Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756847Ab2KZRnY (ORCPT ); Mon, 26 Nov 2012 12:43:24 -0500 Received: from out01.mta.xmission.com ([166.70.13.231]:56853 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755372Ab2KZRnT (ORCPT ); Mon, 26 Nov 2012 12:43:19 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Gleb Natapov Cc: Zhang Yanfei , "x86\@kernel.org" , "kexec\@lists.infradead.org" , Marcelo Tosatti , "linux-kernel\@vger.kernel.org" , "kvm\@vger.kernel.org" References: <50ADE0C2.1000106@cn.fujitsu.com> <50ADE11A.401@cn.fujitsu.com> <87ip8sxuyh.fsf@xmission.com> <20121126172054.GF12969@redhat.com> Date: Mon, 26 Nov 2012 11:43:10 -0600 In-Reply-To: <20121126172054.GF12969@redhat.com> (Gleb Natapov's message of "Mon, 26 Nov 2012 19:20:54 +0200") Message-ID: <87fw3wuuoh.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-AID: U2FsdGVkX1+6sYb8jVOP/s+rKXMZ+JMphrUGGGDxReA= X-SA-Exim-Connect-IP: 75.135.205.0 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 TVD_RCVD_IP TVD_RCVD_IP * 0.1 XMSubLong Long Subject * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa02 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_XMDrugObfuBody_08 obfuscated drug references X-Spam-DCC: XMission; sa02 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Gleb Natapov X-Spam-Relay-Country: Subject: Re: [PATCH v8 1/2] x86/kexec: add a new atomic notifier list for kdump X-SA-Exim-Version: 4.2.1 (built Sun, 08 Jan 2012 03:05:19 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1788 Lines: 40 Gleb Natapov writes: > On Mon, Nov 26, 2012 at 09:08:54AM -0600, Eric W. Biederman wrote: >> Zhang Yanfei writes: >> >> > This patch adds an atomic notifier list named crash_notifier_list. >> > Currently, when loading kvm-intel module, a notifier will be registered >> > in the list to enable vmcss loaded on all cpus to be VMCLEAR'd if >> > needed. >> >> crash_notifier_list ick gag please no. Effectively this makes the kexec >> on panic code path undebuggable. >> >> Instead we need to use direct function calls to whatever you are doing. >> > The code walks linked list in kvm-intel module and calls vmclear on > whatever it finds there. Since the function have to resides in kvm-intel > module it cannot be called directly. Is callback pointer that is set > by kvm-intel more acceptable? Yes a specific callback function is more acceptable. Looking a little deeper vmclear_local_loaded_vmcss is not particularly acceptable. It is doing a lot of work that is unnecessary to save the virtual registers on the kexec on panic path. In fact I wonder if it might not just be easier to call vmcs_clear to a fixed per cpu buffer. Performing list walking in interrupt context without locking in vmclear_local_loaded vmcss looks a bit scary. Not that locking would make it any better, as locking would simply add one more way to deadlock the system. Only an rcu list walk is at all safe. A list walk that modifies the list as vmclear_local_loaded_vmcss does is definitely not safe. Eric -- 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/