linux-kernel - Re: 4.17.x won't boot due to "x86/boot/compressed/64: Handle 5-level paging boot if kernel is above 4G"

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Date:   Thu, 26 Jul 2018 18:21:11 +0200
From:   Dmitry Malkin <d.malkin@...l-time-systems.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     linux-x86_64@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: 4.17.x won't boot due to "x86/boot/compressed/64: Handle 5-level
 paging boot if kernel is above 4G"

On 07/26/2018 04:50 PM, Kirill A. Shutemov wrote:
>>>> 2. reading from memory which may be reserved in case of EFI systems:
>>>>>>      ebda_start = *(unsigned short *)0x40e << 4;
>>>>>>      bios_start = *(unsigned short *)0x413 << 10;
>>>> Also, on EFI system without CSM it will results in all zeros. Which will
>>>> place trampoline_start to 0x9d000. And it also may be reserved memory. In
>>>> fact I have such system and it is causes instant reboot (when code starts
>>>> copying to "trampoline_start").
>>> Could you show dmesg from such system?
>> Sure, here it is (please note than not both pages are reserved but only
>> second one: 0x9e000-0x9ffff):
> Well. That's bad.
>
> I don't see much options but parse e820 in decompression code. I hoped to
> avoid this.
>
> Let me see what I can do there.
Just in case of UEFI (I don't know much about BIOS and kexec):
register RSI (right before call paging_prepare) will contains pointer to 
"struct boot_params" (returned by function efi_main() in eboot.c).
There are fields e820_table and e820_entries.