Re: [Qemu-devel] [PATCH] s390-ccw: Fix alignment for CCW1

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 29 Aug 2017 08:39:27 -0400
Farhan Ali <alifm@linux.vnet.ibm.com> wrote:

> On 08/29/2017 08:04 AM, Cornelia Huck wrote:
> > On Mon, 28 Aug 2017 10:28:53 -0400
> > Farhan Ali <alifm@linux.vnet.ibm.com> wrote:
> >  
> >> On 08/28/2017 10:19 AM, Halil Pasic wrote:  
> >>>
> >>>
> >>> On 08/28/2017 04:15 PM, Farhan Ali wrote:  
> >>>>
> >>>>
> >>>> On 08/28/2017 10:05 AM, Cornelia Huck wrote:  
> >>>>>>>> It's the alignment of the CCW which causes the problem.
> >>>>>>>>
> >>>>>>>> The exact error message when starting the guest was:
> >>>>>>>>
> >>>>>>>> ! No virtio device found !
> >>>>>>>>
> >>>>>>>> Since it worked for SCSI and CDL, and failed for LDL disks on that particular system, we are not really sure what caused the failure.
> >>>>>>>> Debugging it further showed the CCW for LDL disks were not aligned at double word boundary.  
> >>>>> This is really, really odd, as the low-level ccw code is the same for
> >>>>> any disk type...
> >>>>>  
> >>>> Exactly!
> >>>>  
> >>>>>>>> Trying the test on a different system with LDL disks worked fine, with the aligned(8) fix.  
> >>>>>>> Do you happen to have an old s390-ccw.img laying around in the test folder? QEMU might pick up
> >>>>>>> this one (e.g. when calling it without libvirt from the command line).
> >>>>>>>  
> >>>>>> I explicitly mention the bios to use with '-bios' option and pick up the
> >>>>>> latest bios. Without the aligned fix I see the error and with the fix it
> >>>>>> works fine.  
> >>>>> Wait, so the fix fixes it? Or am I confused now?
> >>>>>  
> >>>>
> >>>> It fixes in my system and one other system we tried on. But fails on a system where this issue was first noticed.  
> >>>
> >>> This is very confusing. So you have tried -bios on the system
> >>> where the issue was first noticed and the issue still persists
> >>> despite of the fixed bios is specified?
> >>>  
> >> Yes.
> >>
> >> The system where the issue was first noticed, applying the fix for the
> >> bios, fixes for:
> >>
> >> 1) CDL disks
> >> 2) SCSI disks
> >>
> >> But fails for LDL disk.
> >>
> >> On my system and one other system, the fix works for all the disk types,
> >> CDL, SCSI and LDL and fixes the issue.  
> >
> > Are you using different toolchains on the failing and the working
> > systems? Does it work when you copy the bios from a working system?
> >
> > (Clutching at straws here...)
> >  
> 
> So yesterday we realized for the failing system, the bios wasn't being 
> built on that system rather it was being built on a different system and 
> being copied over to the failing system. :/

Oh dear... the system it was built on hopefully was missing the fix,
right? (I'm getting a bit paranoid here.)

> 
> Building the bios on the failing system with the fix, resolves the issue 
> and we did not see anymore failures.
> So I think I can safely say this patch fixes the alignment problem.

Out of interest, which toolchain are you using? My rebuild is on F26.