[PATCH V2] libxl/arm: Create specific IOMMU node to be referred by virtio-mmio device

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Reuse generic IOMMU device tree bindings to communicate Xen specific
information for the virtio devices for which the restricted memory
access using Xen grant mappings need to be enabled.

Insert "iommus" property pointed to the IOMMU node with "xen,grant-dma"
compatible to all virtio devices which backends are going to run in
non-hardware domains (which are non-trusted by default).

Based on device-tree binding from Linux:
Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml

The example of generated nodes:

xen_iommu {
    compatible = "xen,grant-dma";
    #iommu-cells = <0x01>;
    phandle = <0xfde9>;
};

virtio@2000000 {
    compatible = "virtio,mmio";
    reg = <0x00 0x2000000 0x00 0x200>;
    interrupts = <0x00 0x01 0xf01>;
    interrupt-parent = <0xfde8>;
    dma-coherent;
    iommus = <0xfde9 0x01>;
};

virtio@2000200 {
    compatible = "virtio,mmio";
    reg = <0x00 0x2000200 0x00 0x200>;
    interrupts = <0x00 0x02 0xf01>;
    interrupt-parent = <0xfde8>;
    dma-coherent;
    iommus = <0xfde9 0x01>;
};

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
---
!!! This patch is based on non upstreamed yet “Virtio support for toolstack
on Arm” V8 series which is on review now:
https://lore.kernel.org/xen-devel/1651598763-12162-1-git-send-email-olekstysh@xxxxxxxxx/

New device-tree binding (commit #5) is a part of solution to restrict memory
access under Xen using xen-grant DMA-mapping layer (which is also on review):
https://lore.kernel.org/xen-devel/1653944417-17168-1-git-send-email-olekstysh@xxxxxxxxx/

Changes RFC -> V1:
   - update commit description
   - rebase according to the recent changes to
     "libxl: Introduce basic virtio-mmio support on Arm"

Changes V1 -> V2:
   - Henry already gave his Reviewed-by, I dropped it due to the changes
   - use generic IOMMU device tree bindings instead of custom property
     "xen,dev-domid"
   - change commit subject and description, was
     "libxl/arm: Insert "xen,dev-domid" property to virtio-mmio device node"
---
 tools/libs/light/libxl_arm.c          | 49 ++++++++++++++++++++++++++++++++---
 xen/include/public/device_tree_defs.h |  1 +
 2 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
index 9be9b2a..72da3b1 100644
--- a/tools/libs/light/libxl_arm.c
+++ b/tools/libs/light/libxl_arm.c
@@ -865,9 +865,32 @@ static int make_vpci_node(libxl__gc *gc, void *fdt,
     return 0;
 }
 
+static int make_xen_iommu_node(libxl__gc *gc, void *fdt)
+{
+    int res;
+
+    /* See Linux Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml */
+    res = fdt_begin_node(fdt, "xen_iommu");
+    if (res) return res;
+
+    res = fdt_property_compat(gc, fdt, 1, "xen,grant-dma");
+    if (res) return res;
+
+    res = fdt_property_cell(fdt, "#iommu-cells", 1);
+    if (res) return res;
+
+    res = fdt_property_cell(fdt, "phandle", GUEST_PHANDLE_IOMMU);
+    if (res) return res;
+
+    res = fdt_end_node(fdt);
+    if (res) return res;
+
+    return 0;
+}
 
 static int make_virtio_mmio_node(libxl__gc *gc, void *fdt,
-                                 uint64_t base, uint32_t irq)
+                                 uint64_t base, uint32_t irq,
+                                 uint32_t backend_domid)
 {
     int res;
     gic_interrupt intr;
@@ -890,6 +913,16 @@ static int make_virtio_mmio_node(libxl__gc *gc, void *fdt,
     res = fdt_property(fdt, "dma-coherent", NULL, 0);
     if (res) return res;
 
+    if (backend_domid != LIBXL_TOOLSTACK_DOMID) {
+        uint32_t iommus_prop[2];
+
+        iommus_prop[0] = cpu_to_fdt32(GUEST_PHANDLE_IOMMU);
+        iommus_prop[1] = cpu_to_fdt32(backend_domid);
+
+        res = fdt_property(fdt, "iommus", iommus_prop, sizeof(iommus_prop));
+        if (res) return res;
+    }
+
     res = fdt_end_node(fdt);
     if (res) return res;
 
@@ -1097,6 +1130,7 @@ static int libxl__prepare_dtb(libxl__gc *gc, 
libxl_domain_config *d_config,
     size_t fdt_size = 0;
     int pfdt_size = 0;
     libxl_domain_build_info *const info = &d_config->b_info;
+    bool iommu_created;
     unsigned int i;
 
     const libxl_version_info *vers;
@@ -1204,11 +1238,20 @@ next_resize:
         if (d_config->num_pcidevs)
             FDT( make_vpci_node(gc, fdt, ainfo, dom) );
 
+        iommu_created = false;
         for (i = 0; i < d_config->num_disks; i++) {
             libxl_device_disk *disk = &d_config->disks[i];
 
-            if (disk->specification == LIBXL_DISK_SPECIFICATION_VIRTIO)
-                FDT( make_virtio_mmio_node(gc, fdt, disk->base, disk->irq) );
+            if (disk->specification == LIBXL_DISK_SPECIFICATION_VIRTIO) {
+                if (disk->backend_domid != LIBXL_TOOLSTACK_DOMID &&
+                    !iommu_created) {
+                    FDT( make_xen_iommu_node(gc, fdt) );
+                    iommu_created = true;
+                }
+
+                FDT( make_virtio_mmio_node(gc, fdt, disk->base, disk->irq,
+                                           disk->backend_domid) );
+            }
         }
 
         if (pfdt)
diff --git a/xen/include/public/device_tree_defs.h 
b/xen/include/public/device_tree_defs.h
index 209d43d..df58944 100644
--- a/xen/include/public/device_tree_defs.h
+++ b/xen/include/public/device_tree_defs.h
@@ -7,6 +7,7 @@
  * onwards. Reserve a high value for the GIC phandle.
  */
 #define GUEST_PHANDLE_GIC (65000)
+#define GUEST_PHANDLE_IOMMU (GUEST_PHANDLE_GIC + 1)
 
 #define GUEST_ROOT_ADDRESS_CELLS 2
 #define GUEST_ROOT_SIZE_CELLS 2
-- 
2.7.4