[PATCH v5 p2 09/19] xen/passthrough: iommu_deassign_device_dt: By default reassign device to nobody

[Julien Grall <julien.grall@citrix.com>]

From: Julien Grall <julien.grall@linaro.org>

Currently, when the device is deassigned from a domain, we directly reassign
to DOM0.

As the device may not have been correctly reset, this may lead to corruption or
expose some part of DOM0 memory. Also, we may have no way to reset some
platform devices.

If Xen reassigns the device to "nobody", it may receive some global/context
fault because the transaction has failed (indeed the context has been
marked invalid). Unfortunately there is no simple way to quiesce a buggy
hardware. I think we could live with that for a first version of platform
device passthrough.

DOM0 will have to issue an hypercall to assign the device to itself if it
wants to use it.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Stefano Stabellini <stefano.stabellini@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

---
    Note: This behavior is documented in a following patch which extend
    DOMCT_*assign_device to support non-PCI passthrough.

    Changes in v5:
        - Add Ian's ack

    Changes in v4:
        - Add Stefano's ack

    Changes in v3:
        - Use the coding style of the new SMMU drivers

    Changes in v2:
        - Fix typoes in the commit message
        - Update commit message
---
 xen/drivers/passthrough/arm/smmu.c    | 8 +++++++-
 xen/drivers/passthrough/device_tree.c | 9 +++------
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/xen/drivers/passthrough/arm/smmu.c b/xen/drivers/passthrough/arm/smmu.c
index 8a9b58b..65de50b 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -2692,7 +2692,7 @@ static int arm_smmu_reassign_dev(struct domain *s, struct domain *t,
 	int ret = 0;
 
 	/* Don't allow remapping on other domain than hwdom */
-	if (t != hardware_domain)
+	if (t && t != hardware_domain)
 		return -EPERM;
 
 	if (t == s)
@@ -2702,6 +2702,12 @@ static int arm_smmu_reassign_dev(struct domain *s, struct domain *t,
 	if (ret)
 		return ret;
 
+	if (t) {
+		ret = arm_smmu_assign_dev(t, devfn, dev);
+		if (ret)
+			return ret;
+	}
+
 	return 0;
 }
 
diff --git a/xen/drivers/passthrough/device_tree.c b/xen/drivers/passthrough/device_tree.c
index 05ab274..0ec4103 100644
--- a/xen/drivers/passthrough/device_tree.c
+++ b/xen/drivers/passthrough/device_tree.c
@@ -80,15 +80,12 @@ int iommu_deassign_dt_device(struct domain *d, struct dt_device_node *dev)
 
     spin_lock(&dtdevs_lock);
 
-    rc = hd->platform_ops->reassign_device(d, hardware_domain,
-                                           0, dt_to_dev(dev));
+    rc = hd->platform_ops->reassign_device(d, NULL, 0, dt_to_dev(dev));
     if ( rc )
         goto fail;
 
-    list_del(&dev->domain_list);
-
-    dt_device_set_used_by(dev, hardware_domain->domain_id);
-    list_add(&dev->domain_list, &domain_hvm_iommu(hardware_domain)->dt_devices);
+    list_del_init(&dev->domain_list);
+    dt_device_set_used_by(dev, DOMID_IO);
 
 fail:
     spin_unlock(&dtdevs_lock);
-- 
2.1.4