[PATCH for-4.19(?)] xen/arm: bootfdt: Fix device tree memory node probing

[Michal Orzel <michal.orzel@xxxxxxx>]

Memory node probing is done as part of early_scan_node() that is called
for each node with depth >= 1 (root node is at depth 0). According to
Devicetree Specification v0.4, chapter 3.4, /memory node can only exists
as a top level node. However, Xen incorrectly considers all the nodes with
unit node name "memory" as RAM. This buggy behavior can result in a
failure if there are other nodes in the device tree (at depth >= 2) with
"memory" as unit node name. An example can be a "memory@xxx" node under
/reserved-memory. Fix it by introducing device_tree_is_memory_node() to
perform all the required checks to assess if a node is a proper /memory
node.

Fixes: 3e99c95ba1c8 ("arm, device tree: parse the DTB for RAM location and 
size")
Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
---
4.19: This patch is fixing a possible early boot Xen failure (before main
console is initialized). In my case it results in a warning "Shattering
superpage is not supported" and panic "Unable to setup the directmap mappings".

If this is too late for this patch to go in, we can backport it after the tree
re-opens.
---
 xen/arch/arm/bootfdt.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c
index 6e060111d95b..23c968e6955d 100644
--- a/xen/arch/arm/bootfdt.c
+++ b/xen/arch/arm/bootfdt.c
@@ -83,6 +83,32 @@ static bool __init device_tree_node_compatible(const void 
*fdt, int node,
     return false;
 }
 
+/*
+ * Check if a node is a proper /memory node according to Devicetree
+ * Specification v0.4, chapter 3.4.
+ */
+static bool __init device_tree_is_memory_node(const void *fdt, int node,
+                                              int depth)
+{
+    const char *type;
+    int len;
+
+    if ( depth != 1 )
+        return false;
+
+    if ( !device_tree_node_matches(fdt, node, "memory") )
+        return false;
+
+    type = fdt_getprop(fdt, node, "device_type", &len);
+    if ( !type )
+        return false;
+
+    if ( (len <= 0) || strcmp(type, "memory") )
+        return false;
+
+    return true;
+}
+
 void __init device_tree_get_reg(const __be32 **cell, uint32_t address_cells,
                                 uint32_t size_cells, paddr_t *start,
                                 paddr_t *size)
@@ -448,7 +474,7 @@ static int __init early_scan_node(const void *fdt,
      * populated. So we should skip the parsing.
      */
     if ( !efi_enabled(EFI_BOOT) &&
-         device_tree_node_matches(fdt, node, "memory") )
+         device_tree_is_memory_node(fdt, node, depth) )
         rc = process_memory_node(fdt, node, name, depth,
                                  address_cells, size_cells, 
bootinfo_get_mem());
     else if ( depth == 1 && !dt_node_cmp(name, "reserved-memory") )
-- 
2.25.1