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Re: [Xen-devel] [PATCH V2 6/6] iommu/arm: Add Renesas IPMMU-VMSA support

On 14.08.19 20:38, Julien Grall wrote:
Hi Oleksandr,

Hi Julien.

On 02/08/2019 17:39, Oleksandr Tyshchenko wrote:
+static int ipmmu_iommu_domain_init(struct domain *d)
+    struct ipmmu_vmsa_xen_domain *xen_domain;
+    xen_domain = xzalloc(struct ipmmu_vmsa_xen_domain);
+    if ( !xen_domain )
+        return -ENOMEM;
+    spin_lock_init(&xen_domain->lock);
+    INIT_LIST_HEAD(&xen_domain->cache_domains);
+    /*
+     * We don't create Root IPMMU domain here, it will be created on demand +     * only, when attaching the first master device to this Xen domain in
+     * ipmmu_assign_device().
+     * xen_domain->root_domain = NULL;
+    */
+    dom_iommu(d)->arch.priv = xen_domain;

While looking at other part of Xen I realized you don't set IOMMU_FEAT_COHERENT_WALK. Does it mean the IOMMU walker does not support coherent walk (i.e snooping the cache)?

*AFAIK*, not supported.

Linux driver reports coherent_walk is not supported as well.

Note that when this feature is not set, the p2m code will require to clean each P2M entry when updated. So if the IPMMU supports coherent walk, I would strongly suggest to set the flag :).

When playing with non-shared IOMMU in Xen (two years ago), I noticed that I had forgotten to use clean_dcache after updating a page table entry. I could face faults when shattering superpages for example. Once I added it, the faults went away completely.

So, leave IOMMU_FEAT_COHERENT_WALK in disabled state, but will keep your suggestion in mind.



Oleksandr Tyshchenko

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