Re: [PATCH 3/3] cpu-timers, icount: new modules

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 9 Jul 2020 20:46:56 +0200
Claudio Fontana <cfontana@suse.de> wrote:

> On 7/9/20 8:38 PM, Claudio Fontana wrote:
> > On 7/8/20 5:05 PM, Paolo Bonzini wrote:  
> >> On 08/07/20 17:00, Claudio Fontana wrote:  
> >>>> Bisectable, 100% failure rate, etc. :(  Can you split the patch in
> >>>> multiple parts, specifically separating any rename or introducing of
> >>>> includes from the final file move?  
> >>> Hi Paolo,
> >>>
> >>> will take a look!
> >>>
> >>> Is this captured by some travis / cirrus-ci / anything I can easily see the result of?
> >>>
> >>>  
> >>
> >> Nope, unfortunately we don't have an s390 CI.  But if you can get your
> >> hands on one, just "./configure --target-list=s390x-softmmu && make &&
> >> make check-block" will show it.  
> > 
> > So this is tricky, but I am making some progress after getting my hands on one.
> > Maybe if someone understands s390 keys better, I could be clued in.  
> 
> 
> Also adding Cornelia to Cc:.
> 
> Maybe the savevm_s390_storage_keys SaveVMHandlers etc assume that the icount state part of the vmstate is there?

I don't see anything that would deal with icount here. Adding Jason to
cc: in case he has an idea. (I assume it would behave the same under
KVM, as the only thing different are the internal callbacks.)

> 
> 
> > 
> > In short this goes away if I again set icount to enabled for qtest,
> > basically ensuring that --enable-tcg is there and then reenabling icount.
> > 
> > qtest was forcing icount and shift=0 by creating qemu options, in order to misuse its counter feature,
> > instead of using a separate counter.
> > 
> > Removing that ugliness we end up with different behavior of save/load, because vmstate will now suddenly not contain icount-related values anymore.
> > What I do not understand is why this causes a problem because save should just not store the icount state and load should just not load the icount state,
> > and why we die on the load of s390 keys state (it works just fine for other architectures).

Yes, I don't really see why skeys is so special. No endianness stuff, I
assume?

