Re: debian stretch dom0 + xen 4.9 fails to boot

From: Paul Durrant <Paul.Durrant@citrix.com>
To: 'Jan Beulich' <JBeulich@suse.com>
Cc: "xen-devel (xen-devel@lists.xenproject.org)"
	<xen-devel@lists.xenproject.org>
Subject: Re: debian stretch dom0 + xen 4.9 fails to boot
Date: Tue, 6 Jun 2017 15:51:40 +0000	[thread overview]
Message-ID: <fe6a9bb5eb8144bda27ef1532a153ab7@AMSPEX02CL03.citrite.net> (raw)
In-Reply-To: <5936E230020000780015FEDC@prv-mh.provo.novell.com>

> -----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.

  Paul

> Jan

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