Messages in this thread | | | Subject | Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd | From | Li Zhijian <> | Date | Fri, 9 Nov 2018 21:11:17 +0800 |
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Just noticed that there is a field xloadflags at recent protocol 60 Protocol 2.12: (Kernel 3.8) Added the xloadflags field and extension fields 61 to struct boot_params for loading bzImage and ramdisk 62 above 4G in 64bit. [snip] 617 Field name: xloadflags 618 Type: read 619 Offset/size: 0x236/2 620 Protocol: 2.12+ 621 622 This field is a bitmask. 623 624 Bit 0 (read): XLF_KERNEL_64 625 - If 1, this kernel has the legacy 64-bit entry point at 0x200. 626 627 Bit 1 (read): XLF_CAN_BE_LOADED_ABOVE_4G 628 - If 1, kernel/boot_params/cmdline/ramdisk can be above 4G. 629
maybe we can reuse this field and append a new Bit 5 XLF_INITRD_SIZE_4G or such
thanks Zhijian
On 11/9/2018 6:04 PM, Juergen Gross wrote: > On 09/11/2018 10:57, Li Zhijian wrote: >> On 11/9/2018 3:20 PM, Ingo Molnar wrote: >>> * Li Zhijian <lizhijian@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 <lizhijian@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
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