Hi Eric,

On 2020/11/18 19:21, Eric Auger wrote:

On ARM, MSI are translated by the SMMU. An IOVA is allocated
for each MSI doorbell. If both the host and the guest are exposed
with SMMUs, we end up with 2 different IOVAs allocated by each.
guest allocates an IOVA (gIOVA) to map onto the guest MSI
doorbell (gDB). The Host allocates another IOVA (hIOVA) to map
onto the physical doorbell (hDB).

So we end up with 2 untied mappings:
         S1            S2
gIOVA    ->    gDB
              hIOVA    ->    hDB

Currently the PCI device is programmed by the host with hIOVA
as MSI doorbell. So this does not work.

This patch introduces an API to pass gIOVA/gDB to the host so
that gIOVA can be reused by the host instead of re-allocating
a new IOVA. So the goal is to create the following nested mapping:

Does the gDB can be reused under non-nested mode?

         S1            S2
gIOVA    ->    gDB     ->    hDB

and program the PCI device with gIOVA MSI doorbell.

In case we have several devices attached to this nested domain
(devices belonging to the same group), they cannot be isolated
on guest side either. So they should also end up in the same domain
on guest side. We will enforce that all the devices attached to
the host iommu domain use the same physical doorbell and similarly
a single virtual doorbell mapping gets registered (1 single
virtual doorbell is used on guest as well).

[...]

+ *
+ * The associated IOVA can be reused by the host to create a nested
+ * stage2 binding mapping translating into the physical doorbell used
+ * by the devices attached to the domain.
+ *
+ * All devices within the domain must share the same physical doorbell.
+ * A single MSI GIOVA/GPA mapping can be attached to an iommu_domain.
+ */
+
+int iommu_bind_guest_msi(struct iommu_domain *domain,
+			 dma_addr_t giova, phys_addr_t gpa, size_t size)
+{
+	if (unlikely(!domain->ops->bind_guest_msi))
+		return -ENODEV;
+
+	return domain->ops->bind_guest_msi(domain, giova, gpa, size);
+}
+EXPORT_SYMBOL_GPL(iommu_bind_guest_msi);
+
+void iommu_unbind_guest_msi(struct iommu_domain *domain,
+			    dma_addr_t iova)

nit: s/iova/giova

+{
+	if (unlikely(!domain->ops->unbind_guest_msi))
+		return;
+
+	domain->ops->unbind_guest_msi(domain, iova);
+}
+EXPORT_SYMBOL_GPL(iommu_unbind_guest_msi);
+

[...]

Thanks,
Keqian