[PATCH v2 08/10] iommufd/device: Use iommu_group_replace_domain()

[Nicolin Chen <nicolinc@nvidia.com>]

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 add a __iommmufd_device_detach helper to allow the replace routine to
do a partial detach on the current hwpt that's being replaced. Though the
updated locking logic is overcomplicated, it will be eased, once those
iopt_table_add/remove_ioas and list_add/del calls are moved to hwpt's
allocation/destroy() functions in the coming nesting series, as that'll
depend on a new ->domain_alloc_user op in the iommu core.

Also, block replace operations that are from/to auto_domains, i.e. only
user-allocated hw_pagetables can be replaced or replaced with.

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 drivers/iommu/iommufd/device.c          | 101 +++++++++++++++++-------
 drivers/iommu/iommufd/iommufd_private.h |   2 +
 2 files changed, 76 insertions(+), 27 deletions(-)

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index b8c3e3baccb5..8a9834fc129a 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(
@@ -194,9 +196,61 @@ static bool iommufd_hw_pagetable_has_group(struct iommufd_hw_pagetable *hwpt,
 	return false;
 }
 
+/**
+ * __iommmufd_device_detach - Detach a device from idev->hwpt to new_hwpt
+ * @idev: device to detach
+ * @new_hwpt: new hw_pagetable to attach (pass in NULL for a simple detach)
+ * @detach_group: flag to call iommu_detach_group
+ *
+ * This is a cleanup helper shared by the replace and detach routines. Comparing
+ * to a detach routine, a replace routine only needs a partial detach procedure:
+ * it does not need the iommu_detach_group(); it will attach the device to a new
+ * hw_pagetable after a partial detach from the currently attached hw_pagetable,
+ * so certain steps can be skipped if two hw_pagetables have the same IOAS.
+ */
+static void __iommmufd_device_detach(struct iommufd_device *idev,
+				     struct iommufd_hw_pagetable *new_hwpt,
+				     bool detach_group)
+{
+	struct iommufd_hw_pagetable *hwpt = idev->hwpt;
+	struct iommufd_ioas *new_ioas = NULL;
+
+	if (new_hwpt)
+		new_ioas = new_hwpt->ioas;
+
+	mutex_lock(&hwpt->devices_lock);
+	list_del(&idev->devices_item);
+	if (hwpt->ioas != new_ioas)
+		mutex_lock(&hwpt->ioas->mutex);
+	if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {
+		if (list_empty(&hwpt->devices)) {
+			iopt_table_remove_domain(&hwpt->ioas->iopt,
+						 hwpt->domain);
+			list_del(&hwpt->hwpt_item);
+		}
+		if (detach_group)
+			iommu_detach_group(hwpt->domain, idev->group);
+	}
+	if (hwpt->ioas != new_ioas) {
+		iopt_remove_reserved_iova(&hwpt->ioas->iopt, idev->dev);
+		mutex_unlock(&hwpt->ioas->mutex);
+	}
+	mutex_unlock(&hwpt->devices_lock);
+
+	if (hwpt->auto_domain)
+		iommufd_object_destroy_user(idev->ictx, &hwpt->obj);
+	else
+		refcount_dec(&hwpt->obj.users);
+
+	idev->hwpt = NULL;
+
+	refcount_dec(&idev->obj.users);
+}
+
 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;
 
@@ -236,7 +290,7 @@ 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;
 
@@ -249,6 +303,10 @@ static int iommufd_device_do_attach(struct iommufd_device *idev,
 		}
 	}
 
+	/* Replace the cur_hwpt without iommu_detach_group() */
+	if (cur_hwpt)
+		__iommmufd_device_detach(idev, hwpt, false);
+
 	idev->hwpt = hwpt;
 	refcount_inc(&hwpt->obj.users);
 	list_add(&idev->devices_item, &hwpt->devices);
@@ -256,7 +314,10 @@ 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:
@@ -345,6 +406,13 @@ 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;
+		if (idev->hwpt && idev->hwpt->auto_domain) {
+			rc = -EBUSY;
+			goto out_put_pt_obj;
+		}
+
 		mutex_lock(&hwpt->ioas->mutex);
 		rc = iommufd_device_do_attach(idev, hwpt);
 		mutex_unlock(&hwpt->ioas->mutex);
@@ -356,6 +424,8 @@ int iommufd_device_attach(struct iommufd_device *idev, u32 *pt_id)
 		struct iommufd_ioas *ioas =
 			container_of(pt_obj, struct iommufd_ioas, obj);
 
+		if (idev->hwpt)
+			return -EBUSY;
 		rc = iommufd_device_auto_get_domain(idev, ioas);
 		if (rc)
 			goto out_put_pt_obj;
@@ -367,6 +437,7 @@ 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;
 
@@ -385,31 +456,7 @@ EXPORT_SYMBOL_NS_GPL(iommufd_device_attach, IOMMUFD);
  */
 void iommufd_device_detach(struct iommufd_device *idev)
 {
-	struct iommufd_hw_pagetable *hwpt = idev->hwpt;
-
-	mutex_lock(&hwpt->ioas->mutex);
-	mutex_lock(&hwpt->devices_lock);
-	list_del(&idev->devices_item);
-	if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {
-		if (list_empty(&hwpt->devices)) {
-			iopt_table_remove_domain(&hwpt->ioas->iopt,
-						 hwpt->domain);
-			list_del(&hwpt->hwpt_item);
-		}
-		iommu_detach_group(hwpt->domain, idev->group);
-	}
-	iopt_remove_reserved_iova(&hwpt->ioas->iopt, idev->dev);
-	mutex_unlock(&hwpt->devices_lock);
-	mutex_unlock(&hwpt->ioas->mutex);
-
-	if (hwpt->auto_domain)
-		iommufd_object_destroy_user(idev->ictx, &hwpt->obj);
-	else
-		refcount_dec(&hwpt->obj.users);
-
-	idev->hwpt = NULL;
-
-	refcount_dec(&idev->obj.users);
+	__iommmufd_device_detach(idev, NULL, true);
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_device_detach, IOMMUFD);
 
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