[PATCH v1 5/8] iommufd: Add replace support in iommufd_access_set_ioas()

[Nicolin Chen <nicolinc@xxxxxxxxxx>]

Support an access->ioas replacement in iommufd_access_set_ioas(), which
sets the access->ioas to NULL provisionally so that any further incoming
iommufd_access_pin_pages() callback can be blocked.

Then, call access->ops->unmap() to clean up the entire iopt. To allow an
iommufd_access_unpin_pages() callback to happen via this unmap() call,
add an ioas_unpin pointer so the unpin routine won't be affected by the
"access->ioas = NULL" trick above.

Also, a vdev without an ops->dma_unmap implementation cannot replace its
access->ioas pointer. So add an iommufd_access_ioas_is_attached() helper
to sanity that.

Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
---
 drivers/iommu/iommufd/device.c          | 28 +++++++++++++++++++++++--
 drivers/iommu/iommufd/iommufd_private.h |  1 +
 drivers/vfio/iommufd.c                  |  4 ++++
 include/linux/iommufd.h                 |  1 +
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index f4bd6f532a90..8118d5262800 100644
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -509,11 +509,23 @@ int iommufd_access_set_ioas(struct iommufd_access *access, u32 ioas_id)
 		iommufd_ref_to_users(obj);
 	}
 
+	/*
+	 * Set ioas to NULL to block any further iommufd_access_pin_pages().
+	 * iommufd_access_unpin_pages() can continue using access->ioas_unpin.
+	 */
+	access->ioas = NULL;
+
 	if (cur_ioas) {
+		if (new_ioas) {
+			mutex_unlock(&access->ioas_lock);
+			access->ops->unmap(access->data, 0, ULONG_MAX);
+			mutex_lock(&access->ioas_lock);
+		}
 		iopt_remove_access(&cur_ioas->iopt, access);
 		refcount_dec(&cur_ioas->obj.users);
 	}
 
+	access->ioas_unpin = new_ioas;
 	access->ioas = new_ioas;
 	mutex_unlock(&access->ioas_lock);
 
@@ -527,6 +539,18 @@ int iommufd_access_set_ioas(struct iommufd_access *access, u32 ioas_id)
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_access_set_ioas, IOMMUFD);
 
+bool iommufd_access_ioas_is_attached(struct iommufd_access *access)
+{
+	bool attached;
+
+	mutex_lock(&access->ioas_lock);
+	attached = !!access->ioas;
+	mutex_unlock(&access->ioas_lock);
+
+	return attached;
+}
+EXPORT_SYMBOL_NS_GPL(iommufd_access_ioas_is_attached, IOMMUFD);
+
 /**
  * iommufd_access_notify_unmap - Notify users of an iopt to stop using it
  * @iopt: iopt to work on
@@ -587,11 +611,11 @@ void iommufd_access_unpin_pages(struct iommufd_access *access,
 		return;
 
 	mutex_lock(&access->ioas_lock);
-	if (!access->ioas) {
+	if (!access->ioas_unpin) {
 		mutex_unlock(&access->ioas_lock);
 		return;
 	}
-	iopt = &access->ioas->iopt;
+	iopt = &access->ioas_unpin->iopt;
 
 	down_read(&iopt->iova_rwsem);
 	iopt_for_each_contig_area(&iter, area, iopt, iova, last_iova)
diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 2f4bb106bac6..593138bb37b8 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -261,6 +261,7 @@ struct iommufd_access {
 	struct iommufd_object obj;
 	struct iommufd_ctx *ictx;
 	struct iommufd_ioas *ioas;
+	struct iommufd_ioas *ioas_unpin;
 	struct mutex ioas_lock;
 	const struct iommufd_access_ops *ops;
 	void *data;
diff --git a/drivers/vfio/iommufd.c b/drivers/vfio/iommufd.c
index 78a8e4641cbf..7e09defbcffe 100644
--- a/drivers/vfio/iommufd.c
+++ b/drivers/vfio/iommufd.c
@@ -187,6 +187,10 @@ int vfio_iommufd_emulated_attach_ioas(struct vfio_device *vdev, u32 *pt_id)
 	if (!vdev->iommufd_access)
 		return -ENOENT;
 
+	if (!vdev->ops->dma_unmap && pt_id &&
+	    iommufd_access_ioas_is_attached(vdev->iommufd_access))
+		return -EBUSY;
+
 	iommufd_access_set_ioas(vdev->iommufd_access, *pt_id);
 	return 0;
 }
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index 0e30f2ce27cd..e8d764b2c14c 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -44,6 +44,7 @@ iommufd_access_create(struct iommufd_ctx *ictx,
 		      const struct iommufd_access_ops *ops, void *data);
 void iommufd_access_destroy(struct iommufd_access *access);
 int iommufd_access_set_ioas(struct iommufd_access *access, u32 ioas_id);
+bool iommufd_access_ioas_is_attached(struct iommufd_access *access);
 
 void iommufd_ctx_get(struct iommufd_ctx *ictx);
 
-- 
2.39.1