xen/pvh: do not mark the low 1MB as IO mem

On PVH there's nothing special on the low 1MB.

This is an optional patch that doesn't affect the functionality of the
shim.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index a21a668d735c8da3f5a2c604597386a9251332e0..1147a1afb1bc31ce544d0c76022b48461a8dadf6 100644 (file)
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -122,6 +122,7 @@
 #include <asm/fixmap.h>
 #include <asm/io_apic.h>
 #include <asm/pci.h>
+#include <asm/guest.h>
 
 #include <asm/hvm/grant_table.h>
 #include <asm/pv/grant_table.h>
@@ -288,8 +289,12 @@ void __init arch_init_memory(void)
     dom_cow = domain_create(DOMID_COW, DOMCRF_dummy, 0, NULL);
     BUG_ON(IS_ERR(dom_cow));
 
-    /* First 1MB of RAM is historically marked as I/O. */
-    for ( i = 0; i < 0x100; i++ )
+    /*
+     * First 1MB of RAM is historically marked as I/O.  If we booted PVH,
+     * reclaim the space.  Irrespective, leave MFN 0 as special for the sake
+     * of 0 being a very common default value.
+     */
+    for ( i = 0; i < (pvh_boot ? 1 : 0x100); i++ )
         share_xen_page_with_guest(mfn_to_page(_mfn(i)),
                                   dom_io, XENSHARE_writable);