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Date:   Fri, 27 Jan 2023 18:29:42 -0800
From:   Nicolin Chen <nicolinc@...dia.com>
To:     <jgg@...dia.com>, <kevin.tian@...el.com>
CC:     <yi.l.liu@...el.com>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/3] iommufd/device: Change iommufd_hw_pagetable_has_group to device centric

The iommufd_hw_pagetable_has_group() is a little hack to check whether
a hw_pagetable has an idev->group attached. This isn't device-centric
firstly, but also requires the hw_pagetable to maintain a device list
with a devices_lock, which gets overcomplicated among the routines for
different use cases, upcoming nested hwpts especially.

Since we can compare the iommu_group->domain and the hwpt->domain to
serve the same purpose while being device centric, change it and drop
the device list with the devices_lock accordingly.

Note that, in the detach routine, it previously checked !has_group as
there was a list_del on the device list. But now, the device is still
being attached to the hwpt, so the if logic gets inverted.

Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
---
 drivers/iommu/iommufd/device.c          | 40 ++++++++-----------------
 drivers/iommu/iommufd/hw_pagetable.c    |  5 ----
 drivers/iommu/iommufd/iommufd_private.h |  2 --
 3 files changed, 12 insertions(+), 35 deletions(-)

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index 0248073e3169..5a5dfc0c4ca0 100644
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -24,8 +24,6 @@ struct iommufd_device {
 	struct iommufd_object obj;
 	struct iommufd_ctx *ictx;
 	struct iommufd_hw_pagetable *hwpt;
-	/* Head at iommufd_hw_pagetable::devices */
-	struct list_head devices_item;
 	/* always the physical device */
 	struct device *dev;
 	struct iommu_group *group;
@@ -181,15 +179,15 @@ static int iommufd_device_setup_msi(struct iommufd_device *idev,
 	return 0;
 }
 
-static bool iommufd_hw_pagetable_has_group(struct iommufd_hw_pagetable *hwpt,
-					   struct iommu_group *group)
+static bool iommufd_hw_pagetable_has_device(struct iommufd_hw_pagetable *hwpt,
+					    struct device *dev)
 {
-	struct iommufd_device *cur_dev;
-
-	list_for_each_entry(cur_dev, &hwpt->devices, devices_item)
-		if (cur_dev->group == group)
-			return true;
-	return false;
+	/*
+	 * iommu_get_domain_for_dev() returns an iommu_group->domain ptr, if it
+	 * is the same domain as the hwpt->domain, it means that this hwpt has
+	 * the iommu_group/device.
+	 */
+	return hwpt->domain == iommu_get_domain_for_dev(dev);
 }
 
 static int iommufd_device_do_attach(struct iommufd_device *idev,
@@ -200,8 +198,6 @@ static int iommufd_device_do_attach(struct iommufd_device *idev,
 
 	lockdep_assert_held(&hwpt->ioas->mutex);
 
-	mutex_lock(&hwpt->devices_lock);
-
 	/*
 	 * Try to upgrade the domain we have, it is an iommu driver bug to
 	 * report IOMMU_CAP_ENFORCE_CACHE_COHERENCY but fail
@@ -215,25 +211,20 @@ static int iommufd_device_do_attach(struct iommufd_device *idev,
 					hwpt->domain);
 		if (!hwpt->enforce_cache_coherency) {
 			WARN_ON(refcount_read(hwpt->devices_users) == 1);
-			rc = -EINVAL;
-			goto out_unlock;
+			return -EINVAL;
 		}
 	}
 
 	rc = iopt_table_enforce_group_resv_regions(&hwpt->ioas->iopt, idev->dev,
 						   idev->group, &sw_msi_start);
 	if (rc)
-		goto out_unlock;
+		return rc;
 
 	rc = iommufd_device_setup_msi(idev, hwpt, sw_msi_start);
 	if (rc)
 		goto out_iova;
 
-	/*
-	 * FIXME: Hack around missing a device-centric iommu api, only attach to
-	 * the group once for the first device that is in the group.
-	 */
-	if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {
+	if (!iommufd_hw_pagetable_has_device(hwpt, idev->dev)) {
 		rc = iommu_attach_group(hwpt->domain, idev->group);
 		if (rc)
 			goto out_iova;
@@ -250,16 +241,12 @@ static int iommufd_device_do_attach(struct iommufd_device *idev,
 	idev->hwpt = hwpt;
 	refcount_inc(&hwpt->obj.users);
 	refcount_inc(hwpt->devices_users);
-	list_add(&idev->devices_item, &hwpt->devices);
-	mutex_unlock(&hwpt->devices_lock);
 	return 0;
 
 out_detach:
 	iommu_detach_group(hwpt->domain, idev->group);
 out_iova:
 	iopt_remove_reserved_iova(&hwpt->ioas->iopt, idev->dev);
-out_unlock:
-	mutex_unlock(&hwpt->devices_lock);
 	return rc;
 }
 
@@ -385,10 +372,8 @@ 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);
 	refcount_dec(hwpt->devices_users);
-	list_del(&idev->devices_item);
-	if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {
+	if (iommufd_hw_pagetable_has_device(hwpt, idev->dev)) {
 		if (refcount_read(hwpt->devices_users) == 1) {
 			iopt_table_remove_domain(&hwpt->ioas->iopt,
 						 hwpt->domain);
@@ -397,7 +382,6 @@ void iommufd_device_detach(struct iommufd_device *idev)
 		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)
diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
index 910e759ffeac..868a126ff37d 100644
--- a/drivers/iommu/iommufd/hw_pagetable.c
+++ b/drivers/iommu/iommufd/hw_pagetable.c
@@ -11,11 +11,8 @@ void iommufd_hw_pagetable_destroy(struct iommufd_object *obj)
 	struct iommufd_hw_pagetable *hwpt =
 		container_of(obj, struct iommufd_hw_pagetable, obj);
 
-	WARN_ON(!list_empty(&hwpt->devices));
-
 	iommu_domain_free(hwpt->domain);
 	refcount_dec(&hwpt->ioas->obj.users);
-	mutex_destroy(&hwpt->devices_lock);
 	WARN_ON(!refcount_dec_if_one(hwpt->devices_users));
 	kfree(hwpt->devices_users);
 }
@@ -45,9 +42,7 @@ iommufd_hw_pagetable_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
 		goto out_abort;
 	}
 
-	INIT_LIST_HEAD(&hwpt->devices);
 	INIT_LIST_HEAD(&hwpt->hwpt_item);
-	mutex_init(&hwpt->devices_lock);
 	hwpt->devices_users = kzalloc(sizeof(*hwpt->devices_users), GFP_KERNEL);
 	if (!hwpt->devices_users) {
 		rc = -ENOMEM;
diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
index f128d77fb076..1c8e59b37f46 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -246,9 +246,7 @@ struct iommufd_hw_pagetable {
 	bool msi_cookie : 1;
 	/* Head at iommufd_ioas::hwpt_list */
 	struct list_head hwpt_item;
-	struct mutex devices_lock;
 	refcount_t *devices_users;
-	struct list_head devices;
 };
 
 struct iommufd_hw_pagetable *
-- 
2.39.1

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