Re: [PATCH v2] ARM: initialize jump labels before setup_machine_fdt()

[Phil Elwell]

On 07/06/2022 16:44, Jason A. Donenfeld wrote:
> Hi Phil,
>
> On Tue, Jun 07, 2022 at 04:35:32PM +0100, Phil Elwell wrote:
> > Jason,
> >
> > On 07/06/2022 16:14, Jason A. Donenfeld wrote:
> > > Hey again,
> > >
> > > On Tue, Jun 07, 2022 at 10:15:27AM +0100, Phil Elwell wrote:
> > > > On 07/06/2022 09:43, Jason A. Donenfeld wrote:
> > > > > Hi Phil,
> > > > >
> > > > > On Tue, Jun 7, 2022 at 10:29 AM Phil Elwell <phil@xxxxxxxxxxxxxxx> wrote:
> > > > > > This patch is fatal for me in the downstream Raspberry Pi kernel - it locks up
> > > > > > on boot even before the earlycon output is available. Hacking jump_label_init to
> > > > > > skip the jump_entry for "crng_is_ready" allows it to boot, but is likely to have
> > > > > > consequences further down the line.
> > > > >
> > > > > Also, reading this a few times, I'm not 100% sure I understand what
> > > > > you did to hack around this and why that works. Think you could paste
> > > > > your hackpatch just out of interest to the discussion (but obviously
> > > > > not to be applied)?
> > > >
> > > > This is the minimal version of my workaround patch that at least allows the
> > > > board to boot. Bear in mind that it was written with no previous knowledge of
> > > > jump labels and was arrived at by iteratively bisecting the list of jump_labels
> > > > until the first dangerous one was found, then later working out that there was
> > > > only one.
> > >
> > > Looks like this patch fails due to CONFIG_STRICT_KERNEL_RWX.
> > > Investigating deeper now, but that for starters seems to be the
> > > differentiating factor between my prior test rig and one that reproduces
> > > the error. I assume your raspi also sets CONFIG_STRICT_KERNEL_RWX.
> >
> > Yes, it does, as does multi_v7_defconfig.
>
> Oh good. Adjusting my CI now to have that.
>
> Having tickled arch/arm/ a little bit now, this is looking sort of
> complicated. So I think I might be leaning toward giving up and just
> rolling with <https://git.zx2c4.com/linux-rng/commit/?id=78f79dda>.
>
> Unless of course somebody has some ARM chops and can think of a quick
> easy fix.

I've not looked at the performance implications (if any), but in terms of when the RNG initilialization completes and the lack of a WARN I'm happy with that patch, a.k.a. [1].

Phil

[1] https://lore.kernel.org/lkml/20220607100210.683136-1-Jason@xxxxxxxxx/