[PATCH 0/2][concept RFC] x86: BIOS-save kernel log to disk upon panic

Ingo Molnar mingo at elte.hu
Wed Jan 26 09:00:30 EST 2011

* Ahmed S. Darwish <darwish.07 at gmail.com> wrote:

> > Also, have you tried BIOS warm reset vector, which is supposed to reboot without 
> > clearing RAM contents - how well does it work in practice on typical laptops? If 
> > on crash we could reboot without memory getting cleared that would open up a 
> > vast area of space to store the kernel log into (RAM).
> AFAIK, the lmode->rmode transition is more forward-compatible.
> It seems the only place warm boot was documented is in the Intel MP spec, a 
> 12-years old document long obsoleted by ACPI. Meanwhile, the real-mode transition 
> is rigorously documented in the current Intel and AMD manuals, albeit in kind of a 
> holier-than-thou approach.

I mean, use the warm reset vector to truly reset the box.

Then, once a stable known-good kernel boots, *that* kernel can then recover all the 
log data which is sitting in a well-known place in RAM, automatically and 

Basically a bit like kexec, just more convenient and it also goes through the BIOS 
warm reset, so it might work better than kexec ...



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