
+
+	mutex_lock(&access->ioas_lock);
+	if (WARN_ON(access->ioas || access->ioas_unpin)) {
+		mutex_unlock(&access->ioas_lock);
+		return -EINVAL;
+	}
+
+	rc = iommufd_access_change_pt(access, ioas_id);
+	mutex_unlock(&access->ioas_lock);
+	return rc;
+}
 EXPORT_SYMBOL_NS_GPL(iommufd_access_attach, IOMMUFD);
 
+int iommufd_access_replace(struct iommufd_access *access, u32 ioas_id)
+{
+	int rc;
+
+	mutex_lock(&access->ioas_lock);
+	if (!access->ioas) {
+		mutex_unlock(&access->ioas_lock);
+		return -ENOENT;
+	}
+	if (access->ioas->obj.id == ioas_id) {
+		mutex_unlock(&access->ioas_lock);
+		return 0;
+	}
+
+	rc = iommufd_access_change_pt(access, ioas_id);
+	mutex_unlock(&access->ioas_lock);
+	return rc;
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_access_replace, IOMMUFD);
+
 /**
  * iommufd_access_notify_unmap - Notify users of an iopt to stop using it
  * @iopt: iopt to work on
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index 0ac60256b659..ffc3a949f837 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -49,6 +49,7 @@ 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);
-- 
2.41.0