From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx3.mail.elte.hu ([157.181.1.138]) by bombadil.infradead.org with esmtps (Exim 4.68 #1 (Red Hat Linux)) id 1JN5ne-0007to-HJ for kexec@lists.infradead.org; Thu, 07 Feb 2008 12:24:25 +0000 Date: Thu, 7 Feb 2008 13:24:04 +0100 From: Ingo Molnar Subject: Re: [PATCH], issue EOI to APIC prior to calling crash_kexec in die_nmi path Message-ID: <20080207122404.GA8195@elte.hu> References: <20080206192555.GA24910@hmsendeavour.rdu.redhat.com> <20080206220001.GA15155@elte.hu> <20080206224805.GD11886@redhat.com> <47AA3B16.7000507@zytor.com> <20080206233657.GB12393@elte.hu> <20080207121719.GA29279@hmsreliant.think-freely.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20080207121719.GA29279@hmsreliant.think-freely.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: kexec-bounces@lists.infradead.org Errors-To: kexec-bounces+dwmw2=infradead.org+dwmw2=infradead.org@lists.infradead.org To: Neil Horman Cc: kexec@lists.infradead.org, linux-kernel@vger.kernel.org, mingo@redhat.com, "Eric W. Biederman" , "H. Peter Anvin" , tglx@linutronix.de, Vivek Goyal * Neil Horman wrote: > Ingo noted a few posts down the nmi_exit doesn't actually write to the > APIC EOI register, so yeah, I agree, its bogus (and I apologize, I > should have checked that more carefully). Nevertheless, this patch > consistently allowed a hangning machine to boot through an Nmi lockup. > So I'm forced to wonder whats going on then that this patch helps > with. perhaps its a just a very fragile timing issue, I'll need to > look more closely. try a dummy iret, something like: asm volatile ("pushf; push $1f; iret; 1: \n"); to get the CPU out of its 'nested NMI' state. (totally untested) the idea is to push down an iret frame to the kernel stack that will just jump to the next instruction and gets it out of the NMI nesting. Note: interrupts will/must still be disabled, despite the iret. (the ordering of the pushes might be wrong, we might need more than that for a valid iret, etc. etc.) Ingo _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec