Re: [PATCH v1 2/8] s390/sclp: check sccb len before filling in data

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 12 May 2020 12:16:45 -0400
Collin Walling <walling@linux.ibm.com> wrote:

> On 5/12/20 12:01 PM, Cornelia Huck wrote:
> > On Mon, 11 May 2020 17:02:06 +0200
> > David Hildenbrand <david@redhat.com> wrote:
> >   
> >> On 11.05.20 16:50, Janosch Frank wrote:  
> >>> On 5/11/20 4:44 PM, David Hildenbrand wrote:  
> >>>> On 11.05.20 16:36, Janosch Frank wrote:  
> >>>>> On 5/9/20 1:08 AM, Collin Walling wrote:  
> >>>>>> The SCCB must be checked for a sufficient length before it is filled
> >>>>>> with any data. If the length is insufficient, then the SCLP command
> >>>>>> is suppressed and the proper response code is set in the SCCB header.
> >>>>>>
> >>>>>> Signed-off-by: Collin Walling <walling@linux.ibm.com>  
> >>>>>
> >>>>> Fixes tag?  
> > 
> > Probably
> > 
> > Fixes: 832be0d8a3bb ("s390x: sclp: Report insufficient SCCB length")
> > 
> > ?
> >   
> 
> Sounds reasonable. This patch doesn't fix any explicitly-known bugs 
> AFAIK. The s390 Linux kernel is hard-coded to use a 4K size SCCB when
> executing these commands.
> 
> I suppose this could introduce a bug if things change in the Linux 
> kernel or if some other OS wants to use this command. That should be 
> enough of a justification, right? (Just want to make sure I understand 
> the use of the tag correctly).

Yes; from the description of how this is supposed to work it fixes
architectural conformance, not a bug that is triggered by today's guest
systems.

[Usage of the Fixes: tag in QEMU is not quite as essential as in Linux,
as we don't do the numerous, big stable updates here; I don't think
this is stable material, but we can certainly record where this was
introduced.]