[RFCv2 26/38] x86/hyperlaunch: introduce domain builder general dom creation

["Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>]

Introduce the builder_create_domains() function that provides the general
domain construction abstraction that selects between classic dom0 construction
and the hyperlaunch domain builder.

Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
---
 xen/arch/x86/domain-builder/Makefile |  1 +
 xen/arch/x86/domain-builder/core.c   | 36 ++++++++++++++++++++++++++++
 xen/arch/x86/include/asm/bootinfo.h  | 26 ++++++++++++++++++++
 xen/arch/x86/setup.c                 | 23 +++++++++++++++---
 xen/include/xen/domain-builder.h     |  2 ++
 5 files changed, 85 insertions(+), 3 deletions(-)
 create mode 100644 xen/arch/x86/domain-builder/core.c

diff --git a/xen/arch/x86/domain-builder/Makefile 
b/xen/arch/x86/domain-builder/Makefile
index 69a7c574a8d8..96040bf66a04 100644
--- a/xen/arch/x86/domain-builder/Makefile
+++ b/xen/arch/x86/domain-builder/Makefile
@@ -1 +1,2 @@
+obj-y += core.o
 obj-y += domain.o
diff --git a/xen/arch/x86/domain-builder/core.c 
b/xen/arch/x86/domain-builder/core.c
new file mode 100644
index 000000000000..3b315e59b188
--- /dev/null
+++ b/xen/arch/x86/domain-builder/core.c
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2025, Apertus Solutions, LLC
+ */
+
+#include <xen/domain-builder.h>
+#include <xen/init.h>
+#include <xen/lib.h>
+
+#include <asm/bootinfo.h>
+
+unsigned int __init builder_create_domains(struct boot_info *bi)
+{
+    unsigned int build_count = 0;
+    struct boot_domain *bd = &bi->domains[0];
+
+    if ( bd->capabilities & DOMAIN_CAPS_HARDWARE && bd->kernel == NULL )
+        panic("%s: hardware domain missing kernel\n", __func__);
+
+
+    arch_create_dom(bi, bd);
+    if ( bd->d )
+        build_count++;
+
+    return build_count;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/arch/x86/include/asm/bootinfo.h 
b/xen/arch/x86/include/asm/bootinfo.h
index 5b2c93b1ef9e..430ae08cf5ef 100644
--- a/xen/arch/x86/include/asm/bootinfo.h
+++ b/xen/arch/x86/include/asm/bootinfo.h
@@ -132,6 +132,32 @@ static inline unsigned int __init next_boot_module_index(
           (i) <= (b)->nr_modules;                       \
           (i) = next_boot_module_index(b, t, i + 1) )
 
+/*
+ * next_boot_domain_index:
+ *     Finds the next boot domain with capability cap, starting at array index
+ *     start.
+ *
+ * Returns:
+ *      Success - index in boot_domains array
+ *      Failure - a value greater than MAX_NR_BOOTDOMS
+ */
+static inline unsigned int __init next_boot_domain_index(
+    const struct boot_info *bi, uint32_t cap, unsigned int start)
+{
+    int i;
+
+    for ( i = start; i < bi->nr_domains; i++ )
+    {
+        if ( bi->domains[i].capabilities & cap )
+            return i;
+    }
+
+    return MAX_NR_BOOTDOMS + 1;
+}
+
+#define first_boot_domain_index(bi, cap)              \
+    next_boot_domain_index(bi, cap, 0)
+
 #endif /* X86_BOOTINFO_H */
 
 /*
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 2458a43902e6..b2c7846be18f 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -2026,9 +2026,26 @@ void asmlinkage __init noreturn __start_xen(void)
      * We're going to setup domain0 using the module(s) that we stashed safely
      * above our heap. The second module, if present, is an initrd ramdisk.
      */
-    dom0 = arch_create_dom(bi, &bi->domains[0]);
-    if ( !dom0 )
-        panic("Could not set up DOM0 guest OS\n");
+    ret = builder_create_domains(bi);
+    if ( ret <= 0 )
+        panic("Could not set up boot-time domains\n");
+    else
+        printk(XENLOG_INFO "Constructed %d boot-time domains\n", ret);
+
+    /* Selection order: hardware domain, control domain, first domain */
+    i = first_boot_domain_index(bi, DOMAIN_CAPS_HARDWARE);
+    if ( i >= MAX_NR_BOOTDOMS )
+    {
+        i = first_boot_domain_index(bi, DOMAIN_CAPS_CONTROL);
+        if ( i >= MAX_NR_BOOTDOMS )
+        {
+            printk(XENLOG_WARNING
+                   "A hwdom/ctrldom not detected, using 0th domain\n");
+            i = 0;
+        }
+    }
+
+    dom0 = bi->domains[i].d;
 
     heap_init_late();
 
diff --git a/xen/include/xen/domain-builder.h b/xen/include/xen/domain-builder.h
index a9df326682ac..c26f670d4f66 100644
--- a/xen/include/xen/domain-builder.h
+++ b/xen/include/xen/domain-builder.h
@@ -43,4 +43,6 @@ void domain_vcpus_create(struct domain *d);
 struct domain *arch_create_dom(
     struct boot_info *bi, struct boot_domain *bd);
 
+unsigned int builder_create_domains(struct boot_info *bi);
+
 #endif /* __XEN_DOMAIN_BUILDER_H__ */
-- 
2.30.2