linux-kernel - Re: s390 qemu boot failure in -next

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Date:   Mon, 25 Jun 2018 17:09:17 +0200
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Guenter Roeck <linux@...ck-us.net>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, qemu-s390x <qemu-s390x@...gnu.org>,
        qemu-devel <qemu-devel@...gnu.org>,
        Thomas Huth <thuth@...hat.com>
Subject: Re: s390 qemu boot failure in -next

On Mon, Jun 25, 2018 at 06:35:30AM -0700, Guenter Roeck wrote:
> On 06/25/2018 05:26 AM, Christian Borntraeger wrote:
> > 
> > 
> > On 06/25/2018 10:49 AM, Cornelia Huck wrote:
> > > On Mon, 25 Jun 2018 10:36:33 +0200
> > > Vasily Gorbik <gor@...ux.ibm.com> wrote:
> > > 
> > > > This change has been done on purpose. Uncompressed image is not going
> > > > to be bootable any more. In future the decompressor phase would get
> > > > more function (early memory detection as an example) and there is no
> > > > chance to duplicate that code in uncompressed image as well (to keep it
> > > > bootable on its own). The patch series commit messages contain more
> > > > technical details.
> > > > 
> > > > For qemu either bzImage or arch/s390/boot/compressed/vmlinux should be
> > > > used, which are bootable images.
> > > > 
> > > > But that's really confusing that uncompressed vmlinux is still kind
> > > > of booting. May be we should discuss how to avoid this confusion
> > > > (may be change uncompressed image enty point to a function doing
> > > > disabled wait with badb007 or smth) and how to encourage people to use
> > > > arch/s390/boot/compressed/vmlinux instead.
> > > 
> 
> If an image is not expected to be bootable, a message such as "This image does
> not boot. Please use <correct image>" would be nice. Unfortunately, which image
> to boot under qemu is pretty much undocumented, and it is guesswork for each
> architecture/platform.
> 
> Guenter
> 
> > I talked to Vasily and the vmlinux file in the linux source path is just an
> > intermediate file. Future changes will happen that will make that ELF file
> > unsuitable for direct boot anyway (e.g. think about potential ASLR or Kasan
> > changes).
> > 
> >   If yes, it would make sense to explicitly fence it. But I'm
> > > worried that it would break previously working setups (did we document
> > > the purpose of the images anywhere?
> > > 

To avoid confusion with trying to boot uncompressed vmlinux under qemu
we could detect it and print "nice" message in the kernel.

Please consider the following patch.

Vasily Gorbik (1):
  s390/boot: block uncompressed vmlinux booting attempts

 arch/s390/boot/head.S         |  4 ++--
 arch/s390/include/asm/setup.h |  3 ++-
 arch/s390/kernel/early.c      | 12 ++++++++++++
 3 files changed, 16 insertions(+), 3 deletions(-)

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