Re: [PATCH] x86: wrap kexec feature with CONFIG_KEXEC

[Ian Campbell <ian.campbell@citrix.com>]

On Thu, 2015-08-27 at 10:44 -0500, Jonathan Creekmore wrote:
> > 
> > On Aug 27, 2015, at 10:27 AM, David Vrabel <david.vrabel@citrix.com> 
> > wrote:
> > 
> > On 27/08/15 15:47, Jonathan Creekmore wrote:
> > > Add the appropriate #if checks around the kexec code in the x86 
> > > codebase
> > > so that the feature can actually be turned off by the flag instead of
> > > always required to be enabled on x86.
> > 
> > What's your use case for this?
> > 
> 
> The use case is for a slimmed down version of the hypervisor that can be 
> used as a security hypervisor, exposing as little extra functionality as 
> possible. When looking for features to trim out to reduce the attack 
> surface, I saw the flag for KEXEC and wanted to disable that, then ran 
> into compile problems.

Can this not be achieved at runtime with XSM?

In general (i.e. not 100% consistently, I think) we have tended to avoid
making things user-facing compile time options. Many of the existing
CONFIG_* and HAVE_* are really about things which are arch dependent, or
require specific porting to each arch etc. I think the KEXEC flag is one of
those.

This keeps the test matrix more reasonable (unlike e.g. Linux's Kconfig)
and also helps us by ensuring that users are mostly running one of a small
number of possible configs.

I slightly fear that after Kexec you are going to want to strip out more
and more stuff...

Ian.