Subject: fix balloon driver accounting for HVM-with-PoD case

With PoD, ballooning down a guest to the target set through xenstore
based on its totalram_pages value isn't sufficient, since that value
doesn't include all the pages assigned to the guest. Since the delta
is static, determine it once at load time.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- sle11-2010-01-12.orig/drivers/xen/balloon/balloon.c	2009-08-31 11:48:33.000000000 +0200
+++ sle11-2010-01-12/drivers/xen/balloon/balloon.c	2010-02-01 13:35:47.000000000 +0100
@@ -90,6 +90,18 @@ static unsigned long frame_list[PAGE_SIZ
 #define dec_totalhigh_pages() ((void)0)
 #endif
 
+#ifndef CONFIG_XEN
+/*
+ * In HVM guests accounting here uses the Xen visible values, but the kernel
+ * determined totalram_pages value shouldn't get altered. Since totalram_pages
+ * includes neither the kernel static image nor any memory allocated prior to
+ * or from the bootmem allocator, we have to synchronize the two values.
+ */
+static unsigned long __read_mostly totalram_bias;
+#else
+#define totalram_bias 0
+#endif
+
 /* List of ballooned pages, threaded through the mem_map array. */
 static LIST_HEAD(ballooned_pages);
 
@@ -305,7 +317,7 @@ static int increase_reservation(unsigned
 	}
 
 	bs.current_pages += rc;
-	totalram_pages = bs.current_pages;
+	totalram_pages = bs.current_pages - totalram_bias;
 
  out:
 	balloon_unlock(flags);
@@ -385,7 +397,7 @@ static int decrease_reservation(unsigned
 	BUG_ON(ret != nr_pages);
 
 	bs.current_pages -= nr_pages;
-	totalram_pages = bs.current_pages;
+	totalram_pages = bs.current_pages - totalram_bias;
 
 	balloon_unlock(flags);
 
@@ -524,7 +536,19 @@ static struct notifier_block xenstore_no
 
 static int __init balloon_init(void)
 {
-#if defined(CONFIG_X86) && defined(CONFIG_XEN) 
+#if !defined(CONFIG_XEN)
+# ifndef XENMEM_get_pod_target
+#  define XENMEM_get_pod_target 17
+	typedef struct xen_pod_target {
+		uint64_t target_pages;
+		uint64_t tot_pages;
+		uint64_t pod_cache_pages;
+		uint64_t pod_entries;
+		domid_t domid;
+	} xen_pod_target_t;
+# endif
+	xen_pod_target_t pod_target = { .domid = DOMID_SELF };
+#elif defined(CONFIG_X86)
 	unsigned long pfn;
 	struct page *page;
 #endif
@@ -538,7 +562,20 @@ static int __init balloon_init(void)
 	bs.current_pages = min(xen_start_info->nr_pages, max_pfn);
 	totalram_pages   = bs.current_pages;
 #else 
-	bs.current_pages = totalram_pages; 
+	totalram_bias = HYPERVISOR_memory_op(
+		HYPERVISOR_memory_op(XENMEM_get_pod_target,
+			&pod_target) != -ENOSYS
+		? XENMEM_maximum_reservation
+		: XENMEM_current_reservation,
+		&pod_target.domid);
+	if ((long)totalram_bias != -ENOSYS) {
+		BUG_ON(totalram_bias < totalram_pages);
+		bs.current_pages = totalram_bias;
+		totalram_bias -= totalram_pages;
+	} else {
+		totalram_bias = 0;
+		bs.current_pages = totalram_pages;
+	}
 #endif
 	bs.target_pages  = bs.current_pages;
 	bs.balloon_low   = 0;
@@ -671,7 +708,7 @@ struct page **alloc_empty_pages_and_page
 			goto err;
 		}
 
-		totalram_pages = --bs.current_pages;
+		totalram_pages = --bs.current_pages - totalram_bias;
 
 		balloon_unlock(flags);
 	}