Re: [Qemu-devel] [PATCH v6 2/2] s390: do not call memory_region_allocate_system_memory() multiple times

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 17 Sep 2019 16:44:42 +0800
Peter Xu <peterx@redhat.com> wrote:

> On Mon, Sep 16, 2019 at 09:23:47AM -0400, Igor Mammedov wrote:
> > PS:
> > I don't have access to a suitable system to test it.  
> 
> Hmm I feel like it would be good to have series like this to be at
> least smoke tested somehow...
> 
> How about manually setup a very small max memslot size and test it on
> x86?  IMHO we'd test with both KVMState.manual_dirty_log_protect to be
> on & off to make sure to cover the log_clear() code path.  And of
> course to trigger those paths we probably need migrations, but I
> believe local migrations would be enough.

I did smoke test it (Fedora boot loop) [*] on s390 host with hacked
1G max section. I guess I could hack x86 and do the same for x86 guest.
Anyways, suggestions how to test it better are welcome.

*) I don't have much faith in tests we have though as it didn't
   explode with broken v5 in my case. Hence CCing ones who is more
   familiar with migration parts.

   I used 2 memslot split config at 1Gb with offline migration like this:

   $ qemu-system-s390x -M s390-ccw-virtio -m 2048 -cpu max -smp 2 -M accel=kvm  \
        --nographic --hda fedora.qcow2 -serial unix:/tmp/s,server,nowait \
        -monitor stdio 
     (monitor) stop
     (monitor) migrate "exec: cat > savefile
     (monitor) q
   $ qemu-system-s390x -M s390-ccw-virtio -m 2048 -cpu max -smp 2 -M accel=kvm  \
        --nographic --hda fedora.qcow2 -serial unix:/tmp/s,server,nowait \
        -incoming "exec: cat savefile"

> 
> And since at it, I'm thinking whether we should start assert() in some
> way in memory_region_allocate_system_memory() to make sure it's not
> called twice from now on on any board.

there is another broken board that misuses it as well,
I intend to clean that up and drop memory_region_allocate_system_memory()
altogether once s390 case is dealt with.

---
*) I don't have much faith in existing tests though as it didn't
   explode with broken v5 in my case. Hence CCing ones who is more
   familiar with migration parts.

   I've used 2 memslot split config at 1Gb with offline migration like this:

   $ qemu-system-s390x -M s390-ccw-virtio -m 2048 -cpu max -smp 2 -M accel=kvm  \
        --nographic --hda fedora.qcow2 -serial unix:/tmp/s,server,nowait \
        -monitor stdio 
     (monitor) stop
     (monitor) migrate "exec: cat > savefile
     (monitor) q
   $ qemu-system-s390x -M s390-ccw-virtio -m 2048 -cpu max -smp 2 -M accel=kvm  \
        --nographic --hda fedora.qcow2 -serial unix:/tmp/s,server,nowait \
        -incoming "exec: cat savefile"
     (monitor) cont