From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH 5/5] Fix kdump under KVM.
Date: Wed, 28 Oct 2009 10:41:00 -0200
Message-ID: <20091028124100.GA3063@amt.cnet>
References: <1256661667-9298-1-git-send-email-clalance@redhat.com> <1256661667-9298-6-git-send-email-clalance@redhat.com> <20091027174246.GA10473@amt.cnet> <4AE81B36.5010104@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: kvm@vger.kernel.org
To: Chris Lalancette <clalance@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:58991 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751763AbZJ1MmK (ORCPT <rfc822;kvm@vger.kernel.org>);
	Wed, 28 Oct 2009 08:42:10 -0400
Received: from int-mx03.intmail.prod.int.phx2.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.16])
	by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id n9SCgFZ4017169
	for <kvm@vger.kernel.org>; Wed, 28 Oct 2009 08:42:15 -0400
Content-Disposition: inline
In-Reply-To: <4AE81B36.5010104@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Wed, Oct 28, 2009 at 11:21:42AM +0100, Chris Lalancette wrote:
> Marcelo Tosatti wrote:
> > On Tue, Oct 27, 2009 at 05:41:07PM +0100, Chris Lalancette wrote:
> >> This patch is the main point of the series.  In order for
> >> kdump to properly work inside a KVM guest, we need to make
> >> sure that all VCPUs in virtual wire APIC mode get kicked
> >> to try and pick up the timer interrupts.  To do this,
> >> we iterate over the CPUs and deliver interrupts to the
> >> proper VCPUs.
> >>
> >> I don't love the concept of doing kvm_irq_kick_vcpus() from
> >> within pit_timer_fn().  A PIT is not connected to a CPU at all,
> >> only to a PIC or APIC.  However, if a CPU enters idle, this is
> >> the only way to wake it up to check for the interrupt.
> > 
> > The reason the PIT interrupt was fixed to BSP is:
> > 
> > http://www.mail-archive.com/kvm-devel@lists.sourceforge.net/msg13250.html
> > 
> > Perhaps enhancing ioapic_deliver's (irq == 0) check to bypass the       
> > destination overwrite in case its programmed by the guest to 
> > a single CPU would fix it?
> 
> Ug, nasty.  I definitely don't want to re-introduce that bug.  What exactly do
> you mean by "fix it"?  Do you mean fix the original RHEL-5.1 PAE issue, or fix
> the kdump issue?

The kdump issue. Something like:

#ifdef CONFIG_X86
        /* Always delivery PIT interrupt to vcpu 0 */
        if (irq == 0 && dest_multiple_vcpus(entry)) {
                irqe.dest_mode = 0; /* Physical mode. */
                /* need to read apic_id from apic regiest since
                 * it can be rewritten */
                irqe.dest_id = ioapic->kvm->bsp_vcpu->vcpu_id;
        }
#endif

The rest of the code should be ready to deal with it.