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 <pbonz...@redhat.com> CC: Richard Henderson <r...@twiddle.net> CC: Eduardo Habkost <ehabk...@redhat.com> CC: "Michael S. Tsirkin" <m...@redhat.com> CC: Marcel Apfelbaum <marcel.apfelb...@gmail.com> Signed-off-by: Li Zhijian <lizhij...@cn.fujitsu.com> --- V3: correct grammar and check XLF_CAN_BE_LOADED_ABOVE_4G first (Michael S. Tsirkin) Signed-off-by: Li Zhijian <lizhij...@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 3b10726..baa99c0 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -904,7 +904,15 @@ 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