[PATCH] kexec: Add --lite option

[Vivek Goyal]

On Thu, Oct 22, 2015 at 11:57:20AM -0700, Geoff Levand wrote:
> Hi Dave,
> 
> On Thu, 2015-10-22 at 11:17 +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.
> 
> As stated, this is not intended for use by kdump.
> 
> This is an optional feature.  It does not remove the integrity
> checks, but provides the user a way to bypass them if they so
> desire.

Why would somebody like to bypass these checks?

> 
> > > It was reported that on some systems where purgatory is running
> > > without caches enabled the sha256 calculations would take several
> > > minutes.  For bootloaders that just load a new image and
> > > immediately jump into it the loss of the integrity check is worth
> > > the increase in boot speed.  Please consider.  
> > 
> > Pratyush reported the arm64 issue, he sent a patch to fix it with
> > enabling cache for purgatory. I think the patch can fix the problem.
> > Why not fix it? The fix is simple enough and it does not introduce
> > complicate logic.
> 
> This patch also is simple, and is architecture independent.  I see this
> feature as an improvement to kexec, not necessarily as a fix for that
> problem.

I am not sure why does somebody care if segments are being checked
during transition or not?

Thanks
Vivek