From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from terminus.zytor.com ([2001:1868:205::10] helo=mail.zytor.com) by casper.infradead.org with esmtps (Exim 4.76 #1 (Red Hat Linux)) id 1TQKT8-0000Zf-7p for kexec@lists.infradead.org; Mon, 22 Oct 2012 16:03:13 +0000 Message-ID: <50856DFE.8000601@zytor.com> Date: Mon, 22 Oct 2012 09:02:06 -0700 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: [PATCH v1 0/2] x86, apic: Disable BSP if boot cpu is AP References: <3E5A0FA7E9CA944F9D5414FEC6C7122030B0DD68@ORSMSX105.amr.corp.intel.com> <20121016.140313.279437418.d.hatayama@jp.fujitsu.com> <3E5A0FA7E9CA944F9D5414FEC6C7122030B0DD91@ORSMSX105.amr.corp.intel.com> <20121016.153817.42643171.d.hatayama@jp.fujitsu.com> In-Reply-To: <20121016.153817.42643171.d.hatayama@jp.fujitsu.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: kexec-bounces@lists.infradead.org Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: HATAYAMA Daisuke Cc: fenghua.yu@intel.com, len.brown@intel.com, x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, rob.herring@calxeda.com, grant.likely@secretlab.ca, ebiederm@xmission.com, mingo@elte.hu, tglx@linutronix.de, vgoyal@redhat.com On 10/15/2012 11:38 PM, HATAYAMA Daisuke wrote: > > Thanks for pointing out this. And I've recalled my investigation in > the past now. So I want to stop retrying your patch v9 now. This NMI > method is definitely not applicable to 2nd kernel without any change. > > Your NMI method assumes BSP thread is halting in play dead loop. But > on the 2nd kernel, BSP is halting in the 1st kernel (or possibly in a > fatail system error). Even if throwing NMI to BSP, it goes back to the > 1st kernel soon again. I at least confirmed NMI handler is executed in > this case. > > Also, throwing NMI changes stack in the 1st kernel, which is > unpermissible from kdump's perspective. But x86_64 uses Interrupt > Stack Table (IST), in which stack switching is not performed. So 2nd > kernel's stack is used at least on x86_64. > > To sum up, to apply NMI method in the 2nd kernel, I think it necessary > to modify contexts pushed on the stack so execution goes to the 2nd > kernel's start_secondary() while initializing its state > appropreately. > > Also I think it necessary to discuss whether this NMI method is > reliable enough for kdump use. > I think it's pretty clear it is *not*. NMI or monitor would either have to rely on context set up by the first kernel, which simply isn't safe. Out of those two options, a monitor would actually be safer, since it can be self-contained in a completely different way. However, it seems that running on N-1 CPUs in kdump is perfectly acceptable. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec