xen: ask the hypervisor how much space it needs reserved

Ask the hypervisor how much space it needs reserved, since 32-on-64
doesn't need any space, and it may change in future.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 4186cb6a7f5a..bc7bf5f8d077 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1112,6 +1112,17 @@ static const struct machine_ops __initdata xen_machine_ops = {
 };
 
 
+static void __init xen_reserve_top(void)
+{
+        unsigned long top = HYPERVISOR_VIRT_START;
+        struct xen_platform_parameters pp;
+
+        if (HYPERVISOR_xen_version(XENVER_platform_parameters, &pp) == 0)
+                top = pp.virt_start;
+
+        reserve_top_address(-top + 2 * PAGE_SIZE);
+}
+
 /* First C function to be called on Xen boot */
 asmlinkage void __init xen_start_kernel(void)
 {
@@ -1169,7 +1180,7 @@ asmlinkage void __init xen_start_kernel(void)
                 pv_info.kernel_rpl = 0;
 
         /* set the limit of our address space */
-        reserve_top_address(-HYPERVISOR_VIRT_START + 2 * PAGE_SIZE);
+        xen_reserve_top();
 
         /* set up basic CPUID stuff */
         cpu_detect(&new_cpu_data);