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Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to a
From: |
Juergen Gross |
Subject: |
Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd |
Date: |
Fri, 9 Nov 2018 11:04:19 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 |
On 09/11/2018 10:57, Li Zhijian wrote:
> On 11/9/2018 3:20 PM, Ingo Molnar wrote:
>> * Li Zhijian <address@hidden> 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 <address@hidden>
> 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
- [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, (continued)
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, Peter Maydell, 2018/11/08
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, Li Zhijian, 2018/11/08
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, Ingo Molnar, 2018/11/09
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, Li Zhijian, 2018/11/09
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd,
Juergen Gross <=
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, Li Zhijian, 2018/11/09
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, Li Zhijian, 2018/11/09
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, H. Peter Anvin, 2018/11/09
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, Ingo Molnar, 2018/11/12
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, H. Peter Anvin, 2018/11/12
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, Ingo Molnar, 2018/11/12
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, H. Peter Anvin, 2018/11/12
- Re: [Qemu-devel] [RFC/PoC PATCH 1/3] i386: set initrd_max to 4G - 1 to allow up to 4G initrd, H. Peter Anvin, 2018/11/12
Re: [Qemu-devel] [RFC/PoC PATCH 0/3] support initrd size up to 4G, Wainer dos Santos Moschetta, 2018/11/08