On 09/11/2018 10:57, Li Zhijian wrote: > On 11/9/2018 3:20 PM, Ingo Molnar wrote: >> * Li Zhijian <lizhij...@cn.fujitsu.com> wrote: >> >>>> If the kernel initrd creation process creates an initrd which >>>> is larger than 2GB and also claims that it can't be placed >>>> with any part of it above 2GB, then that sounds like a bug >>>> in the initrd creation process... >>> Exactly, it's a real problem. >>> >>> Add x86 maintainers and LKML: >>> >>> The background is that QEMU want to support up to 4G initrd. but >>> linux header ( >>> initrd_addr_max field) only allow 2G-1. >>> Is one of the below approaches reasonable: >>> 1) change initrd_addr_max to 4G-1 directly >>> simply(arch/x86/boot/header.S)? >>> 2) lie QEMU bootloader the initrd_addr_max is 4G-1 even though header >>> said 2G-1 >>> 3) any else >> A 10 years old comment from hpa says: >> >> initrd_addr_max: .long 0x7fffffff >> # (Header version 0x0203 or >> later) >> # The highest safe address for >> # the contents of an initrd >> # The current kernel allows >> up to 4 GB, >> # but leave it at 2 GB to avoid >> # possible bootloader bugs. >> >> To avoid the potential of bugs lurking in dozens of major and hundreds of >> minor iterations of various Linux bootloaders I'd prefer a real solution >> and extend it - because if there's a 2GB initrd for some weird reason >> today there might be a 4GB one in two years. > > thank a lots. that's amazing. > > >> >> The real solution would be to: >> >> - Extend the boot protocol with a 64-bit field, named initrd_addr64_max >> or such. >> - We don't change the old field - but if the new field is set by new >> kernels then new bootloaders can use that as a new initrd_addr64_max >> value. (or reject to load the kernel if the address is too high.) >> >> - The kernel build should also emit a warning when building larger than >> 2GB initrds, with a list of bootloaders that support the new >> protocol. > > Actually i just knew QEMU(Seabios + optionrom(linuxboot_dma.bin)) can > support ~4GB initrd so far. > > i just drafted at patch to add this field. could you have a look. > another patch which is to document initrd_addr64_max is ongoing. > > commit db463ac9c1975f115d1ce2acb82d530c2b63b888 > Author: Li Zhijian <lizhij...@cn.fujitsu.com> > Date: Fri Nov 9 17:24:14 2018 +0800 > > x86: Add header field initrd_addr64_max > Years ago, kernel had support load ~4GB initrd. But for some > weird reasons ( > avoid possible bootloader bugs), it only allow leave initrd under > 2GB address > space(see initrd_addr_max fild at arch/x86/boot/header.S). > So modern bootloaders have not chance to load >=2G initrd > previously. > To avoid the potential of bugs lurking in dozens of major and > hundreds of > minor iterations of various Linux bootloaders. Ingo suggests to add > a new field > initrd_addr64_max. If bootloader believes that it can load initrd to >>=2G > address space, it can use initrd_addr64_max as the maximum loading > address in > stead of the old field initrd_addr_max. > > diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S > index 4c881c8..5fc3ebe 100644 > --- a/arch/x86/boot/header.S > +++ b/arch/x86/boot/header.S > @@ -300,7 +300,7 @@ _start: > # Part 2 of the header, from the old setup.S > > .ascii "HdrS" # header signature > - .word 0x020e # header version number (>= 0x0105) > + .word 0x020f # header version number (>= 0x0105) > # or else old loadlin-1.5 will > fail) > .globl realmode_swtch > realmode_swtch: .word 0, 0 # default_switch, SETUPSEG > @@ -562,6 +562,12 @@ acpi_rsdp_addr: .quad 0 > # 64-bit physical pointer to the > # ACPI RSDP table, added > with > # version 2.14 > > +#ifdef CONFIG_INITRD_SIZE_4GB > +initrd_addr64_max: .quad 0xffffffff # allow ~4G initrd since > 2.15 > +#else > +initrd_addr64_max: .quad 0
Shouldn't this be 0x7fffffff? And please update Documentation/x86/boot.txt Juergen
