| Message ID | 1547729344-3895-5-git-send-email-lizhijian@cn.fujitsu.com |
|---|---|
| State | New |
| Headers | show |
| Series | allow to load initrd below 4G for recent kernel | expand |
On Thu, Jan 17, 2019 at 08:49:04PM +0800, Li Zhijian wrote: > 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> Michael, should this go through your tree?
On Thu, Jan 17, 2019 at 08:49:04PM +0800, Li Zhijian wrote: > 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> > > --- > V6: update comments > V5: udpate comments and changelog > 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 | 21 ++++++++++++++++++++- > 1 file changed, 20 insertions(+), 1 deletion(-) Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
diff --git a/hw/i386/pc.c b/hw/i386/pc.c index 64d23b2..10977a3 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -1130,7 +1130,26 @@ 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;
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> --- V6: update comments V5: udpate comments and changelog 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 | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-)