Re: Patch "x86/xen: Support kexec/kdump in HVM guests by doing a soft reset" has been added to the 4.2-stable tree

[Luis Henriques <luis.henriques@canonical.com>]

On Wed, Oct 14, 2015 at 08:24:50AM -0700, Greg Kroah-Hartman wrote:
> On Wed, Oct 14, 2015 at 04:20:16PM +0100, David Vrabel wrote:
> > On 13/10/15 23:59, gregkh@linuxfoundation.org wrote:
> > > 
> > > This is a note to let you know that I've just added the patch titled
> > > 
> > >     x86/xen: Support kexec/kdump in HVM guests by doing a soft reset
> > > 
> > > to the 4.2-stable tree which can be found at:
> > >     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> > > 
> > > The filename of the patch is:
> > >      x86-xen-support-kexec-kdump-in-hvm-guests-by-doing-a-soft-reset.patch
> > > and it can be found in the queue-4.2 subdirectory.
> > > 
> > > If you, or anyone else, feels it should not be added to the stable tree,
> > > please let <stable@vger.kernel.org> know about it.
> > > 
> > > 
> > > From 0b34a166f291d255755be46e43ed5497cdd194f2 Mon Sep 17 00:00:00 2001
> > > From: Vitaly Kuznetsov <vkuznets@redhat.com>
> > > Date: Fri, 25 Sep 2015 11:59:52 +0200
> > > Subject: x86/xen: Support kexec/kdump in HVM guests by doing a soft reset
> > > 
> > > From: Vitaly Kuznetsov <vkuznets@redhat.com>
> > > 
> > > commit 0b34a166f291d255755be46e43ed5497cdd194f2 upstream.
> > > 
> > > Currently there is a number of issues preventing PVHVM Xen guests from
> > > doing successful kexec/kdump:
> > > 
> > >   - Bound event channels.
> > >   - Registered vcpu_info.
> > >   - PIRQ/emuirq mappings.
> > >   - shared_info frame after XENMAPSPACE_shared_info operation.
> > >   - Active grant mappings.
> > > 
> > > Basically, newly booted kernel stumbles upon already set up Xen
> > > interfaces and there is no way to reestablish them. In Xen-4.7 a new
> > > feature called 'soft reset' is coming. A guest performing kexec/kdump
> > > operation is supposed to call SCHEDOP_shutdown hypercall with
> > > SHUTDOWN_soft_reset reason before jumping to new kernel. Hypervisor
> > > (with some help from toolstack) will do full domain cleanup (but
> > > keeping its memory and vCPU contexts intact) returning the guest to
> > > the state it had when it was first booted and thus allowing it to
> > > start over.
> > > 
> > > Doing SHUTDOWN_soft_reset on Xen hypervisors which don't support it is
> > > probably OK as by default all unknown shutdown reasons cause domain
> > > destroy with a message in toolstack log: 'Unknown shutdown reason code
> > > 5. Destroying domain.'  which gives a clue to what the problem is and
> > > eliminates false expectations.
> > [...]
> > > --- a/arch/x86/xen/enlighten.c
> > > +++ b/arch/x86/xen/enlighten.c
> > > @@ -33,6 +33,10 @@
> > >  #include <linux/memblock.h>
> > >  #include <linux/edd.h>
> > >  
> > > +#ifdef CONFIG_KEXEC_CORE
> > > +#include <linux/kexec.h>
> > > +#endif
> > > +
> > >  #include <xen/xen.h>
> > >  #include <xen/events.h>
> > >  #include <xen/interface/xen.h>
> > > @@ -1800,6 +1804,21 @@ static struct notifier_block xen_hvm_cpu
> > >  	.notifier_call	= xen_hvm_cpu_notify,
> > >  };
> > >  
> > > +#ifdef CONFIG_KEXEC_CORE
> > 
> > This should be CONFIG_KEXEC in 4.2 and earlier, CONFIG_EXEC_CORE was
> > introduced in 4.3.
> > 
> > Do you want an updated patch?
> 
> An updated patch would be great, thanks.

I'm queuing this patch changing CONFIG_KEXEC_CORE by CONFIG_KEXEC, as
suggested.  Thanks!

Greg, looks like several stable kernels have been released with this
bogus patch.

Cheers,
--
Lu�s