A VMID is generated in an IOMMU driver, being called from this
->attach_group() callback. So call ->get_vmid() right after it
creates a new VMID, and call ->set_vmid() before it, to let it
reuse the same VMID.

Signed-off-by: Nicolin Chen <nicol...@nvidia.com>
---
 drivers/vfio/vfio.c  | 12 ++++++++++++
 include/linux/vfio.h |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index c17b25c127a2..8b7442deca93 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -1080,9 +1080,21 @@ static int __vfio_container_attach_groups(struct 
vfio_container *container,
        int ret = -ENODEV;
 
        list_for_each_entry(group, &container->group_list, container_next) {
+               if (driver->ops->set_vmid && container->vmid != 
VFIO_IOMMU_VMID_INVALID) {
+                       ret = driver->ops->set_vmid(data, container->vmid);
+                       if (ret)
+                               goto unwind;
+               }
+
                ret = driver->ops->attach_group(data, group->iommu_group);
                if (ret)
                        goto unwind;
+
+               if (driver->ops->get_vmid && container->vmid == 
VFIO_IOMMU_VMID_INVALID) {
+                       ret = driver->ops->get_vmid(data, &container->vmid);
+                       if (ret)
+                               goto unwind;
+               }
        }
 
        return ret;
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index b53a9557884a..b43e7cbef4ab 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -126,6 +126,8 @@ struct vfio_iommu_driver_ops {
                                                   struct iommu_group *group);
        void            (*notify)(void *iommu_data,
                                  enum vfio_iommu_notify_type event);
+       int             (*set_vmid)(void *iommu_data, u32 vmid);
+       int             (*get_vmid)(void *iommu_data, u32 *vmid);
 };
 
 extern int vfio_register_iommu_driver(const struct vfio_iommu_driver_ops *ops);
-- 
2.17.1

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