[xen staging] xen/dom0less: arm: fix hwdom 1:1 low memory allocation

[patchbot@xxxxxxx]

commit 2f6f9c7ae9de563764b0aaffa1abefc65c560a7a
Author:     Grygorii Strashko <grygorii_strashko@xxxxxxxx>
AuthorDate: Thu Aug 7 10:03:25 2025 +0000
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Tue Aug 12 12:04:41 2025 +0100

    xen/dom0less: arm: fix hwdom 1:1 low memory allocation
    
    Call stack for dom0less hwdom case (1:1) memory:
    create_domUs
    |-construct_domU
      |-construct_hwdom()
        |-allocate_memory_11()
    
    And allocate_memory_11() uses "dom0_mem" as:
    min_low_order =
      get_order_from_bytes(min_t(paddr_t, dom0_mem, MB(128)));
    
    In case of dom0less boot the "dom0_mem" is not used and defaulted to 0,
    which causes min_low_order to get high value > order and so no allocations
    happens from low memory.
    
    Fix it, by using kinfo->unassigned_mem instead of "dom0_mem" which has
    correct memory size in both cases: regular dom0 boot and dom0less boot.
    
    Fixes: 52cb53f1816a ("xen/arm: dom0less hwdom construction")
    Signed-off-by: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
    Reviewed-by: Denis Mukhin <dmukhin@xxxxxxxx>
    Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
    Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
---
 docs/misc/xen-command-line.pandoc | 3 ++-
 xen/arch/arm/domain_build.c       | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index a28a1b172b..a75b6c9301 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1035,7 +1035,8 @@ For example, with `dom0_max_vcpus=4-8`:
 > `= <size>`
 
 Set the amount of memory for the initial domain (dom0). It must be
-greater than zero. This parameter is required.
+greater than zero. This parameter is required (and only used) when the initial
+domain is not described in the Device-Tree.
 
 ### dom0_mem (x86)
 > `= List of ( min:<sz> | max:<sz> | <sz> )`
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 463ae4474d..a9e4153e3c 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -249,7 +249,7 @@ fail:
  *
  * We first allocate the largest allocation we can as low as we
  * can. This then becomes the first bank. This bank must be at least
- * 128MB (or dom0_mem if that is smaller).
+ * 128MB (or memory size requested for domain if that is smaller).
  *
  * Then we start allocating more memory, trying to allocate the
  * largest possible size and trying smaller sizes until we
@@ -278,7 +278,7 @@ static void __init allocate_memory_11(struct domain *d,
                                       struct kernel_info *kinfo)
 {
     const unsigned int min_low_order =
-        get_order_from_bytes(min_t(paddr_t, dom0_mem, MB(128)));
+        get_order_from_bytes(min_t(paddr_t, kinfo->unassigned_mem, MB(128)));
     const unsigned int min_order = get_order_from_bytes(MB(4));
     struct membanks *mem = kernel_info_get_mem(kinfo);
     struct page_info *pg;
--
generated by git-patchbot for /home/xen/git/xen.git#staging