[PATCH 08/14] iommu: Introduce a new iommu_group_replace_domain() API

Jason Gunthorpe
2023-02-25T00:28:15Z

From: Nicolin Chen <nicolinc@nvidia.com>

qemu has a need to replace the translations associated with a domain
when the guest does large-scale operations like switching between an
IDENTITY domain and, say, dma-iommu.c.

Currently, it does this by replacing all the mappings in a single
domain, but this is very inefficient and means that domains have to be
per-device rather than per-translation.

Provide a high-level API to allow replacements of one domain with
another. This is similar to a detach/attach cycle except it doesn't
force the group to go to the blocking domain in-between.

By removing this forced blocking domain the iommu driver has the
opportunity to implement a non-disruptive replacement of the domain to the
greatest extent its hardware allows. This allows the qemu emulation of the
vIOMMU to be more complete, as real hardware often has a non-distruptive
replacement capability.

It could be possible to adderss this by simply removing the protection
from the iommu_attach_group(), but it is not so clear if that is safe for
the few users. Thus, add a new API to serve this new purpose.

All drivers are already required to support changing between active
UNMANAGED domains when using their attach_dev ops.

This API is expected to be used only by IOMMUFD, so add to the iommu-priv
header and mark it as IOMMUFD_INTERNAL.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/iommu/iommu-priv.h | 10 ++++++++++
drivers/iommu/iommu.c | 30 ++++++++++++++++++++++++++++++
2 files changed, 40 insertions(+)
create mode 100644 drivers/iommu/iommu-priv.h

diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
new file mode 100644
index 00000000000000..7c8011bfd15374
--- /dev/null
+++ b/drivers/iommu/iommu-priv.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __LINUX_IOMMU_PRIV_H
+#define __LINUX_IOMMU_PRIV_H
+
+#include <linux/iommu.h>
+
+int iommu_group_replace_domain(struct iommu_group *group,
+ struct iommu_domain *new_domain);
+
+#endif /* __LINUX_IOMMU_PRIV_H */
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 10db680acaed5a..4c91d9bdd114ab 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -33,6 +33,7 @@
#include <linux/msi.h>

#include "dma-iommu.h"
+#include "iommu-priv.h"

#include "iommu-sva.h"

@@ -2191,6 +2192,35 @@ int iommu_attach_group(struct iommu_domain *domain, struct iommu_group *group)
}
EXPORT_SYMBOL_GPL(iommu_attach_group);

+/**
+ * iommu_group_replace_domain - replace the domain that a group is attached to
+ * @new_domain: new IOMMU domain to replace with
+ * @group: IOMMU group that will be attached to the new domain
+ *
+ * This API allows the group to switch domains without being forced to go to
+ * the blocking domain in-between.
+ *
+ * If the currently attached domain is a core domain (e.g. a default_domain),
+ * it will act just like the iommu_attach_group().
+ */
+int iommu_group_replace_domain(struct iommu_group *group,
+ struct iommu_domain *new_domain)
+{
+ int ret;
+
+ if (!new_domain)
+ return -EINVAL;
+
+ mutex_lock(&group->mutex);
+ ret = __iommu_group_set_domain(group, new_domain);
+ if (ret)
+ __iommu_group_for_each_dev(group, group->domain,
+ iommu_group_do_attach_device);
+ mutex_unlock(&group->mutex);
+ return ret;
+}
+EXPORT_SYMBOL_NS_GPL(iommu_group_replace_domain, IOMMUFD_INTERNAL);
+
static int iommu_group_do_set_platform_dma(struct device *dev, void *data)
{
const struct iommu_ops *ops = dev_iommu_ops(dev);
--
2.39.1