[RFC PATCH] libxl/arm: Insert "xen,dev-domid" property to virtio-mmio device node

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

This is needed for grant table based DMA ops layer (CONFIG_XEN_VIRTIO)
at the guest side to retrieve the ID of Xen domain where the corresponding
backend resides (it is used as an argument to the grant table APIs).

This is a part of restricted memory access under Xen feature.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
---
!!! This patch is based on non upstreamed yet “Virtio support for toolstack
on Arm” series which is on review now:
https://lore.kernel.org/xen-devel/1649442065-8332-1-git-send-email-olekstysh@xxxxxxxxx/

All details are at:
https://lore.kernel.org/xen-devel/1649963973-22879-1-git-send-email-olekstysh@xxxxxxxxx/
---
 tools/libs/light/libxl_arm.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
index 8132a47..d9b26fc 100644
--- a/tools/libs/light/libxl_arm.c
+++ b/tools/libs/light/libxl_arm.c
@@ -875,7 +875,8 @@ static int make_vpci_node(libxl__gc *gc, void *fdt,
 
 
 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;
@@ -900,6 +901,14 @@ 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 domid[1];
+
+        domid[0] = cpu_to_fdt32(backend_domid);
+        res = fdt_property(fdt, "xen,dev-domid", domid, sizeof(domid));
+        if (res) return res;
+    }
+
     res = fdt_end_node(fdt);
     if (res) return res;
 
@@ -1218,7 +1227,8 @@ next_resize:
             libxl_device_disk *disk = &d_config->disks[i];
 
             if (disk->protocol == LIBXL_DISK_PROTOCOL_VIRTIO_MMIO)
-                FDT( make_virtio_mmio_node(gc, fdt, disk->base, disk->irq) );
+                FDT( make_virtio_mmio_node(gc, fdt, disk->base, disk->irq,
+                                           disk->backend_domid) );
         }
 
         if (pfdt)
-- 
2.7.4