xen: add CONFIG item for default dom0 memory size

With being able to specify a dom0_mem value depending on host memory
size on x86 make it easy for distros to specify a default dom0 size by
adding a CONFIG_DOM0_MEM item which presets the dom0_mem boot parameter
value.

It will be used only if no dom0_mem parameter was specified in the
boot parameters.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <julien.grall@arm.com>

xen/arch/arm/domain_build.c

@@ -32,9 +32,12 @@ static unsigned int __initdata opt_dom0_max_vcpus;
 integer_param("dom0_max_vcpus", opt_dom0_max_vcpus);
 
 static u64 __initdata dom0_mem;
+static bool __initdata dom0_mem_set;
 
 static int __init parse_dom0_mem(const char *s)
 {
+    dom0_mem_set = true;
+
     dom0_mem = parse_size_and_unit(s, &s);
 
     return *s ? -EINVAL : 0;
@@ -2114,6 +2117,10 @@ int __init construct_dom0(struct domain *d)
     BUG_ON(d->domain_id != 0);
 
     printk("*** LOADING DOMAIN 0 ***\n");
+
+    if ( !dom0_mem_set && CONFIG_DOM0_MEM[0] )
+        parse_dom0_mem(CONFIG_DOM0_MEM);
+
     if ( dom0_mem <= 0 )
     {
         warning_add("PLEASE SPECIFY dom0_mem PARAMETER - USING 512M FOR NOW\n");

xen/arch/x86/dom0_build.c

@@ -29,6 +29,7 @@ struct memsize {
 static struct memsize __initdata dom0_size;
 static struct memsize __initdata dom0_min_size;
 static struct memsize __initdata dom0_max_size = { .nr_pages = LONG_MAX };
+static bool __initdata dom0_mem_set;
 
 static bool __init memsize_gt_zero(const struct memsize *sz)
 {
@@ -117,6 +118,8 @@ static int __init parse_dom0_mem(const char *s)
 {
     int ret;
 
+    dom0_mem_set = true;
+
     /* xen-shim uses shim_mem parameter instead of dom0_mem */
     if ( pv_shim )
     {
@@ -339,6 +342,9 @@ unsigned long __init dom0_compute_nr_pages(
     unsigned long avail = 0, nr_pages, min_pages, max_pages;
     bool need_paging;
 
+    if ( !dom0_mem_set && CONFIG_DOM0_MEM[0] )
+        parse_dom0_mem(CONFIG_DOM0_MEM);
+
     for_each_node_mask ( node, dom0_nodes )
         avail += avail_domheap_pages_region(node, 0, 0) +
                  initial_images_nrpages(node);

xen/common/Kconfig

@@ -323,4 +323,17 @@ config CMDLINE_OVERRIDE
 
 	  This is used to work around broken bootloaders. This should
 	  be set to 'N' under normal conditions.
+
+config DOM0_MEM
+	string "Default value for dom0_mem boot parameter"
+	default ""
+	---help---
+	  Sets a default value for dom0_mem, e.g. "512M".
+	  The specified string will be used for the dom0_mem parameter in
+	  case it was not specified on the command line.
+
+	  See docs/misc/xen-command-line.markdown for the supported syntax.
+
+	  Leave empty if you are not sure what to specify.
+
 endmenu