[PATCH v1 1/3] xen/dom0less: introduce free_phandle in struct kernel_info

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

There are cases where it is necessary to know the next available phandle
number in order to generate phandles for guest device nodes.

When a partial FDT (pfdt) is provided, special care is needed during
initialization of free_phandle, as the pfdt may already contain a dummy
interrupt controller node with a phandle assigned to it.  free_phandle
must therefore be initialized to one past the highest phandle already
present in the pfdt, to avoid collisions.

Since free_phandle may be needed for the very first guest node generated,
domain_handle_dtb_boot_module() is moved earlier in prepare_dtb_domU().
The new call site also aligns better with the existing comment stating
that domain_handle_dtb_boot_module() must be called before the rest of
the device tree is generated.

Introduce get_next_free_phandle() to ensure that phandles allocated for
guest nodes do not overlap the Xen-reserved phandle range.  This helper
will be used by subsequent patches (by RISC-V at the moment).

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/common/device-tree/dom0less-build.c | 44 ++++++++++++++++++-------
 xen/include/xen/fdt-domain-build.h      |  6 ++++
 xen/include/xen/fdt-kernel.h            |  3 ++
 3 files changed, 41 insertions(+), 12 deletions(-)

diff --git a/xen/common/device-tree/dom0less-build.c 
b/xen/common/device-tree/dom0less-build.c
index 840d14419da2..9205f01f0a49 100644
--- a/xen/common/device-tree/dom0less-build.c
+++ b/xen/common/device-tree/dom0less-build.c
@@ -389,6 +389,24 @@ static int __init domain_handle_dtb_boot_module(struct 
domain *d,
     if ( res < 0 )
         goto out;
 
+    /*
+     * Find the highest phandle in the partial FDT so free_phandle starts
+     * above it, avoiding collisions with pfdt's own phandle assignments.
+     */
+    res = fdt_generate_phandle(pfdt, &kinfo->free_phandle);
+    if ( res )
+    {
+        res = (res == -FDT_ERR_NOPHANDLES) ? -EOVERFLOW : -EINVAL;
+        goto out;
+    }
+
+    if ( kinfo->free_phandle >= GUEST_PHANDLE_GIC )
+    {
+        dprintk(XENLOG_ERR, "Phandle allocation overlaps Xen reserved 
range\n");
+        res = -EOVERFLOW;
+        goto out;
+    }
+
     for ( node_next = fdt_first_subnode(pfdt, 0);
           node_next > 0;
           node_next = fdt_next_subnode(pfdt, node_next) )
@@ -459,6 +477,8 @@ static int __init prepare_dtb_domU(struct domain *d, struct 
kernel_info *kinfo)
     BUILD_BUG_ON(DOMU_DTB_SIZE > SZ_2M);
 
     kinfo->phandle_intc = GUEST_PHANDLE_GIC;
+    kinfo->free_phandle = 1;
+    BUILD_BUG_ON(GUEST_PHANDLE_GIC == 1);
 
 #ifdef CONFIG_GRANT_TABLE
     kinfo->gnttab_start = GUEST_GNTTAB_BASE;
@@ -499,6 +519,18 @@ static int __init prepare_dtb_domU(struct domain *d, 
struct kernel_info *kinfo)
     if ( ret )
         goto err;
 
+    /*
+     * domain_handle_dtb_boot_module() must be called before the rest of the
+     * device tree is generated because it sets phandle_intc and free_phandle,
+     * which subsequent node generation depends on.
+     */
+    if ( kinfo->dtb )
+    {
+        ret = domain_handle_dtb_boot_module(d, kinfo);
+        if ( ret )
+            goto err;
+    }
+
     ret = make_chosen_node(kinfo);
     if ( ret )
         goto err;
@@ -516,18 +548,6 @@ static int __init prepare_dtb_domU(struct domain *d, 
struct kernel_info *kinfo)
     if ( ret )
         goto err;
 
-    /*
-     * domain_handle_dtb_boot_module has to be called before the rest of
-     * the device tree is generated because it depends on the value of
-     * the field phandle_intc.
-     */
-    if ( kinfo->dtb )
-    {
-        ret = domain_handle_dtb_boot_module(d, kinfo);
-        if ( ret )
-            goto err;
-    }
-
     ret = make_intc_domU_node(kinfo);
     if ( ret )
         goto err;
diff --git a/xen/include/xen/fdt-domain-build.h 
b/xen/include/xen/fdt-domain-build.h
index 1d9e77df0eb3..220ae46ddbe1 100644
--- a/xen/include/xen/fdt-domain-build.h
+++ b/xen/include/xen/fdt-domain-build.h
@@ -63,6 +63,12 @@ int find_unallocated_memory(const struct kernel_info *kinfo,
                                       unsigned long e_gfn,
                                       void *data));
 
+/* Return 0 (invalid phandle) if the Xen-reserved range has been reached */
+static inline uint32_t get_next_free_phandle(struct kernel_info *kinfo)
+{
+    return kinfo->free_phandle >= GUEST_PHANDLE_GIC ? 0 : 
kinfo->free_phandle++;
+}
+
 #endif /* __XEN_FDT_DOMAIN_BUILD_H__ */
 
 /*
diff --git a/xen/include/xen/fdt-kernel.h b/xen/include/xen/fdt-kernel.h
index aa977a50f4fc..3527934b2a00 100644
--- a/xen/include/xen/fdt-kernel.h
+++ b/xen/include/xen/fdt-kernel.h
@@ -44,6 +44,9 @@ struct kernel_info {
     /* Interrupt controller phandle */
     uint32_t phandle_intc;
 
+    /* Next free phandle available for assigning to guest device nodes */
+    uint32_t free_phandle;
+
     /* loader to use for this kernel */
     void (*load)(struct kernel_info *info);
 
-- 
2.53.0