xen: allow balloon driver to use more than one memory region

Allow the xen balloon driver to populate its list of extra pages from
more than one region of memory.  This will allow platforms to provide
(for example) a region of low memory and a region of high memory.

The maximum possible number of extra regions is 128 (== E820MAX) which
is quite large so xen_extra_mem is placed in __initdata.  This is safe
as both xen_memory_setup() and balloon_init() are in __init.

The balloon regions themselves are not altered (i.e., there is still
only the one region).

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 27 insertions, 17 deletions

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 9efb993090aa..fc43b53651d7 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -555,11 +555,32 @@ void free_xenballooned_pages(int nr_pages, struct page** pages)
 }
 EXPORT_SYMBOL(free_xenballooned_pages);
 
-static int __init balloon_init(void)
+static void __init balloon_add_region(unsigned long start_pfn,
+				      unsigned long pages)
 {
 	unsigned long pfn, extra_pfn_end;
 	struct page *page;
 
+	/*
+	 * If the amount of usable memory has been limited (e.g., with
+	 * the 'mem' command line parameter), don't add pages beyond
+	 * this limit.
+	 */
+	extra_pfn_end = min(max_pfn, start_pfn + pages);
+
+	for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
+		page = pfn_to_page(pfn);
+		/* totalram_pages and totalhigh_pages do not
+		   include the boot-time balloon extension, so
+		   don't subtract from it. */
+		__balloon_append(page);
+	}
+}
+
+static int __init balloon_init(void)
+{
+	int i;
+
 	if (!xen_domain())
 		return -ENODEV;
 
@@ -587,23 +608,12 @@ static int __init balloon_init(void)
 
 	/*
 	 * Initialize the balloon with pages from the extra memory
-	 * region (see arch/x86/xen/setup.c).
-	 *
-	 * If the amount of usable memory has been limited (e.g., with
-	 * the 'mem' command line parameter), don't add pages beyond
-	 * this limit.
+	 * regions (see arch/x86/xen/setup.c).
 	 */
-	extra_pfn_end = min(max_pfn,
-			    (unsigned long)PFN_DOWN(xen_extra_mem_start
-						    + xen_extra_mem_size));
-	for (pfn = PFN_UP(xen_extra_mem_start);
-	     pfn < extra_pfn_end;
-	     pfn++) {
-		page = pfn_to_page(pfn);
-		/* totalram_pages and totalhigh_pages do not include the boot-time
-		   balloon extension, so don't subtract from it. */
-		__balloon_append(page);
-	}
+	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
+		if (xen_extra_mem[i].size)
+			balloon_add_region(PFN_UP(xen_extra_mem[i].start),
+					   PFN_DOWN(xen_extra_mem[i].size));
 
 	return 0;
 }