[PATCH] kexec: Add --lite option

[Scott Wood]

On Thu, 2015-10-22 at 12:08 -0700, Geoff Levand wrote:
> Hi Vivek,
> 
> On Thu, 2015-10-22 at 08:50 -0400, Vivek Goyal wrote:
> > On Thu, Oct 22, 2015 at 11:17:18AM +0800, Dave Young wrote:
> > > On 10/21/15 at 04:12pm, Geoff Levand wrote:
> > > > Add a new option --lite to kexec that allows for a fast reboot
> > > > by avoiding the purgatory integrity checks.  This option is
> > > > intended for use by kexec based bootloaders that load a new
> > > > image and then immediately transfer control to it.
> > > 
> > > I think Vivek was rejecting this --lite since kdump need the purgatory
> > > integrity checks. Ccing him.
> > 
> > Right. Why are we trying to bypass sha256 hash verification of loaded
> > segments at run time, that needs to be justified. 
> 
> Please see my reply to Dave.
> 
> > Atleast on x86, this integrity verification was fast and we did not
> > notice any siginificant delays in purgatory. And in that case extra knob
> > like this is hard to justify.
> 
> I notice the difference on the my arm64 system, so I guess we
> are even on that.

For me it was beyond "notice the difference" -- I thought it was completely 
broken, and was preparing to debug, until it started spitting out output over 
a minute later.

Compiling the sha256 code with -O2 instead of -O0 cut it down to around 10 
seconds (still unpleasant, but not quite as crazy... still unacceptable for 
non-kdump, though).  There was a patch posted a couple years ago to do that --
does anyone know what happened to it?

http://kexec.infradead.narkive.com/JSemzXoT/patch-purgatory-compile-sha256-c-only-on-ia64-with-o0

-Scott