Re: s390 qemu boot failure in -next

From: Vasily Gorbik
Date: Mon Jun 25 2018 - 11:09:49 EST


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@xxxxxxxxxxxxx> 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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