[Xen-devel] [PATCH v4] xen/passthrough: Support a single iommu_domain per xen domain per SMMU

[Robbie VanVossen <robert.vanvossen@xxxxxxxxxxxxxxx>]

If multiple devices are being passed through to the same domain and they
share a single SMMU, then they only require a single iommu_domain.

In arm_smmu_assign_dev, before a new iommu_domain is created, the
xen_domain->contexts is checked for any iommu_domains that are already
assigned to device that uses the same SMMU as the current device. If one
is found, attach the device to that iommu_domain. If a new one isn't
found, create a new iommu_domain just like before.

The arm_smmu_deassign_dev function assumes that there is a single
device per iommu_domain. This meant that when the first device was
deassigned, the iommu_domain was freed and when another device was
deassigned a crash occurred in xen.

To fix this, a reference counter was added to the iommu_domain struct.
When an arm_smmu_xen_device references an iommu_domain, the
iommu_domains ref is incremented. When that reference is removed, the
iommu_domains ref is decremented. The iommu_domain will only be freed
when the ref is 0.

Signed-off-by: Robbie VanVossen <robert.vanvossen@xxxxxxxxxxxxxxx>
Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>
---
Changed since v3:
  * Fixed formatting
Changed since v2:
  * Fixed coding style
  * Removed an unnecessary error message
  * Added some helper functions to clean up the workflow in arm_smmu_assign_dev 
a bit
Changed since v1:
  * Fixed coding style for comments
  * Move increment/decrement outside of attach/detach functions
  * Expanded xen_domain->lock to protect more of the assign/deassign
    functions
  * Removed iommu_domain add/remove_device functions
---
 xen/drivers/passthrough/arm/smmu.c |   99 ++++++++++++++++++++++++++----------
 1 file changed, 71 insertions(+), 28 deletions(-)

diff --git a/xen/drivers/passthrough/arm/smmu.c 
b/xen/drivers/passthrough/arm/smmu.c
index a7a7da9..8a9b58b 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -223,6 +223,7 @@ struct iommu_domain
        /* Runtime SMMU configuration for this iommu_domain */
        struct arm_smmu_domain          *priv;
 
+       atomic_t ref;
        /* Used to link iommu_domain contexts for a same domain.
         * There is at least one per-SMMU to used by the domain.
         * */
@@ -2564,12 +2565,45 @@ static void arm_smmu_iotlb_flush(struct domain *d, 
unsigned long gfn,
     arm_smmu_iotlb_flush_all(d);
 }
 
+static struct iommu_domain *arm_smmu_get_domain(struct domain *d,
+                                               struct device *dev)
+{
+       struct iommu_domain *domain;
+       struct arm_smmu_xen_domain *xen_domain;
+       struct arm_smmu_device *smmu;
+
+       xen_domain = domain_hvm_iommu(d)->arch.priv;
+
+       smmu = find_smmu_for_device(dev);
+       if (!smmu)
+               return NULL;
+
+       /*
+        * Loop through the &xen_domain->contexts to locate a context
+        * assigned to this SMMU
+        */
+       list_for_each_entry(domain, &xen_domain->contexts, list) {
+               if (domain->priv->smmu == smmu)
+                       return domain;
+       }
+
+       return NULL;
+
+}
+
+static void arm_smmu_destroy_iommu_domain(struct iommu_domain *domain)
+{
+       list_del(&domain->list);
+       arm_smmu_domain_destroy(domain);
+       xfree(domain);
+}
+
 static int arm_smmu_assign_dev(struct domain *d, u8 devfn,
                               struct device *dev)
 {
        struct iommu_domain *domain;
        struct arm_smmu_xen_domain *xen_domain;
-       int ret;
+       int ret = 0;
 
        xen_domain = domain_hvm_iommu(d)->arch.priv;
 
@@ -2585,36 +2619,44 @@ static int arm_smmu_assign_dev(struct domain *d, u8 
devfn,
                        return ret;
        }
 
+       spin_lock(&xen_domain->lock);
+
        /*
-        * TODO: Share the context bank (i.e iommu_domain) when the device is
-        * under the same SMMU as another device assigned to this domain.
-        * Would it useful for PCI
+        * Check to see if a context bank (iommu_domain) already exists for
+        * this xen domain under the same SMMU
         */
-       domain = xzalloc(struct iommu_domain);
-       if (!domain)
-               return -ENOMEM;
+       domain = arm_smmu_get_domain(d, dev);
+       if (!domain) {
 
-       ret = arm_smmu_domain_init(domain);
-       if (ret)
-               goto err_dom_init;
+               domain = xzalloc(struct iommu_domain);
+               if (!domain) {
+                       ret = -ENOMEM;
+                       goto out;
+               }
 
-       domain->priv->cfg.domain = d;
+               ret = arm_smmu_domain_init(domain);
+               if (ret) {
+                       xfree(domain);
+                       goto out;
+               }
 
-       ret = arm_smmu_attach_dev(domain, dev);
-       if (ret)
-               goto err_attach_dev;
+               domain->priv->cfg.domain = d;
 
-       spin_lock(&xen_domain->lock);
-       /* Chain the new context to the domain */
-       list_add(&domain->list, &xen_domain->contexts);
-       spin_unlock(&xen_domain->lock);
+               /* Chain the new context to the domain */
+               list_add(&domain->list, &xen_domain->contexts);
 
-       return 0;
+       }
 
-err_attach_dev:
-       arm_smmu_domain_destroy(domain);
-err_dom_init:
-       xfree(domain);
+       ret = arm_smmu_attach_dev(domain, dev);
+       if (ret) {
+               if (domain->ref.counter == 0)
+                       arm_smmu_destroy_iommu_domain(domain);
+       } else {
+               atomic_inc(&domain->ref);
+       }
+
+out:
+       spin_unlock(&xen_domain->lock);
 
        return ret;
 }
@@ -2631,14 +2673,15 @@ static int arm_smmu_deassign_dev(struct domain *d, 
struct device *dev)
                return -ESRCH;
        }
 
+       spin_lock(&xen_domain->lock);
+
        arm_smmu_detach_dev(domain, dev);
+       atomic_dec(&domain->ref);
 
-       spin_lock(&xen_domain->lock);
-       list_del(&domain->list);
-       spin_unlock(&xen_domain->lock);
+       if (domain->ref.counter == 0)
+               arm_smmu_destroy_iommu_domain(domain);
 
-       arm_smmu_domain_destroy(domain);
-       xfree(domain);
+       spin_unlock(&xen_domain->lock);
 
        return 0;
 }
-- 
1.7.9.5


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