a new field xloadflags was added to recent x86 linux, and BIT 1:
XLF_CAN_BE_LOADED_ABOVE_4G is used to tell bootload that where initrd can be
loaded safely.

Current QEMU/BIOS always loads initrd below below_4g_mem_size which is always
less than 4G, so here limiting initrd_max to 4G - 1 simply is enough if
this bit is set.

CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Richard Henderson <rth@twiddle.net>
CC: Eduardo Habkost <ehabkost@redhat.com>
CC: "Michael S. Tsirkin" <mst@redhat.com>
CC: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>

---
V3: correct grammar and check XLF_CAN_BE_LOADED_ABOVE_4G first (Michael S. Tsirkin)

Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
---
 hw/i386/pc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 8db7417..ebaa65f 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -897,7 +897,15 @@ static void load_linux(PCMachineState *pcms,
 #endif
 
     /* highest address for loading the initrd */
-    if (protocol >= 0x203) {
+    if (protocol >= 0x20c &&
+        lduw_p(header+0x236) & XLF_CAN_BE_LOADED_ABOVE_4G) {
+        /*
+         * Although kernel allows initrd loading to above 4G,
+         * it just makes it as large as possible while still staying below 4G
+         * since current BIOS always loads initrd below pcms->below_4g_mem_size
+         */
+        initrd_max = UINT32_MAX;
+    } else if (protocol >= 0x203) {
         initrd_max = ldl_p(header+0x22c);
     } else {
         initrd_max = 0x37ffffff;
-- 
2.7.4