[Qemu-devel] [PATCH 3/3] x86: allow load initrd below 4G for recent linux

[Li Zhijian]

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 saftly.

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

CC: Paolo Bonzini <address@hidden>
CC: Richard Henderson <address@hidden>
CC: Eduardo Habkost <address@hidden>
CC: "Michael S. Tsirkin" <address@hidden>
CC: Marcel Apfelbaum <address@hidden>
Signed-off-by: Li Zhijian <address@hidden>
---
 hw/i386/pc.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index f095725..5e2f83c 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -92,6 +92,7 @@
 #define FW_CFG_HPET (FW_CFG_ARCH_LOCAL + 4)
 
 #define E820_NR_ENTRIES                16
+#define XLF_CAN_BE_LOADED_ABOVE_4G_MASK (1 << 1)
 
 struct e820_entry {
     uint64_t address;
@@ -916,6 +917,17 @@ static void load_linux(PCMachineState *pcms,
     } else {
         initrd_max = 0x37ffffff;
     }
+    if (protocol >= 0x20c) {
+        unsigned int xloadflags = lduw_p(header+0x236);
+        if (xloadflags & XLF_CAN_BE_LOADED_ABOVE_4G_MASK) {
+                /*
+                 * Although kernel allow initrd loading to above 4G, here we
+                 * limit initrd_max to 4G -1 due to current QEMU always loads
+                 * initrd below pcms->below_4g_mem_size
+                 */
+                initrd_max = UINT32_MAX;
+        }
+    }
 
     if (initrd_max >= pcms->below_4g_mem_size - pcmc->acpi_data_size) {
         initrd_max = pcms->below_4g_mem_size - pcmc->acpi_data_size - 1;
-- 
2.7.4