Re: [PATCH 06/20] iommu/exynos: Implement an IDENTITY domain

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On 2023-05-01 19:02, Jason Gunthorpe wrote:
What exynos calls exynos_iommu_detach_device is actually putting the iommu
into identity mode.

Move to the new core support for ARM_DMA_USE_IOMMU by defining
ops->identity_domain.

Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
  drivers/iommu/exynos-iommu.c | 64 ++++++++++++++++++------------------
  1 file changed, 32 insertions(+), 32 deletions(-)

diff --git a/drivers/iommu/exynos-iommu.c b/drivers/iommu/exynos-iommu.c
index c275fe71c4db32..6ff7901103948a 100644
--- a/drivers/iommu/exynos-iommu.c
+++ b/drivers/iommu/exynos-iommu.c
@@ -24,6 +24,7 @@
typedef u32 sysmmu_iova_t;
  typedef u32 sysmmu_pte_t;
+static struct iommu_domain exynos_identity_domain;
/* We do not consider super section mapping (16MB) */
  #define SECT_ORDER 20
@@ -829,7 +830,7 @@ static int __maybe_unused exynos_sysmmu_suspend(struct device *dev)
  		struct exynos_iommu_owner *owner = dev_iommu_priv_get(master);
mutex_lock(&owner->rpm_lock);
-		if (data->domain) {
+		if (&data->domain->domain != &exynos_identity_domain) {
  			dev_dbg(data->sysmmu, "saving state\n");
  			__sysmmu_disable(data);
  		}
@@ -847,7 +848,7 @@ static int __maybe_unused exynos_sysmmu_resume(struct device *dev)
  		struct exynos_iommu_owner *owner = dev_iommu_priv_get(master);
mutex_lock(&owner->rpm_lock);
-		if (data->domain) {
+		if (&data->domain->domain != &exynos_identity_domain) {
  			dev_dbg(data->sysmmu, "restoring state\n");
  			__sysmmu_enable(data);
  		}
@@ -980,17 +981,22 @@ static void exynos_iommu_domain_free(struct iommu_domain *iommu_domain)
  	kfree(domain);
  }
-static void exynos_iommu_detach_device(struct iommu_domain *iommu_domain,
-				    struct device *dev)
+static int exynos_iommu_identity_attach(struct iommu_domain *identity_domain,
+					struct device *dev)
  {
-	struct exynos_iommu_domain *domain = to_exynos_domain(iommu_domain);
  	struct exynos_iommu_owner *owner = dev_iommu_priv_get(dev);
-	phys_addr_t pagetable = virt_to_phys(domain->pgtable);
+	struct exynos_iommu_domain *domain;
+	phys_addr_t pagetable;
  	struct sysmmu_drvdata *data, *next;
  	unsigned long flags;
- if (!has_sysmmu(dev) || owner->domain != iommu_domain)
-		return;
+	if (!owner)
+		return -ENODEV;

That can't be true - devices can't be attached without having already dereferenced their group, which means they've been through probe_device successfully.

+	if (owner->domain == identity_domain)
+		return 0;
+
+	domain = to_exynos_domain(owner->domain);
+	pagetable = virt_to_phys(domain->pgtable);

Identity domains by definition shouldn't have a pagetable? I don't think virt_to_phys(NULL) can be assumed to be valid or safe in general.

mutex_lock(&owner->rpm_lock); @@ -1009,15 +1015,25 @@ static void exynos_iommu_detach_device(struct iommu_domain *iommu_domain,
  		list_del_init(&data->domain_node);
  		spin_unlock(&data->lock);
  	}

This iterates the whole domain->clients list, which may include other devices from other groups belonging to other IOMMU instances. I think that's technically an issue already given that we support cross-instance domain attach here, which the DRM drivers rely on. I can't quite work out off-hand if this is liable to make it any worse or not :/

-	owner->domain = NULL;
+	owner->domain = identity_domain;
  	spin_unlock_irqrestore(&domain->lock, flags);
mutex_unlock(&owner->rpm_lock); dev_dbg(dev, "%s: Detached IOMMU with pgtable %pa\n", __func__,

This no longer makes much sense.

  		&pagetable);
+	return 0;
  }
+static struct iommu_domain_ops exynos_identity_ops = {
+	.attach_dev = exynos_iommu_identity_attach,
+};
+
+static struct iommu_domain exynos_identity_domain = {
+	.type = IOMMU_DOMAIN_IDENTITY,
+	.ops = &exynos_identity_ops,
+};
+
  static int exynos_iommu_attach_device(struct iommu_domain *iommu_domain,
  				   struct device *dev)
  {
@@ -1026,12 +1042,11 @@ static int exynos_iommu_attach_device(struct iommu_domain *iommu_domain,
  	struct sysmmu_drvdata *data;
  	phys_addr_t pagetable = virt_to_phys(domain->pgtable);
  	unsigned long flags;
+	int err;
- if (!has_sysmmu(dev))
-		return -ENODEV;
-
-	if (owner->domain)
-		exynos_iommu_detach_device(owner->domain, dev);
+	err = exynos_iommu_identity_attach(&exynos_identity_domain, dev);
+	if (err)
+		return err;
mutex_lock(&owner->rpm_lock); @@ -1407,26 +1422,12 @@ static struct iommu_device *exynos_iommu_probe_device(struct device *dev)
  	return &data->iommu;
  }
-static void exynos_iommu_set_platform_dma(struct device *dev)
-{
-	struct exynos_iommu_owner *owner = dev_iommu_priv_get(dev);
-
-	if (owner->domain) {
-		struct iommu_group *group = iommu_group_get(dev);
-
-		if (group) {
-			exynos_iommu_detach_device(owner->domain, dev);
-			iommu_group_put(group);
-		}
-	}
-}
-
  static void exynos_iommu_release_device(struct device *dev)
  {
  	struct exynos_iommu_owner *owner = dev_iommu_priv_get(dev);
  	struct sysmmu_drvdata *data;
- exynos_iommu_set_platform_dma(dev);
+	WARN_ON(exynos_iommu_identity_attach(&exynos_identity_domain, dev));
list_for_each_entry(data, &owner->controllers, owner_node)
  		device_link_del(data->link);
@@ -1457,6 +1458,7 @@ static int exynos_iommu_of_xlate(struct device *dev,
INIT_LIST_HEAD(&owner->controllers);
  		mutex_init(&owner->rpm_lock);
+		owner->domain = &exynos_identity_domain;

I think strictly this would be more of a probe_device thing than an of_xlate thing, but it's not super-important.

Thanks,
Robin.

  		dev_iommu_priv_set(dev, owner);
  	}
@@ -1471,11 +1473,9 @@ static int exynos_iommu_of_xlate(struct device *dev,
  }
static const struct iommu_ops exynos_iommu_ops = {
+	.identity_domain = &exynos_identity_domain,
  	.domain_alloc = exynos_iommu_domain_alloc,
  	.device_group = generic_device_group,
-#ifdef CONFIG_ARM
-	.set_platform_dma_ops = exynos_iommu_set_platform_dma,
-#endif
  	.probe_device = exynos_iommu_probe_device,
  	.release_device = exynos_iommu_release_device,
  	.pgsize_bitmap = SECT_SIZE | LPAGE_SIZE | SPAGE_SIZE,



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