[xen staging] xen/arm: Prevent Dom0 to be loaded when using dom0less

[patchbot@xxxxxxx]

commit fcb97d1f19ab294df091249399e515117350c228
Author:     Luca Fancellu <luca.fancellu@xxxxxxx>
AuthorDate: Wed Apr 14 10:14:04 2021 +0100
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Thu Apr 15 18:08:57 2021 +0100

    xen/arm: Prevent Dom0 to be loaded when using dom0less
    
    This patch prevents the dom0 to be loaded skipping its
    building and going forward to build domUs when the dom0
    kernel is not found and at least one domU is present.
    
    Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
---
 docs/features/dom0less.pandoc |  7 ++++---
 xen/arch/arm/setup.c          | 42 +++++++++++++++++++++++++++++++++++++++---
 2 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/docs/features/dom0less.pandoc b/docs/features/dom0less.pandoc
index d798596cdf..c9edb529e1 100644
--- a/docs/features/dom0less.pandoc
+++ b/docs/features/dom0less.pandoc
@@ -16,9 +16,10 @@ Multiboot specification has been extended to allow for 
multiple domains
 to be passed to Xen. See docs/misc/arm/device-tree/booting.txt for more
 information about the Multiboot specification and how to use it.
 
-Currently, a control domain ("dom0") is still required, but in the
-future it will become unnecessary when all domains are created
-directly from Xen. Instead of waiting for the control domain to be fully
+Currently, a control domain ("dom0") is still required to manage the DomU
+domains, but the system can start also without dom0 if the Device Tree
+doesn't specify the dom0 kernel and it declares one or more domUs.
+Instead of waiting for the control domain (when declared) to be fully
 booted and the Xen tools to become available, domains created by Xen
 this way are started right away in parallel. Hence, their boot time is
 typically much shorter.
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 70a719cbaf..00aad1c194 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -794,6 +794,38 @@ static void __init setup_mm(void)
 }
 #endif
 
+static bool __init is_dom0less_mode(void)
+{
+    struct bootmodules *mods = &bootinfo.modules;
+    struct bootmodule *mod;
+    unsigned int i;
+    bool dom0found = false;
+    bool domUfound = false;
+
+    /* Look into the bootmodules */
+    for ( i = 0 ; i < mods->nr_mods ; i++ )
+    {
+        mod = &mods->module[i];
+        /* Find if dom0 and domU kernels are present */
+        if ( mod->kind == BOOTMOD_KERNEL )
+        {
+            if ( mod->domU == false )
+            {
+                dom0found = true;
+                break;
+            }
+            else
+                domUfound = true;
+        }
+    }
+
+    /*
+     * If there is no dom0 kernel but at least one domU, then we are in
+     * dom0less mode
+     */
+    return ( !dom0found && domUfound );
+}
+
 size_t __read_mostly dcache_line_bytes;
 
 /* C entry point for boot CPU */
@@ -804,7 +836,7 @@ void __init start_xen(unsigned long boot_phys_offset,
     int cpus, i;
     const char *cmdline;
     struct bootmodule *xen_bootmodule;
-    struct domain *dom0;
+    struct domain *dom0 = NULL;
     int rc;
 
     dcache_line_bytes = read_dcache_line_bytes();
@@ -959,7 +991,10 @@ void __init start_xen(unsigned long boot_phys_offset,
     enable_errata_workarounds();
 
     /* Create initial domain 0. */
-    dom0 = create_dom0();
+    if ( !is_dom0less_mode() )
+        dom0 = create_dom0();
+    else
+        printk(XENLOG_INFO "Xen dom0less mode detected\n");
 
     heap_init_late();
 
@@ -977,7 +1012,8 @@ void __init start_xen(unsigned long boot_phys_offset,
     if ( acpi_disabled )
         create_domUs();
 
-    domain_unpause_by_systemcontroller(dom0);
+    if ( dom0 )
+        domain_unpause_by_systemcontroller(dom0);
 
     /* Switch on to the dynamically allocated stack for the idle vcpu
      * since the static one we're running on is about to be freed. */
--
generated by git-patchbot for /home/xen/git/xen.git#staging