Re: [PATCH] pc-bios: s390x: Only set lowcore iplb address on list-directed IPL

[Jason J. Herne]

On 8/17/20 12:30 PM, Cornelia Huck wrote:
> On Mon, 17 Aug 2020 10:17:34 -0400
> "Jason J. Herne" <jjherne@linux.ibm.com> wrote:
>
> > The POP states that the IPLB location is only written to 0x14 for
> > list-directed IPL. Some operating systems expect 0x14 to not change on
> > boot and will fail IPL if it does change.
> >
> > Fixes: 9bfc04f9ef6802fff0
>
> Should be
>
> Fixes: 9bfc04f9ef68 ("pc-bios: s390x: Save iplb location in lowcore")
>
> > Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
> > Reviewed-by: Janosch Frank <frankja@de.ibm.com>
> > ---
> >   pc-bios/s390-ccw/jump2ipl.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
> > index 767012bf0c..5e3e13f4b0 100644
> > --- a/pc-bios/s390-ccw/jump2ipl.c
> > +++ b/pc-bios/s390-ccw/jump2ipl.c
> > @@ -33,7 +33,10 @@ void jump_to_IPL_code(uint64_t address)
> >   {
> >       /* store the subsystem information _after_ the bootmap was loaded */
> >       write_subsystem_identification();
> > -    write_iplb_location();
> > +
> > +    if (iplb.pbt != S390_IPL_TYPE_CCW) {
> > +            write_iplb_location();
> > +    }
>
> What happens for ipl types other than CCW and FCP? IOW, should that
> rather be a positive check for S390_IPL_TYPE_FCP?
>
> >   
> >       /* prevent unknown IPL types in the guest */
> >       if (iplb.pbt == S390_IPL_TYPE_QEMU_SCSI) {

Based on my (admittedly limited) understanding of the architecture and
code, I believe write_iplb_location() should be called at least for
S390_IPL_TYPE_FCP but I'm not 100% sure on S390_IPL_TYPE_QEMU_SCSI.
Perhaps Janosch has an idea?

It was originally unconditional, and my new conditional excludes vfio
CCW which is definitely a step in the right direction, in any case :).


--
-- Jason J. Herne (jjherne@linux.ibm.com)