Re: debian stretch dom0 + xen 4.9 fails to boot

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@lists.xen.org] On Behalf Of
> Paul Durrant
> Sent: 06 June 2017 16:52
> To: 'Jan Beulich' <JBeulich@suse.com>
> Cc: xen-devel (xen-devel@lists.xenproject.org) <xen-
> devel@lists.xenproject.org>
> Subject: Re: [Xen-devel] debian stretch dom0 + xen 4.9 fails to boot
> 
> > -----Original Message-----
> > From: Jan Beulich [mailto:JBeulich@suse.com]
> > Sent: 06 June 2017 16:11
> > To: Paul Durrant <Paul.Durrant@citrix.com>
> > Cc: xen-devel (xen-devel@lists.xenproject.org) <xen-
> > devel@lists.xenproject.org>
> > Subject: Re: [Xen-devel] debian stretch dom0 + xen 4.9 fails to boot
> >
> > >>> On 06.06.17 at 16:32, <Paul.Durrant@citrix.com> wrote:
> > > I've been having fun setting up a new test rig...
> > >
> > > I have a skull canyon NUC and I put debian stretch (rc4) on it (so that's a
> > > 4.9 kernel) and then tried building and installing the latest Xen staging-4.9
> > > code. The system failed to boot... basically it got stuck before even
> > > managing to get sufficiently into Xen to spit out anything on the console.
> > > Xen 4.8 OTOH booted just fine so I started bisecting and after 14
> iterations
> > > I got down to the following commit is being the problem:
> > >
> > > commit c0655e492e6b33e26ec9cd33f59725d0db89cdd0
> > > Author: Juergen Gross <jgross@suse.com>
> > > Date:   Fri Mar 24 14:18:54 2017 +0100
> > >
> > >     x86: split boot trampoline into permanent and temporary part
> > >
> > >     The hypervisor needs a trampoline in low memory for early boot and
> > >     later for bringing up cpus and during wakeup from suspend. Today this
> > >     trampoline is kept completely even if most of it isn't needed later.
> > >
> > >     Split the trampoline into a permanent part and a temporary part
> needed
> > >     at early boot only. Introduce a new entry at the boundary.
> > >
> > >     Reduce the stack for wakeup code in order for the permanent
> > >     trampoline to fit in a single page. 4k of stack seems excessive, about
> > >     3k should be more than enough.
> > >
> > >     Add an ASSERT() to the linker script to ensure the wakeup stack is
> > >     always at least 3k.
> > >
> > >     Signed-off-by: Juergen Gross <jgross@suse.com>
> > >     Reviewed-by: Jan Beulich <jbeulich@suse.com>
> > >
> > > To verify this I checked out master, reverted that commit, and tried again.
> > > The NUC still booted fine.
> >
> > Well, interesting, but I don't think it is very realistic to expect any
> > fix with just the information you supply. There must be something
> > rather special about that system, and likely it would help if we
> > knew what that is. E.g. an unusual E820 map. Worse would be if
> > they used memory outside of properly marked E820 regions in a
> > way colliding with what we do.
> >
> > Otherwise I'm afraid we need to hope for you to debug the issue.
> >
> 
> Yes, I was posting this more a heads-up for the moment, so that 4.9 does not
> go out with this regression.
> 
> I will try to figure out what is going on... My initial thoughts on looking at what
> the patch does are that it may be something to do with the fact I am using a
> vga console rather than a serial one. I need to try another 4.9 on another
> system (gigabyte brix) to see if the problem manifests there too. I'll also have
> to play with the BIOS settings on the skull canyon.
> 

The problem definitely doesn't manifest on the brix, so the next theory is that it is something to do with the BIOS of the skull canyon.

  Paul

>   Paul
> 
> > Jan
> 
> 
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