[PATCH v3 4/5] iommufd: Add replace support in iommufd_access_set_ioas()

[Nicolin Chen <nicolinc@nvidia.com>]

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.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 drivers/iommu/iommufd/device.c          | 15 +++++++++++++--
 drivers/iommu/iommufd/iommufd_private.h |  1 +
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index a955ebd4bd5d..c44d6e7a2ed7 100644
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -712,11 +712,22 @@ 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;
+
+	mutex_unlock(&access->ioas_lock);
+	access->ops->unmap(access->data, 0, ULONG_MAX);
+	mutex_lock(&access->ioas_lock);
+
 	if (cur_ioas) {
 		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);
 
@@ -790,11 +801,11 @@ 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 94e88377a7fc..44e77ea9c399 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -311,6 +311,7 @@ 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;
-- 
2.39.2