On Wed, Jan 26, 2011 at 01:58:13PM +0100, Ingo Molnar wrote: > > * Ahmed S. Darwish <darwish.07 at gmail.com> wrote: > > > - The latest approach (proposed by Linus) is to forget the disk: jump to > > real-mode, but display the kernel log in a fancy format (with scroll > > ups and downs) instead. > > > > Will re-initializing the VGA registers to their POST state be possible? > > If not, what about a "fail-safe" VGA driver? > > > > I'm most likely going to implement either the second or the third point, > > so I'd really appreciate some input. > > The third one suggested by Linus is the most useful and most direct one IMO. Such a > 'oops mode' screen would be useful for regular kernel crashes as well. > Yes, it is the safest approach. If I can make kexec and kdump work on early panics using some help from bootloaders though, that can possibly give us the feature of saving kernel logs to disk upon panics _without_ danger. I did not look at the kexec and kdump code bases yet, so this might be a pipe dream (respective developers are CCed -- input appreciated). > > 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'll investigate this further though. thanks, -- Darwish http://darwish.07.googlepages.com
