linux-kernel - Re: [PATCH] iommu: Implement deferred domain attachment

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Date:   Mon, 18 May 2020 15:26:56 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     iommu@...ts.linux-foundation.org, Tom Murphy <murphyt7@....ie>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu: Implement deferred domain attachment

On Fri, May 15, 2020 at 08:23:13PM +0100, Robin Murphy wrote:
> But that's not what this is; this is (supposed to be) the exact same "don't
> actually perform the attach yet" logic as before, just restricting it to
> default domains in the one place that it actually needs to be, so as not to
> fundamentally bugger up iommu_attach_device() in a way that prevents it from
> working as expected at the correct point later.

You are right, that is better. I tested it and it seems to work. Updated
diff attached, with a minor cleanup included. Mind sending it as a
proper patch I can send upstream?

Thanks,

	Joerg

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 7b375421afba..a9d02bc3ab5b 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -693,6 +693,15 @@ static int iommu_group_create_direct_mappings(struct iommu_group *group,
 	return ret;
 }
 
+static bool iommu_is_attach_deferred(struct iommu_domain *domain,
+				     struct device *dev)
+{
+	if (domain->ops->is_attach_deferred)
+		return domain->ops->is_attach_deferred(domain, dev);
+
+	return false;
+}
+
 /**
  * iommu_group_add_device - add a device to an iommu group
  * @group: the group into which to add the device (reference should be held)
@@ -705,6 +714,7 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
 {
 	int ret, i = 0;
 	struct group_device *device;
+	struct iommu_domain *domain;
 
 	device = kzalloc(sizeof(*device), GFP_KERNEL);
 	if (!device)
@@ -747,7 +757,8 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
 
 	mutex_lock(&group->mutex);
 	list_add_tail(&device->list, &group->devices);
-	if (group->domain)
+	domain = group->domain;
+	if (domain  && !iommu_is_attach_deferred(domain, dev))
 		ret = __iommu_attach_device(group->domain, dev);
 	mutex_unlock(&group->mutex);
 	if (ret)
@@ -1653,9 +1664,6 @@ static int __iommu_attach_device(struct iommu_domain *domain,
 				 struct device *dev)
 {
 	int ret;
-	if ((domain->ops->is_attach_deferred != NULL) &&
-	    domain->ops->is_attach_deferred(domain, dev))
-		return 0;
 
 	if (unlikely(domain->ops->attach_dev == NULL))
 		return -ENODEV;
@@ -1727,8 +1735,7 @@ EXPORT_SYMBOL_GPL(iommu_sva_unbind_gpasid);
 static void __iommu_detach_device(struct iommu_domain *domain,
 				  struct device *dev)
 {
-	if ((domain->ops->is_attach_deferred != NULL) &&
-	    domain->ops->is_attach_deferred(domain, dev))
+	if (iommu_is_attach_deferred(domain, dev))
 		return;
 
 	if (unlikely(domain->ops->detach_dev == NULL))