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port-amd64/42645: Instant reboot with big modules (e.g. miniroot.kmod) on amd64
>Synopsis: Instant reboot with big modules (e.g. miniroot.kmod) on amd64
>Arrival-Date: Tue Jan 19 22:40:00 +0000 2010
>Originator: Vladimir 'phcoder' Serbinenko
>Release: 5.0.1 and -current
sys/arch/amd64/amd64/locore.S seems to map only pages in the range
0x100000-0x1800000 When total amount of loaded modules is higher than that
kernel instantly reboots (triple fault). It happes in following chunk of code:
* Finally, we're in long mode. However, we're still
* in the identity mapped area (could not jump out
* of that earlier because it would have been a > 32bit
* jump). We can do that now, so here we go.
* We have arrived.
* There's no need anymore for the identity mapping in low
* memory, remove it.
#if L2_SLOT_KERNBASE > 0
addq %r8, %rbx
1: movq $0,(%rbx)
More exactly on 1: movq $0,(%rbx)
It tries to remove some mappings but since page table is after modules if big
modules were loaded the memory holding pagetable isn't mapped. Triple fault.
Make a miniroot.kmod with 32MiB image. Load it in bootloader, type boot and see
how you get triple-fault reboot instead.
add necessary entries to initial pagetable. LAzy solution would be just to map
low 4GiB. Since boot protocol has 32-bit pointers this value can't be exceeded
and mapping with 2M pages should be quite easy
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