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 <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> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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hw/i386/pc.c
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hw/i386/pc.c
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@ -1299,7 +1299,26 @@ static void load_linux(PCMachineState *pcms,
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#endif
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/* highest address for loading the initrd */
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if (protocol >= 0x203) {
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if (protocol >= 0x20c &&
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lduw_p(header+0x236) & XLF_CAN_BE_LOADED_ABOVE_4G) {
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/*
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* Linux has supported initrd up to 4 GB for a very long time (2007,
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* long before XLF_CAN_BE_LOADED_ABOVE_4G which was added in 2013),
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* though it only sets initrd_max to 2 GB to "work around bootloader
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* bugs". Luckily, QEMU firmware(which does something like bootloader)
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* has supported this.
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*
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* It's believed that if XLF_CAN_BE_LOADED_ABOVE_4G is set, initrd can
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* be loaded into any address.
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*
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* In addition, initrd_max is uint32_t simply because QEMU doesn't
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* support the 64-bit boot protocol (specifically the ext_ramdisk_image
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* field).
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*
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* Therefore here just limit initrd_max to UINT32_MAX simply as well.
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*/
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initrd_max = UINT32_MAX;
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} else if (protocol >= 0x203) {
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initrd_max = ldl_p(header+0x22c);
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} else {
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initrd_max = 0x37ffffff;
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