From aab50e53440b2fe432a5a59cbd0e7ec241a1169b Mon Sep 17 00:00:00 2001 From: Li Zhijian Date: Thu, 17 Jan 2019 20:49:04 +0800 Subject: [PATCH] i386: allow to load initrd below 4 GB for recent linux Since linux commit: cf8fa920cb42 ("i386: handle an initrd in highmem (version 2)") linux has supported initrd up to 4 GB, but the header field ramdisk_max is still set to 2 GB to avoid "possible bootloader bugs". When use '-kernel vmlinux -initrd initrd.cgz' to launch a VM, the firmware(it could be linuxboot_dma.bin) helps to read initrd contents into guest memory(below ramdisk_max) and jump to kernel. that's similar with what bootloader does, like grub. In addition, initrd_max is uint32_t simply because QEMU doesn't support the 64-bit boot protocol (specifically the ext_ramdisk_image field). Therefore here just limit initrd_max to UINT32_MAX simply as well to allow initrd to be loaded below 4 GB. NOTE: it's possible that linux protocol within [0x208, 0x20c] supports up to 4 GB initrd as well. CC: Paolo Bonzini CC: Richard Henderson CC: Eduardo Habkost CC: "Michael S. Tsirkin" CC: Marcel Apfelbaum Signed-off-by: Li Zhijian Reviewed-by: Eduardo Habkost Reviewed-by: Stefano Garzarella Signed-off-by: Paolo Bonzini --- hw/i386/pc.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 9664822fc8..7d8f351b1d 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -1299,7 +1299,26 @@ 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) { + /* + * Linux has supported initrd up to 4 GB for a very long time (2007, + * long before XLF_CAN_BE_LOADED_ABOVE_4G which was added in 2013), + * though it only sets initrd_max to 2 GB to "work around bootloader + * bugs". Luckily, QEMU firmware(which does something like bootloader) + * has supported this. + * + * It's believed that if XLF_CAN_BE_LOADED_ABOVE_4G is set, initrd can + * be loaded into any address. + * + * In addition, initrd_max is uint32_t simply because QEMU doesn't + * support the 64-bit boot protocol (specifically the ext_ramdisk_image + * field). + * + * Therefore here just limit initrd_max to UINT32_MAX simply as well. + */ + initrd_max = UINT32_MAX; + } else if (protocol >= 0x203) { initrd_max = ldl_p(header+0x22c); } else { initrd_max = 0x37ffffff; -- 2.11.0