Re: [PATCH -next] init/main: Init jump_labels before they are used to build zonelists

[Stafford Horne]

On Tue, Jan 17, 2017 at 02:44:54PM +0100, Peter Zijlstra wrote:
> On Tue, Jan 17, 2017 at 02:07:36PM +0100, Vlastimil Babka wrote:
> 
> > Anyway I'm not sure if this patch is safe. Hopefully Peter can judge
> > this better...
> > 
> > > Cc: Vlastimil Babka <vbabka@xxxxxxx>
> > > Signed-off-by: Stafford Horne <shorne@xxxxxxxxx>
> > > ---
> > >  init/main.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > > 
> > > diff --git a/init/main.c b/init/main.c
> > > index 8b1adb6e..d1ca7cb 100644
> > > --- a/init/main.c
> > > +++ b/init/main.c
> > > @@ -513,6 +513,7 @@ asmlinkage __visible void __init start_kernel(void)
> > >  	boot_cpu_state_init();
> > >  	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
> > >  
> > > +	jump_label_init();
> > >  	build_all_zonelists(NULL, NULL);
> > >  	page_alloc_init();
> > >  
> > > @@ -526,8 +527,6 @@ asmlinkage __visible void __init start_kernel(void)
> > >  		parse_args("Setting init args", after_dashes, NULL, 0, -1, -1,
> > >  			   NULL, set_init_arg);
> > >  
> > > -	jump_label_init();
> > > -
> 
> Urgh, that means auditing all archs that implement this. The thing
> you're looking for is if the self-modifying code cruft can be done that
> early.
> 
> x86 looks to be fine, because this is after setup_arch() which is
> required for ideal_nops[] to be initialied and we use text_poke_early()
> which doesn't really need anything else.
> 
> I've not gone through the other arches...

Vlastimil,

Will you be able to look into that? Openrisc doesnt have jump_label
support, so its no issue at the moment.

Archs that do have it:

arch/arm64/Kconfig:     select HAVE_ARCH_JUMP_LABEL
arch/mips/Kconfig:      select HAVE_ARCH_JUMP_LABEL
arch/s390/Kconfig:      select HAVE_ARCH_JUMP_LABEL
arch/sparc/Kconfig:     select HAVE_ARCH_JUMP_LABEL if SPARC64
arch/tile/Kconfig:      select HAVE_ARCH_JUMP_LABEL
arch/x86/Kconfig:       select HAVE_ARCH_JUMP_LABEL
arch/arm/Kconfig:       select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU
arch/powerpc/Kconfig:   select HAVE_ARCH_JUMP_LABEL

I looked at a few (arm, tile) and I dont see their arch_jump_label_transform*
implementations depending on global state like ideal_nops from x86. They
should be ok.

If no time, Should you change your patch to not use static keys for
build_all_zonelists at least?