[Xen-devel] [PATCH] xen/passthrough: Support a single iommu_domain(context bank) 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 occured 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>
---
 xen/drivers/passthrough/arm/smmu.c |  113 ++++++++++++++++++++++++++++--------
 1 file changed, 88 insertions(+), 25 deletions(-)

diff --git a/xen/drivers/passthrough/arm/smmu.c 
b/xen/drivers/passthrough/arm/smmu.c
index a7a7da9..9b46054 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.
         * */
@@ -315,6 +316,26 @@ static struct iommu_group *iommu_group_get(struct device 
*dev)
 
 #define iommu_group_get_iommudata(group) (group)->cfg
 
+static int iommu_domain_add_device(struct iommu_domain *domain,
+                                 struct device *dev)
+{
+       dev_iommu_domain(dev) = domain;
+
+       atomic_inc(&domain->ref);
+
+       return 0;
+}
+
+static int iommu_domain_remove_device(struct iommu_domain *domain,
+                                 struct device *dev)
+{
+       dev_iommu_domain(dev) = NULL;
+
+       atomic_dec(&domain->ref);
+
+       return 0;
+}
+
 /***** Start of Linux SMMU code *****/
 
 /* Maximum number of stream IDs assigned to a single device */
@@ -1583,7 +1604,7 @@ static int arm_smmu_attach_dev(struct iommu_domain 
*domain, struct device *dev)
        ret = arm_smmu_domain_add_master(smmu_domain, cfg);
 
        if (!ret)
-               dev_iommu_domain(dev) = domain;
+               ret = iommu_domain_add_device(domain, dev);
        return ret;
 }
 
@@ -1596,7 +1617,7 @@ static void arm_smmu_detach_dev(struct iommu_domain 
*domain, struct device *dev)
        if (!cfg)
                return;
 
-       dev_iommu_domain(dev) = NULL;
+       iommu_domain_remove_device(domain, dev);
        arm_smmu_domain_remove_master(smmu_domain, cfg);
 }
 
@@ -2569,7 +2590,9 @@ static int arm_smmu_assign_dev(struct domain *d, u8 devfn,
 {
        struct iommu_domain *domain;
        struct arm_smmu_xen_domain *xen_domain;
+       struct arm_smmu_device *smmu;
        int ret;
+       int existing_ctxt_fnd = 0;
 
        xen_domain = domain_hvm_iommu(d)->arch.priv;
 
@@ -2585,29 +2608,65 @@ static int arm_smmu_assign_dev(struct domain *d, u8 
devfn,
                        return ret;
        }
 
-       /*
-        * 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;
+       if (!list_empty(&xen_domain->contexts)) {
+               smmu = find_smmu_for_device(dev);
+               if (!smmu) {
+                       dev_err(dev, "cannot find SMMU\n");
+                       return -ENXIO;
+               }
 
-       ret = arm_smmu_domain_init(domain);
-       if (ret)
-               goto err_dom_init;
+               /* Loop through the &xen_domain->contexts to locate a context 
assigned to this SMMU */
+               spin_lock(&xen_domain->lock);
+               list_for_each_entry(domain, &xen_domain->contexts, list) {
+                       if(domain->priv->smmu == smmu)
+                       {
+                               /* We have found a context already associated 
with the same xen domain and SMMU */
+                               ret = arm_smmu_attach_dev(domain, dev);
+                               if (ret) {
+                                       /* 
+                                        * TODO: If arm_smmu_attach_dev fails, 
should we perform arm_smmu_domain_destroy,
+                                        * eventhough another smmu_master is 
configured correctly? If Not, what error 
+                                        * code should we use
+                                        */
+                                       dev_err(dev, "cannot attach device to 
already existing iommu_domain\n");
+                                       return -ENXIO;
+                               }
+
+                               existing_ctxt_fnd = 1;
+                               break;
+                       }
+                       
+               }
+               spin_unlock(&xen_domain->lock);
+       }
+       
+       if(!existing_ctxt_fnd){
 
-       domain->priv->cfg.domain = d;
+               domain = xzalloc(struct iommu_domain);
+               if (!domain)
+                       return -ENOMEM;
 
-       ret = arm_smmu_attach_dev(domain, dev);
-       if (ret)
-               goto err_attach_dev;
 
-       spin_lock(&xen_domain->lock);
-       /* Chain the new context to the domain */
-       list_add(&domain->list, &xen_domain->contexts);
-       spin_unlock(&xen_domain->lock);
+               ret = arm_smmu_domain_init(domain);
+               if (ret)
+                       goto err_dom_init;
+
+               domain->priv->cfg.domain = d;
+
+               ret = arm_smmu_attach_dev(domain, dev);
+               if (ret)
+                       goto err_attach_dev;
+
+               spin_lock(&xen_domain->lock);
+               /* Chain the new context to the domain */
+               list_add(&domain->list, &xen_domain->contexts);
+               spin_unlock(&xen_domain->lock);
+               
+       }
 
        return 0;
 
@@ -2633,12 +2692,16 @@ static int arm_smmu_deassign_dev(struct domain *d, 
struct device *dev)
 
        arm_smmu_detach_dev(domain, dev);
 
-       spin_lock(&xen_domain->lock);
-       list_del(&domain->list);
-       spin_unlock(&xen_domain->lock);
+       if (domain->ref.counter == 0)
+       {
 
-       arm_smmu_domain_destroy(domain);
-       xfree(domain);
+               spin_lock(&xen_domain->lock);
+               list_del(&domain->list);
+               spin_unlock(&xen_domain->lock);
+
+               arm_smmu_domain_destroy(domain);
+               xfree(domain);
+       }
 
        return 0;
 }
-- 
1.7.9.5


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