Re: [PATCH 1/4] x86/cpufeature: Add User-Mode Instruction Prevention definitions

[Ricardo Neri]

On Thu, 2016-11-10 at 09:58 +0100, Borislav Petkov wrote:
> On Wed, Nov 09, 2016 at 07:24:43PM -0800, Ricardo Neri wrote:
> > I intended this feature to be configurable at build time in case someone
> > wants to build a kernel without it; similar to other features such as
> > SMAP. Is this not needed? Should Linux be built with this feature always
> > enabled?
> > 
> > This feature could always be disabled via a kernel parameter, though;
> > even if Linux is built with it.
> 
> It probably is a good idea to have it build-time configurable for the
> embedded folks. But you can do a before and after build and look at
> the vmlinux size and see how much it has grown. If it is only a couple
> of KBs I guess we can drop the config option even but I know there are
> people who still care about KBs too...

Thanks for the suggestions. Perhaps I can include these metrics in my
V2. On th other hand, Dave Hansen gave a good argument on potential
conflicts when, of instance running on an AMD CPU. UMIP is enabled by
setting a bit in CR4. If that bit is not supposed to be set, that could
cause a #GP fault.

Thanks and BR,
Ricardo
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> SUSE Linux GmbH, GF: Felix ImendÃrffer, Jane Smithard, Graham Norton, HRB 21284 (AG NÃrnberg)