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

[Dmitry Malkin]

On 07/26/2018 04:50 PM, Kirill A. Shutemov wrote:
> > > > 2. reading from memory which may be reserved in case of EFI systems:
> > > > > >   ÂÂ ebda_start = *(unsigned short *)0x40e << 4;
> > > > > >   ÂÂ 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.