Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754667Ab3HIRRj (ORCPT ); Fri, 9 Aug 2013 13:17:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39802 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752335Ab3HIRRi (ORCPT ); Fri, 9 Aug 2013 13:17:38 -0400 Date: Fri, 9 Aug 2013 19:12:00 +0200 From: Oleg Nesterov To: Frederic Weisbecker Cc: Linus Torvalds , Grazvydas Ignotas , Felipe Contreras , Linux Kernel Mailing List , Ingo Molnar , Denys Vlasenko Subject: Re: [PATCH 0/1] (Was: Linux 3.11-rc4) Message-ID: <20130809171200.GA8901@redhat.com> References: <20130806154314.GA398@redhat.com> <20130807192734.GA8395@redhat.com> <20130808154107.GA28971@redhat.com> <20130808165427.GC32049@somewhere> <20130808181521.GA11138@redhat.com> <20130809164548.GD13339@somewhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130809164548.GD13339@somewhere> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2986 Lines: 79 On 08/09, Frederic Weisbecker wrote: > > On Thu, Aug 08, 2013 at 08:15:21PM +0200, Oleg Nesterov wrote: > > But probably we should move "attr.bp_len == HW_BREAKPOINT_LEN_1" check > > from arch_build_bp_info() to its caller, arch_validate_hwbkpt_settings(). > > > > Because: > > > > > But this bp_len > > > should rather be used for range breakpoints on archs that support it. > > > > Yes, exactly, and we already have the patches for amd, so bp->len can > > be actually != 1 but currently we can't support because it is checked > > in arch_build_bp_info(). > > Hmm, but how moving that to arch_validate_hwbkpt_seetings() would solve > the issue? Of course, this itself won't solve the issue, sorry for confusion. I meant that arch_build_bp_info(X86_BREAKPOINT_EXECUTE) should not fail if ->bp_len is wrong, just because (unless we add more complications) it can't know if it is correct or not (if the hardware supports the range EXECUTE bps). arch_validate_hwbkpt_settings() does the additional checks anyway, and more importantly it checks cpu_has_bpext/mask. So I think it should also have the additional check for X86_BREAKPOINT_EXECUTE case. > > @@ -265,15 +262,11 @@ static int arch_build_bp_info(struct per > > break; > > case HW_BREAKPOINT_X: > > info->type = X86_BREAKPOINT_EXECUTE; > > - /* > > - * x86 inst breakpoints need to have a specific undefined len. > > - * But we still need to check userspace is not trying to setup > > - * an unsupported length, to get a range breakpoint for example. > > - */ > > - if (bp->attr.bp_len == sizeof(long)) { > > - info->len = X86_BREAKPOINT_LEN_X; > > - return 0; > > - } > > + /* until we change tools/perf */ > > + if (bp->attr.bp_len == sizeof(long)) > > + bp->attr.bp_len = HW_BREAKPOINT_LEN_1; > > Too bad we need to keep that compatibility around. Yes, agreed... Do you see a better approach? And just in case, it is not that I think that this hack is much better than "ignore bp_len" as you suggested before. It's up to you. > Do you think this could be > a problem for AMD range breakpoints? Yes, this doesn't look exactly right if ->bp_len == 8 actually tries to denote a range. But this is the temporary hack, and at least currently info->mask is only used if len > LEN_8, so I hope this should be fine. > We can also fix the tools, then may be we'll be able to remove the kernel hack > compatibility in a few years. Or perhaps even earlier ;) And, perhaps after we change the tools we can add pr_warn() for this case. > Oh I need to check other archs as well. Yes, and I'm afraid that tools/perf needs some arch-dependant define for HW_BREAKPOINT_X's attr.bp_len. Or perhaps attr.bp_len == 0 could mean "choose the right length" ? Oleg. -- 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/