Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753250Ab3JFAMu (ORCPT ); Sat, 5 Oct 2013 20:12:50 -0400 Received: from order.stressinduktion.org ([87.106.68.36]:43139 "EHLO order.stressinduktion.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752494Ab3JFAMt (ORCPT ); Sat, 5 Oct 2013 20:12:49 -0400 Date: Sun, 6 Oct 2013 02:12:47 +0200 From: Hannes Frederic Sowa To: Steven Rostedt Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Jason Baron , Peter Zijlstra , Eric Dumazet , "David S. Miller" , x86@kernel.org Subject: Re: [PATCH net-next v2 3/8] x86/jump_label: expect default_nop if static_key gets enabled on boot-up Message-ID: <20131006001247.GB25076@order.stressinduktion.org> Mail-Followup-To: Steven Rostedt , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Jason Baron , Peter Zijlstra , Eric Dumazet , "David S. Miller" , x86@kernel.org References: <1381015258-7667-1-git-send-email-hannes@stressinduktion.org> <1381015258-7667-4-git-send-email-hannes@stressinduktion.org> <20131005200558.3be2f841@gandalf.local.home> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20131005200558.3be2f841@gandalf.local.home> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1703 Lines: 47 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/