> > 
> > Here is a diff that makes the problem disappear, but needs --enable-tcg:
> > 
> > 
> > ----------------------------------------------------------------------------------------------------
> > diff --git a/accel/qtest.c b/accel/qtest.c
> > index 119d0f16a4..4cb16abc2c 100644
> > --- a/accel/qtest.c
> > +++ b/accel/qtest.c
> > @@ -23,6 +23,12 @@
> >  
> >  static int qtest_init_accel(MachineState *ms)
> >  {
> > +    QemuOpts *opts = qemu_opts_create(qemu_find_opts("icount"), NULL, 0,
> > +                                      &error_abort);
> > +    qemu_opt_set(opts, "shift", "0", &error_abort);
> > +    icount_configure(opts, &error_abort);
> > +    qemu_opts_del(opts);
> > +
> >      return 0;
> >  }
> >  
> > diff --git a/softmmu/vl.c b/softmmu/vl.c
> > index f39fd5270b..a5e788c86a 100644
> > --- a/softmmu/vl.c
> > +++ b/softmmu/vl.c
> > @@ -2786,10 +2786,12 @@ static void configure_accelerators(const char *progname)
> >          error_report("falling back to %s", ac->name);
> >      }
> >  
> > +    /*
> >      if (icount_enabled() && !tcg_enabled()) {
> >          error_report("-icount is not allowed with hardware virtualization");
> >          exit(1);
> >     }
> > +    */
> >  }
> >  
> >  static void create_default_memdev(MachineState *ms, const char *path)
> > ----------------------------------------------------------------------------------------------------
> > 
> > Without this patch, here is the full failure, maybe someone has a good hint, otherwise I'll keep digging from here inside the s390-specific code.
> > 
> > QA output created by 267
> > 
> > === No block devices at all ===
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing:
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > Error: No block device can accept snapshots
> > (qemu) info snapshots
> > No available block device supports snapshots
> > (qemu) loadvm snap0
> > Error: No block device supports snapshots
> > (qemu) quit
> > 
> > 
> > === -drive if=none ===
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing: -drive driver=file,file=TEST_DIR/t.IMGFMT,if=none
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > Error: Device 'none0' is writable but does not support snapshots
> > (qemu) info snapshots
> > No available block device supports snapshots
> > (qemu) loadvm snap0
> > Error: Device 'none0' is writable but does not support snapshots
> > (qemu) quit
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing: -drive driver=IMGFMT,file=TEST_DIR/t.IMGFMT,if=none
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > (qemu) info snapshots
> > List of snapshots present on all disks:
> > ID        TAG                     VM SIZE                DATE       VM CLOCK
> > --        snap0                      SIZE yyyy-mm-dd hh:mm:ss   00:00:00.000
> > (qemu) loadvm snap0
> > (qemu) quit
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing: -drive driver=IMGFMT,file=TEST_DIR/t.IMGFMT,if=none -device virtio-blk,drive=none0
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > (qemu) info snapshots
> > List of snapshots present on all disks:
> > ID        TAG                     VM SIZE                DATE       VM CLOCK
> > --        snap0                      SIZE yyyy-mm-dd hh:mm:ss   00:00:00.000
> > (qemu) loadvm snap0
> > (qemu) quit
> > 
> > 
> > === -drive if=virtio ===
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing: -drive driver=file,file=TEST_DIR/t.IMGFMT,if=virtio
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > Error: Device 'virtio0' is writable but does not support snapshots
> > (qemu) info snapshots
> > No available block device supports snapshots
> > (qemu) loadvm snap0
> > Error: Device 'virtio0' is writable but does not support snapshots
> > (qemu) quit
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing: -drive driver=IMGFMT,file=TEST_DIR/t.IMGFMT,if=virtio
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > (qemu) info snapshots
> > List of snapshots present on all disks:
> > ID        TAG                     VM SIZE                DATE       VM CLOCK
> > --        snap0                      SIZE yyyy-mm-dd hh:mm:ss   00:00:00.000
> > (qemu) loadvm snap0
> > (qemu) quit
> > 
> > 
> > === Simple -blockdev ===
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=file
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > Error: Device '' is writable but does not support snapshots
> > (qemu) info snapshots
> > No available block device supports snapshots
> > (qemu) loadvm snap0
> > Error: Device '' is writable but does not support snapshots
> > (qemu) quit
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=file -blockdev driver=IMGFMT,file=file,node-name=fmt
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > (qemu) info snapshots
> > List of snapshots present on all disks:
> > ID        TAG                     VM SIZE                DATE       VM CLOCK
> > --        snap0                      SIZE yyyy-mm-dd hh:mm:ss   00:00:00.000
> > (qemu) loadvm snap0
> > (qemu) quit
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=file -blockdev driver=raw,file=file,node-name=raw -blockdev driver=IMGFMT,file=raw,node-name=fmt
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > (qemu) info snapshots
> > List of snapshots present on all disks:
> > ID        TAG                     VM SIZE                DATE       VM CLOCK
> > --        snap0                      SIZE yyyy-mm-dd hh:mm:ss   00:00:00.000
> > (qemu) loadvm snap0
> > (qemu) quit
> > 
> > 
> > === -blockdev with a filter on top ===
> > 
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
> > Testing: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=file -blockdev driver=IMGFMT,file=file,node-name=fmt -blockdev driver=copy-on-read,file=fmt,node-name=filter
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > (qemu) info snapshots
> > List of snapshots present on all disks:
> > ID        TAG                     VM SIZE                DATE       VM CLOCK
> > --        snap0                      SIZE yyyy-mm-dd hh:mm:ss   00:00:00.000
> > (qemu) loadvm snap0
> > (qemu) quit
> > 
> > 
> > === -blockdev with a backing file ===
> > 
> > Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=134217728
> > Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 backing_file=TEST_DIR/t.IMGFMT.base
> > Testing: -blockdev driver=file,filename=TEST_DIR/t.IMGFMT.base,node-name=backing-file -blockdev driver=file,filename=TEST_DIR/t.IMGFMT,node-name=file -blockdev driver=IMGFMT,file=file,backing=backing-file,node-name=fmt
> > QEMU X.Y.Z monitor - type 'help' for more information
> > (qemu) savevm snap0
> > (qemu) info snapshots
> > List of snapshots present on all disks:
> > ID        TAG                     VM SIZE                DATE       VM CLOCK
> > --        snap0                      SIZE yyyy-mm-dd hh:mm:ss   00:00:00.000
> > (qemu) loadvm snap0
> > Unexpected storage key flag data: 0
> > error while loading state for instance 0x0 of device 's390-skeys'
> > Error: Error -22 while loading VM state
> > 
> > 
> > 
> >   
> >>  
> >>>>
> >>>> 	#if defined CONFIG_TCG || !defined NEED_CPU_H
> >>>> 	extern bool icount_enabled(void);
> >>>> 	#else
> >>>> 	#define icount_enabled() 0
> >>>> 	#endif
> >>>>
> >>>> (This way, more TCG-only code in cpus.c gets elided).  You can integrate
> >>>> this change in the next version.
> >>>>
> >>>> Paolo
> >>>>  
> >>>
> >>> Weird, I tested with --disable-tcg explicitly (but may be some time ago now, as I constantly rebased).
> >>>
> >>> Will take a look at the introduction of this #defines in place of variables,
> >>> as this mechanisms will not work in the future for target-specific modules.  
> >>
> >> This is only done for per-target files so it should not be a problem.
> >>
> >> Paolo
> >>
> >>  
> > 
> >   
>