[PATCH v1 7/8] iommufd/device: Use iommu_group_replace_domain()

[Nicolin Chen <nicolinc@xxxxxxxxxx>]

iommu_group_replace_domain() is introduced to support use cases where an
iommu_group can be attached to a new domain without getting detached from
the old one. This replacement feature will be useful, for cases such as:
1) vPASID mode, when a guest wants to replace a single pasid (PASID=0)
   table with a larger table (PASID=N)
2) Nesting mode, when switching the attaching device from an S2 domain
   to an S1 domain, or when switching between relevant S1 domains.
as it allows these cases to switch seamlessly without a DMA disruption.

So, call iommu_group_replace_domain() in the iommufd_device_do_attach().
And then decrease the refcount of the hwpt being replaced.

Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
---
 drivers/iommu/iommufd/device.c          | 26 +++++++++++++++++++++++--
 drivers/iommu/iommufd/iommufd_private.h |  2 ++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index 8118d5262800..c7701e449f3d 100644
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -9,6 +9,8 @@
 #include "io_pagetable.h"
 #include "iommufd_private.h"
 
+MODULE_IMPORT_NS(IOMMUFD_INTERNAL);
+
 static bool allow_unsafe_interrupts;
 module_param(allow_unsafe_interrupts, bool, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(
@@ -197,6 +199,7 @@ static bool iommufd_hw_pagetable_has_group(struct iommufd_hw_pagetable *hwpt,
 static int iommufd_device_do_attach(struct iommufd_device *idev,
 				    struct iommufd_hw_pagetable *hwpt)
 {
+	struct iommufd_hw_pagetable *cur_hwpt = idev->hwpt;
 	phys_addr_t sw_msi_start = PHYS_ADDR_MAX;
 	int rc;
 
@@ -234,7 +237,7 @@ static int iommufd_device_do_attach(struct iommufd_device *idev,
 	 * the group once for the first device that is in the group.
 	 */
 	if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {
-		rc = iommu_attach_group(hwpt->domain, idev->group);
+		rc = iommu_group_replace_domain(idev->group, hwpt->domain);
 		if (rc)
 			goto out_iova;
 
@@ -246,6 +249,18 @@ static int iommufd_device_do_attach(struct iommufd_device *idev,
 		}
 	}
 
+	if (cur_hwpt) {
+		/* Replace the cur_hwpt */
+		mutex_lock(&cur_hwpt->devices_lock);
+		if (cur_hwpt->ioas != hwpt->ioas)
+			iopt_remove_reserved_iova(&cur_hwpt->ioas->iopt,
+						  idev->dev);
+		list_del(&cur_hwpt->hwpt_item);
+		list_del(&idev->devices_item);
+		refcount_dec(&cur_hwpt->obj.users);
+		refcount_dec(&idev->obj.users);
+		mutex_unlock(&cur_hwpt->devices_lock);
+	}
 	idev->hwpt = hwpt;
 	refcount_inc(&hwpt->obj.users);
 	list_add(&idev->devices_item, &hwpt->devices);
@@ -253,7 +268,10 @@ static int iommufd_device_do_attach(struct iommufd_device *idev,
 	return 0;
 
 out_detach:
-	iommu_detach_group(hwpt->domain, idev->group);
+	if (cur_hwpt)
+		iommu_group_replace_domain(idev->group, cur_hwpt->domain);
+	else
+		iommu_detach_group(hwpt->domain, idev->group);
 out_iova:
 	iopt_remove_reserved_iova(&hwpt->ioas->iopt, idev->dev);
 out_unlock:
@@ -343,6 +361,9 @@ int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id)
 		struct iommufd_hw_pagetable *hwpt =
 			container_of(pt_obj, struct iommufd_hw_pagetable, obj);
 
+		if (idev->hwpt == hwpt)
+			goto out_done;
+
 		rc = iommufd_device_do_attach(idev, hwpt);
 		if (rc)
 			goto out_put_pt_obj;
@@ -367,6 +388,7 @@ int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id)
 	}
 
 	refcount_inc(&idev->obj.users);
+out_done:
 	*pt_id = idev->hwpt->obj.id;
 	rc = 0;
 
diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index 593138bb37b8..200c783800ad 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -9,6 +9,8 @@
 #include <linux/refcount.h>
 #include <linux/uaccess.h>
 
+#include "../iommu-priv.h"
+
 struct iommu_domain;
 struct iommu_group;
 struct iommu_option;
-- 
2.39.1