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Date: Sun, 6 Oct 2013 02:12:47 +0200 From: Hannes Frederic Sowa <hannes@...essinduktion.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Jason Baron <jbaron@...hat.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, x86@...nel.org Subject: Re: [PATCH net-next v2 3/8] x86/jump_label: expect default_nop if static_key gets enabled on boot-up On Sat, Oct 05, 2013 at 08:05:58PM -0400, Steven Rostedt wrote: > > if (type == JUMP_LABEL_ENABLE) { > > - /* > > - * We are enabling this jump label. If it is not a nop > > - * then something must have gone wrong. > > - */ > > - if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0)) > > - bug_at((void *)entry->code, __LINE__); > > + if (init) { > > + /* > > + * Jump label is enabled for the first time. > > + * So we expect a default_nop... > > + */ > > + if (unlikely(memcmp((void *)entry->code, default_nop, 5) > > + != 0)) > > + bug_at((void *)entry->code, __LINE__); > > + } else { > > + /* > > + * ...otherwise expect an ideal_nop. Otherwise > > + * something went horribly wrong. > > + */ > > + if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) > > + != 0)) > > + bug_at((void *)entry->code, __LINE__); > > + } > > I don't know if I like this change. This is similar to a bug we had > with the Xen folks, where they didn't realize that jump labels are not > suppose to be used (or set) before jump_label_init() is called. > > I'll have to take a deeper look at this on Monday. Yes, I understand and saw the commit to call jump_label_init earlier. Maybe the default could be to insert illegal instructions by default if we try to replace them with nops or branches afterwards anyway. insn_sanity programs would have to be tought about that, then. Greetings, Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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