2 files changed, 53 insertions, 1 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 65d8d79b46a8..399bed2de881 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -731,7 +731,6 @@ static void set_xen_basic_apic_ops(void)
 
 #endif
 
-
 static void xen_clts(void)
 {
         struct multicall_space mcs;
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index ad0047f47cd4..e0942630d47a 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -20,6 +20,7 @@
 #include <xen/page.h>
 #include <xen/interface/callback.h>
 #include <xen/interface/physdev.h>
+#include <xen/interface/memory.h>
 #include <xen/features.h>
 
 #include "xen-ops.h"
@@ -32,6 +33,56 @@ extern void xen_sysenter_target(void);
 extern void xen_syscall_target(void);
 extern void xen_syscall32_target(void);
 
+static unsigned long __init xen_release_chunk(phys_addr_t start_addr, phys_addr_t end_addr)
+{
+        struct xen_memory_reservation reservation = {
+                .address_bits = 0,
+                .extent_order = 0,
+                .domid        = DOMID_SELF
+        };
+        unsigned long *mfn_list = (unsigned long *)xen_start_info->mfn_list;
+        unsigned long start, end;
+        unsigned long len;
+        unsigned long pfn;
+        int ret;
+
+        start = PFN_UP(start_addr);
+        end = PFN_UP(end_addr);
+
+        if (end <= start)
+                return 0;
+
+        len = end - start;
+
+        set_xen_guest_handle(reservation.extent_start, &mfn_list[start]);
+        reservation.nr_extents = len;
+
+        ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
+        WARN(ret != (end - start), "Failed to release memory %lx-%lx err=%d\n",
+             start, end, ret);
+
+        for(pfn = start; pfn < end; pfn++)
+                set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
+
+        return len;
+}
+
+static unsigned long __init xen_return_unused_memory(const struct e820map *e820)
+{
+        unsigned long last_end = 0;
+        unsigned long released = 0;
+        int i;
+
+        for (i = 0; i < e820->nr_map; i++) {
+                released += xen_release_chunk(last_end, e820->map[i].addr);
+                last_end = e820->map[i].addr + e820->map[i].size;
+        }
+
+        released += xen_release_chunk(last_end, PFN_PHYS(xen_start_info->nr_pages));
+
+        printk(KERN_INFO "released %ld pages of unused memory\n", released);
+        return released;
+}
 
 /**
  * machine_specific_memory_setup - Hook for machine specific memory setup.
@@ -67,6 +118,8 @@ char * __init xen_memory_setup(void)
 
         sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
+        xen_return_unused_memory(&e820);
+
         return "Xen";
 }